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The relationship of environmental factors to the structure and distribution of subtidal seaweed vegetation of the western Basque coast (N Spain)
Abstract
Subtidal vegetation distribution patterns in relation to environmental conditions (pollution, wave exposure, sedimentation, substratum slope and depth) were studied along the western Basque coast, northern Spain, by applying canonical correspondence analysis and log–linear regressions. A total of 90 species of macrophytes were recorded by systematic sampling along 21 transects. Mesophyllum lichenoides and Cystoseira baccata were the most abundant (accounting for 47% of the overall algal cover). Gelidium sesquipedale, Pterosiphonia complanata, Zanardinia prototypus, Codium decorticatum and Asparagopsis armata (Falkenbergia phase) were other macrophytes with significant cover. Ordination analysis indicates that the five environmental variables explored account between them for 52% of the species data variance. Pollution, sedimentation and wave exposure were the principal factors explaining differences in flora composition and abundance (24, 14 and 12% of the explained variance, respectively). Log–linear regressions and canonical correspondence analyses reveal that C. baccata and G. sesquipedale exhibit a negative relationship with pollution, while sediment loading negatively affects G. sesquipedale, and C. baccata cannot stand high wave exposure levels. In contrast, P. complanata and C. decorticatum show a positive relationship with pollution and can bear high levels of sedimentation and wave exposure. M. lichenoides and Z. prototypus present a wide tolerance range for all these factors. Macroalgal cover, species richness and diversity remain practically constant from unpolluted to slightly polluted sites, but they decrease sharply under moderately polluted conditions. In the same way, algal cover decreases as sediment loading increases, but diversity and species richness show the highest values at intermediate levels of sedimentation. In relation to wave exposure, maximum algal cover was achieved at very exposed habitats whereas diversity and species richness were higher under semi-exposed conditions.
... These erect fronds can have an autonomous life when fragmented and can reattach to the substrate, so vegetative propagation, through fragmentation, is a frequent method of colonisation [76]. The species has a wide distribution, occurring in Atlantic Europe [6,73,[77][78][79][80][81][82], Mediterranean Sea [83], Atlantic islands [84][85][86], Atlantic Africa [87][88][89][90], and Atlantic America [91]. Guiry also mentions populations in the Indic and Pacific oceans, namely in India, Indonesia, Korea, Vietnam, and Australia, but no published information on these locations could be found [72] (Figure 2). ...
... In response to these disruptions, shifts in the distribution patterns of canopy species occur. Notably, these shifts are observed with a decline in canopy-forming species, the increase in morphologically simpler warm-water species and coralline algae, and the progressive introduction and expansion of non-indigenous species [45,78,79,[98][99][100][101][102][103][104][105]. ...
... In response to these disruptions, shifts in the distribution patterns of canopy species occur. Notably, these shifts are observed with a decline in canopy-forming species, the increase in morphologically simpler warmwater species and coralline algae, and the progressive introduction and expansion of non-indigenous species [45,78,79,[98][99][100][101][102][103][104][105]. ...
Gelidium corneum (Giant Gelidium or Atlantic agar) is a well-known red seaweed harvested for its high-quality agar content. Agar is a mixture of the polysaccharides used in the food industry as a gelling, thickener, clarifying, and stabilizer agent. The best agar quality is also used in the laboratory as bacteriological agar. Yet, in recent years, the species has been studied for many other applications. Examples of uses are pharmaceuticals, cosmetics, food supplements, bioremediation, biofuels, biofertilizers and biostimulants, biomaterials, and nanocrystals, among others. The use of this biomass, though, raises concerns about the sustainability of the resource, since this is not a cultivated species, being harvested in the wild. Thus, other uses of G. corneum biomass increase pressure on wild stocks already stressed due to climate change. However, in a biorefinery approach, a new trend is emerging, using waste biomass rather than harvested biomass to produce new bio-based materials. These are smart solutions that transform waste into innovative products, useful for various sectors of society while reducing the impact of biomass exploitation. The aim of this review paper, thus, is to address the current state of G. corneum biology, ecology, threats, its current uses and market, and the ongoing research on innovative proposals in a circular economy framework.
... This paper seeks to assess changes over time (three sampling surveys: 1982, 2007 and 2014) in the structure of subtidal macroalgal assemblages in terms of composition and taxon biomass in the westernmost part of the Basque coast. These assemblages can be considered representative of the south-eastern Bay of Biscay since they are distributed along large stretches of coastline in this region (Gorostiaga et al. 1998;Díez et al. 2003). ...
... The study area lies at the eastern end of the Cantabrian Sea (Northern Spain), on the south-eastern Bay of Biscay. It is over 192 km in length and is open to strong waves coming mostly from the NW, with an average height of 1.9 m (Díez et al. 2003;González et al. 2004;Galparsoro et al. 2010). The south-eastern Bay of Biscay is exposed to highly exposed to the prevailing NW swells, with high, mostly erosional, energy. ...
... At the end of the study period, scattered individuals and small patches of the large macroalga G. baccata were detected. However, the ability of this fucoid to colonise shallow rocky reefs in coastal stretches exposed to strong waves is rather limited (Díez et al. 2003). Accordingly, the increase in wave energy detected since the early 1990s on the Basque coast (Borja et al. 2013) is suggested as the main factor of change explaining the decline of G. baccata in some pristine locations along this coast (Muguerza et al. 2017). ...
This study seeks to assess changes over time in the structure of subtidal macroalgal assemblages across depth in the south-eastern Bay of Biscay. The results reveal a large-scale decline in total macroalgal biomass between 1982 and 2014. However, the temporal pattern of shift differs from one depth to another: total biomass decreased at depths from 3 to 10 m, but increased at depths of 2 and 11 m. The strong decrease in biomass detected in the 3–10-m depth range is a consequence of a sharp net decline in large macroalgae biomass which was not offset by increased biomass of small species, mainly corresponding to turf-forming algae. The dominant canopy-forming Gelidium corneum in 1982 had practically disappeared by the end of the study period and its biomass loss was far from being offset by the small increase detected in the fucoid Gongolaria baccata . By contrast, at depths of 2 and 11 m, the most notable result is an increase in large species, mainly Halopithys incurva and Codium decorticatum at 2 m and G. baccata at 11 m; however, at both depth levels, a new canopy was far from being developed. These findings evidence that biomass and habitat provision, two pivotal roles of canopy-forming species in ecosystem functioning, have been altered. Further research into potential changes in primary productivity and biodiversity linked to the shift detected in assemblage structure needs to be conducted in order to get information for conservation and management decisions associated with the loss of habitat-forming macroalgae.
... The coverage of visually distinguishable sessile taxa was calculated using the Braun-Blanquet scale (1979) (Díez et al., 2003;. 6 cover-categories were used: <5% cover (1), 5-25% (2), 25-50% (3), 50-75% (4), and >75% (5). ...
... iii) Grazers' coverage, using the Braun-Blanquet (1979) scale in line with , integrating all grazers' taxa. iv) Sediment coverage followed the criteria suggested by Díez et al. (2003), keeping the same Braun-Blanquet categories used for phytobenthos coverage: (1) <5% coverage, (2) 5-25%, (3) 25-50%, (4) 50-75%, and (5) >75%. v) Topographic complexity followed the methods of Graziano et al. (2009) employed by Balistreri et al. (2015), but using the same 625 cm2 sampling squares for the calculation. ...
... The coverage values of each phytobenthic taxon, sediment and grazers were determined by using a transformation of the Braun-Blanquet scale data, considering the median points of each interval as new values (Díez et al., 2003;Guinda et al., 2012). The coverage values of the taxa were square root transformed for the multivariate analyses, and a similarity matrix was generated based on them using the Bray-Curtis distance. ...
... The coverage of visually distinguishable sessile taxa was calculated using the Braun-Blanquet scale (1979) (Díez et al., 2003;Chappuis et al., 2014). 6 cover-categories were used: <5% cover (1), 5-25% (2), 25-50% (3), 50-75% (4), and >75% (5). ...
... iii) Grazers' coverage, using the Braun-Blanquet (1979) scale in line with Chappuis et al. (2014), integrating all grazers' taxa. iv) Sediment coverage followed the criteria suggested by Díez et al. (2003), keeping the same Braun-Blanquet categories used for phytobenthos coverage: (1) <5% coverage, (2) 5-25%, (3) 25-50%, (4) 50-75%, and (5) >75%. v) Topographic complexity followed the methods of Graziano et al. (2009) employed by Balistreri et al. (2015), but using the same 625 cm2 sampling squares for the calculation. ...
... The coverage values of each phytobenthic taxon, sediment and grazers were determined by using a transformation of the Braun-Blanquet scale data, considering the median points of each interval as new values (Díez et al., 2003;Guinda et al., 2012). The coverage values of the taxa were square root transformed for the multivariate analyses, and a similarity matrix was generated based on them using the Bray-Curtis distance. ...
Abrasion platforms with vermetids shape unique seascapes and biotic assemblages that characterize several of the warm Mediterranean
coasts. The composition, structural and seasonal dynamics of the platforms’ phytobenthos were examined at two Southeast
Iberian locations through non-destructive sampling. The patterns observed were linked with environmental variables and grazers’
coverage, and we assessed their possible influence. Structural descriptors α-diversity and β-diversity were applied, pointing that
depth and season-related variables were the major influencing drivers. Higher α-diversity and β-diversity values during winter and
spring coincided with the production optimum of the community. A greater average water depth influences the abundance of both
midlittoral and infralittoral taxa. The strong resemblance between the phytobenthos of these vermetid platforms and that on similar
platforms in the Eastern and Central Mediterranean Sea suggests that these are affected by the same structuring mechanisms
... This paper seeks to investigate whether this is a general trend affecting the whole area. We therefore set out to estimate changes in the taxonomic and functional structure of subtidal macrophyte assemblages off the southeastern Bay of Biscay over the last thirty years by revisiting in 2008-2009 and 2013 a total of 19 locations that were first studied in 1991 (Díez et al., 2003;Gorostiaga et al., 1998). ...
... The sampling methodology is adapted from previous research conducted in summer 1991 (Díez et al., 2003;Gorostiaga et al., 1998). 19 of the locations studied in 1991 were revisited in 2008-2009 and in 2013 (Fig. 1). ...
... Cystoseira baccata is a lusitanic species that forms the canopy of subtidal vegetation in shallow subtidal assemblages on semiexposed shores on the central and eastern areas of the North coast of Spain (Díez et al., 2003;Fernández and Niell, 1982;Guinda et al., 2012). This large macrophyte is a warm-temperate species that shows a high capability for acclimation to increased temperature and irradiance (Miguel-Vijandi et al., 2010), and is therefore expected to expand northwards under ongoing climate change (Hiscock et al., 2004). ...
This study assesses changes in the taxonomic and functional structure and in the diversity of the shallow (3–9 m) subtidal vegetation off the southeastern coast of the Bay of Biscay by studying 19 locations between 1991 and 2013. Results provide evidence that the three-dimensional assemblages of shallow subtidal bottoms in the study area may be shifting towards less structurally complex communities. Canopy-forming algae are declining whereas simple thallus turfs composed of a combination of filamentous, polysiphonated and foliose non-corticated algae are becoming abundant along with articulated corallines and crustose species. Moreover, a significant increase in taxa richness and diversity was found, mainly due to the development of opportunistic and morphologically simple forms with warm-water affinity. The potential ecological consequences of canopy loss for coastal ecosystems are discussed. Given that changes in climate conditions are predicted to intensify, the prevalence of the new turfing space occupiers in the study area here considered seems to be realistic on the basis of their ability to compete for space and resist disturbance. Consequently, major implications for the functioning and diversity of the ecosystem and for ecosystem services may be expected.
... A total of sixteen 100 m long transects were studied along the coastline including the current availability of canopy forming algae resources in non-contaminated areas (Fig.1). The sampling transects were placed on the basis of reference information from previous studies in the area (Díez et al., 2003;Gorostiaga et al., 1998) selecting only stretches of coast under good environmental conditions (Borja et al., 2016;Borja et al., 2009). This was necessary to distinguish the effect of canopy abundance on benthic ecological properties from variations that might be caused by local differences due to anthropogenic disturbances. ...
... Invertebrate species not identified in the field were preserved in formalin or alcohol. Within the study area, large macrophyte stands were mostly structured with the perennial canopy of Gelidium corneum and Cystoseira baccata (Díez et al., 2003;Gorostiaga et al., 1998). Both communities utilize the space trough a complex vertical layering which consists of a well-developed crustose layer, an underlying layer dominated by small red algae, a well-developed canopy of G. corneum or C. baccata, and a summer epiphytic layer on the canopy . ...
... Replicates (n) within each level of factor Ca were unequal due to the natural abundance of algae in the rocky subtidals in the years studied. Previous research from the study area (Díez et al., 2003) found that within the bathymetrical range considered in the present study, the macroalgal community structure exhibited low variation in relation with depth. Therefore, we assume that the potential confounding effect of depth with the factor Canopy Cover is low. ...
Canopy-forming seaweeds provide specific habitats with key ecological properties and are facing severe declines worldwide with unforeseeable consequences for ecosystem processes. Investigating the loss of such natural habitats in order to develop management strategies for conservation is a major challenge in marine ecological research. This study investigated the shallow rocky bottoms of the southern Bay of Biscay at two sampling times with a view to identifying the effect of canopy seaweed availability on the taxonomic and functional properties of invertebrate multivariate structure, abundance, density, diversity and evenness. The multivariate taxonomic and functional structure of assemblages changed significantly according to canopy availability in terms of taxa and functional groups abundance, but no substantial change was observed in composition. Biogenic habitat simplification resulted in a decrease in total invertebrate abundance and in taxonomic and functional density and diversity, whilst no effects were observed in taxonomic and functional evenness. Loss of canopy involved an impoverishment of the whole community particularly for epiphytic colonial sessile suspension-feeders, but it also extended to non-epiphytic forms. Our results emphasize the importance of canopy decline as a major driver of changes in benthic ecosystem properties and highlight that biogenic space provided by canopy is a limiting resource for the development of rocky subtidal invertebrates.
... In addition, a moderate wave action might wash away any sediment and prevent sediment deposition that could inhibit the recruitment of algae to the plots. Also, algae can benefit from the moderate waves or water movement that can enhance photosynthesis, nutrient uptake and light, remove epiphytes and waste products (Díez et al. 2003;Stewart & Carpenter 2003;Kregting et al. 2016). However, the study of Inoue et al. (2020) showed that the canopy of Sargassum siliquastrum collapsed and deformed when water velocity increased that enhanced self-shading and led to the decline in gross photosynthesis rates. ...
... Many studies indicated that sediments can smother surfaces precluding successful attachment and settlement of algae and bury existing recruits causing anoxia and mortality (Geange et al. 2014;Gao et al. 2019;Schiel & Gunn 2019). Hence, wave action plays an important role in controlling algal recruitment and abundance (Díez et al. 2003). ...
Zonation patterns and the structure of intertidal communities are controlled by tidal conditions. Algal diversity, abundance and succession were experimentally tested under different degrees of wave exposure, shore level, and season of clearing at the intertidal zone, Phuket, Thailand. Dead coral patches colonized by algae (20 cm × 20 cm) were cleared at upper, middle, and lower shore levels on sheltered and semi‐exposed shores during both the dry and rainy seasons. Of 17 algal species, including eight Rhodophyta, eight Chlorophyta, and one Phaeophyceae that were recruited on the cleared plots, three species were dominant: Ulva paradoxa, Padina in the Vaughaniella stage, and Polysiphonia sphaerocarpa. Algal diversity on the semi‐exposed shore was higher than on the sheltered shore. In the successional process, U. paradoxa extensively recruited and persisted longer on plots cleared at the middle shore level on the semi‐exposed shores than at the other. It showed a greater abundance in the plots cleared in the rainy season than those cleared in the dry season. Ulva paradoxa persisted for around 5 to 6 months after clearing and was then replaced by the two later species, Padina in the Vaughaniella stage and P. sphaerocarpa. Ulva paradoxa settled more easily and persisted longer at the cleared plots than other algal species because of its opportunistic characteristics and a special physiological adaptation to long periods of emersion. From this study, degree of wave exposure, shore level, and season of clearing likely play important roles in algal recruitment, abundance, and succession patterns.
... Thus, bottom topography and sand deposits determine the distribution of this species. In exposed coastal stretches (N or NE facing) and generally in the shadow of coastal headlands and ledges, C. baccata is dominant both on sand-free substrates and sandy rocky substrates (Diez et al., 2003). Although the stretch of coast studied in this research is NW facing, the shadow effect of Cape Higuer and the dominance of rocky bottoms would explain the predominance of extensive C. baccata stands. ...
... The first species is present from the infralittoral zone to 3 m depth and rarely deeper (Gorostiaga et al., 2004;de Casamajor et al., 2018), whereas C. baccata shows a significant wider bathymetric range, from the infralittoral fringe to 25 m depth (Gorostiaga et al., 2004;Castro et al., 2006). These large algae harbour a crustose and basal layer mainly composed of red algae (Diez et al., 2003;Pinedo et al., 2007). ...
... The effects of coastal eutrophication on rocky shore assemblages manifest as a widespread shift from assemblages characterized by slow-growing macroalgae to a dominance of fast-growing ephemeral macroalgae (Díaz, 2002;Díez et al., 2003;Worm & Lotze, 2006;Arevalo et al., 2007;Pinedo et al., 2013), with a consequent loss of ecological quality of the system (Arevalo et al., 2007;Pinedo et al., 2013). In this context, any information about mechanisms driving these shifts may be useful to predict consequences of anthropogenic pressures and manage coastal ecosystems. ...
... Long exposure to high concentrations of nutrients did not affect the abundance of C. brachycarpa, the percentage cover of which regressed throughout the study period. A decline in large brown and perennial macroalgae under eutrophic conditions is a widely observed phenomenon (Díez et al., 2003;Liu et al., 2007;Connell et al., 2008) which is probably linked more to indirect than to direct effects of nutrient enrichment. Negative effects of urban waste-waters on the photosynthetic efficiency of brown algae have been observed (Scherner et al., 2012); exposure to sewage effluent also seriously damages the recruitment of these species (declines in zygote germination, delays in embryo growth and increases in mortality) (Doblin & Clayton, 1995) and facilitates the replacement of large brown or perennial algae by opportunistic species, by virtue of differences in their nutrient uptake rates (Middelboe & Sand-Jensen, 2000;Connell et al., 2008). ...
Increase of nutrient concentrations in coastal waters is a worldwide phenomenon with ecological consequences for natural assemblages. Little is known about species-specific nutrient dynamics among macroalgae in the Mediterranean Sea, which may be key to understanding competitive strategies driving the structure of macroalgal assemblages. We conducted an in situ nutrient enrichment experiment to evaluate whether increasing nutrient availability modified the relative abundance of the three dominant brown macroalgae Cystoseira brachycarpa, Halopteris scoparia and Padina pavonica and whether any such modifications were related to different nutrient dynamics of the three macroalgae under different chronic enrichment regimes. Tissue nitrogen, carbon and phosphorus were determined 6 and 18 months after the first exposure to nutrient enrichment. Under nutrient-enriched conditions, C. brachycarpa decreased in abundance over the experimental period, while P. pavonica and H. scoparia increased (albeit with different trends), the former mostly in the earlier phase and the latter in the subsequent phase. Nutrient content of the three macroalgae responded positively to enrichment in the first year, although it was exploited differently: C. brachycarpa only increased its internal reserves, while H. scoparia and P. pavonica also used available nutrients for growth. A completely different pattern was observed in the second year, as nutrient content of all macroalgae was affected very little, if at all, by nutrient enrichment. However, the different responses in terms of abundance observed during the second year indicated changing nutrient dynamics across species over the longer timescale of nutrient exposure. The results of the study confirmed the existence of species-specific response patterns of nutrient dynamics in the three macroalgae. They also suggest that nutrient dynamics are habitat-specific, since nutrient response was strongly conditioned by macroalgal tissue nutrient status, which reflects the nutrient history of the site.
... Thus, bottom topography and sand deposits determine the distribution of this species. In exposed coastal stretches (N or NE facing) and generally in the shadow of coastal headlands and ledges, C. baccata is dominant both on sand-free substrates and sandy rocky substrates (Diez et al., 2003). Although the stretch of coast studied in this research is NW facing, the shadow effect of Cape Higuer and the dominance of rocky bottoms would explain the predominance of extensive C. baccata stands. ...
... The first species is present from the infralittoral zone to 3 m depth and rarely deeper (Gorostiaga et al., 2004;de Casamajor et al., 2018), whereas C. baccata shows a significant wider bathymetric range, from the infralittoral fringe to 25 m depth (Gorostiaga et al., 2004;Castro et al., 2006). These large algae harbour a crustose and basal layer mainly composed of red algae (Diez et al., 2003;Pinedo et al., 2007). ...
Cystoseira baccata, a biological quality element for the implementation of the Water Framework and Marine Strategy EU Directives, is a dominant species in the subtidal rocky bottoms of the Basque coast. As part of this issue and given the need to better understand the functional character of benthic rocky ecosystems and use them as a reference to anthropogenic changes, two samplings campaigns were conducted in 2014 and 2017. Several population parameters (i.e. frond density, frond length frond-length/total frond-length ratio and taxonomic richness of epibionts) of C. baccata were studied from three sites monitored within the Water Directive Framework in relation to bathymetry during the two campaigns. The results showed a significant influence of bathymetry on frond density, frond length and the epibiotic load, and also an effect of sampling time for the seaweed and epibionts (epiflora and epifauna). The characterization of these functional population parameters for C. baccata under natural conditions are extremely valuable for its application to monitoring programs evaluating the ecological status of coastal waters in this region.
... Cladophora spp. among the macroalgaes and Spionidae species like Boccardia proboscidea among the polychaetes) (Soltan et al., 2001;Díaz et al., 2002;Díez et al., 2003;O'Shanahan Roca et al., 2003;Borja et al., 2006;Arévalo et al., 2007;Wells et al., 2007;Jaubet et al., 2011;Kotta and Moller, 2014;Cabrita et al., 2015). ...
... decreased richness in sites 2 and 4). In many studies around the world, differences in diversity, total abundance and species composition between impacted and non-impacted areas was observed where species richness and diversity decreased under polluted conditions (Gorostiaga and Díez, 1996;Díez et al., 2003;Arévalo et al., 2007;Wells et al., 2007;Elías et al., 2014). In general those patterns are consistent with the typical dominance of ephermeral green algae association in enriched condition (e.g. ...
The sewage pollution impact over coastal environment represents one of the main reasons explaining the deterioration of marine coastal ecosystems around the globe. This paper aims to detect promptly a putative sewage pollution impact in a Southwestern Atlantic coastal area of Argentina as well as to identify a straightforward way for monitoring, based on the relative abundance coverage of the intertidal epilithic taxa. Four sampling sites were distributed at increased distances from the sewage outfall where the cover of individual epilithic species was visually estimated. The surrounded outfall area (i.e. outfall site) resulted polluted with high percentages of organic matter in sediment and Enterococcus concentration in seawater. The structure of the community showed a remarkable difference between the polluted site (outfall site) and the unpolluted sites. The polychaete Boccardia proboscidea dominated the outfall site with variable abundances of the green algae Ulva sp. during the period of study, decreasing the diversity of the community, while the mussel Brachidontes rodriguezii and variable abundances of several algae species dominated the unpolluted sites. The monitoring of the benthic community represents an effective, non-destructive, relative inexpensive and rapid method to assess the health of the coastal environment in the study area. The large abundance of B. proboscidea along with the absence of B. rodriguezii individuals at <300m to the sewage outfall discharge allowed the success of this classical monitoring method in a temperate marine-coastal ecosystem with certain gradient of pollution.
... Few studies have addressed how physical and biological factors factors Fig. 4 Cluster analysis of zonation pattern for macroalgae biomass data using Bray-Curtis similarity index influence seaweed community dynamics in the Persian Gulf. However, the result of studies from other parts of the world revealed that abiotic factors such as substratum, nutrients, water motion, sedimentation, pollution and herbivores affect the structure and distribution of algal communities at a local scale (Dıez et al. 2003). ...
... Palisada perforata which was scarce in site 1 is characteristic of oligotrophic waters (Moreira et al. 2006). Centroceras clavulatum (Ceramiaceae), on the other hand, is an annual alga resistant to the pollution (Dıez et al. 2003). Moreover, Caulerpa spp. ...
This study investigates the spatial and temporal variation of intertidal macroalgae along the eastern coasts of Qeshm Island, Persian Gulf, Iran. Monthly sampling of abundance, biomass, richness and diversity of macroalgae at three intertidal levels was carried out at two different sites during 1 year. The samples were collected every month using quadrats (0.5 × 0.5 m) from October 2012 to September 2013. The species dry weight was applied to examine changes in biomass and assemblage composition of intertidal macroalgae using univariate and multivariate analyses. A total of 42 seaweed species (10 Chlorophyta, 9 Phaeophyceae, and 23 Rhodophyta) were identified. The results confirmed a temporal pattern in the growth of the algal species which also showed a biomass zonation pattern from upper to lower intertidal. The annual mean biomass of macroalgae was highest in winter (29.3 ± 9.8 g dry wt m−2) and the lowest in autumn (17.3 ± 13.5 g dry wt m−2). The annual dominant species by biomass was Padina sp. followed by Padina australis. The most common species in the area, during the sampling period include Ulva intestinalis, Ulva lactuca, Palisada perforata and Padina sp. According to the similarity percentages analysis (SIMPER), the species Ulva intestinalis, Dictyosphaeria cavernosa (Chlorophyta), Padina australis (Phaeophyceae), Champia spp., Centroceras clavulatum and Palisada perforata (Rhodophyta) were responsible for the most dissimilarity of species composition between four seasons during the sampling period. BIOENV analysis indicated that the main environmental factors structuring macroalgal community at the study area were TDS and pH. The simple macroalgae community on the eastern coast of Qeshm Island and absence of slow-growing perennial macroalgae, such as members of the Sargassaceae, known from the lower shore at other intertidal localities along the island’s coast might relate to the predominantly unsuitable sandy-stony substrates unsuitable for their colonization and the unfavourable impact upon them of urbanization.
... Influence of depth, sedimentation, rugosity, slope and substratum diversity. To assess spatial variation at a scale of meters, depth and main habitat-complexity variables which recur in the bibliography were identified: (1) sedimentation (Alves et al. 2001, Díez et al. 2003, Erikson and Bergström 2005, (2) topographic complexity or rugosity of the substrate (Luckhurst and Luckhurst 1978, Robert and Ormond 1987, Jennings et al. 1996 McClanahan 1994), (3) slope (Alves et al. 2001, Díez et al. 2003, (4) substratum diversity (Gratwicke and Speight 2005). The effect of each variable on D. aff. ...
... Influence of depth, sedimentation, rugosity, slope and substratum diversity. To assess spatial variation at a scale of meters, depth and main habitat-complexity variables which recur in the bibliography were identified: (1) sedimentation (Alves et al. 2001, Díez et al. 2003, Erikson and Bergström 2005, (2) topographic complexity or rugosity of the substrate (Luckhurst and Luckhurst 1978, Robert and Ormond 1987, Jennings et al. 1996 McClanahan 1994), (3) slope (Alves et al. 2001, Díez et al. 2003, (4) substratum diversity (Gratwicke and Speight 2005). The effect of each variable on D. aff. ...
Diadema aff. antillarum performs a key role in organizing and structuring rocky macroalgae assemblages in the Canary Islands; increased sea urchin population density can result in the formation of rocky grounds covered with crustose algae. In the Canary Islands this type of system alternates with non-crustose macroaleal systems. However, understanding of the process controlling formation, persistence and alternation between states is still poor. Moreover, knowledge of spatial and temporal variations of this key herbivore populations are scarce. Here an extensive study of D. aff. antillarum populations throughout the Canarian Archipelago were presented, with particular emphasis on two main themes: firstly the influence Of Sea urchin population on non-crustose macroalgal assemblages. Secondly, the spatial variation of adult sea urchin populations at different scales: both on a large scale (between islands and sites with different wave exposure) and on a medium-small scale (between depths and habitats with different characteristics), and including comments regarding human influence on the observed spatial pattern between the studied islands. The main results were: (1) densities of D. aff. antillarum higher than 4 ind.m(-2) drastically reduce non-crustose macroalgal cover to under 30%; (2) Tenerife Island comprises the highest urchin densities while El Hierro has been found to have the lowest; (3) wave exposure is a factor determining sea urchin density: more highly exposed sites present lower urchin density and vice versa; (4) rocky grounds covered with crustose algae can be found at greater depth in more highly exposed sites and at shallower depths in lesser exposed sites; (5) when sand percentage over the rocky substrate exceeds 20%, urchin density is limited to under 1 ind.m(-2) and (6) high relief rocky Substrate present higher urchin densities and hence a lower non-crustose macroalgal cover. Rev. Biol. Trop. 56 (Suppl. 3): 229-254. Epub 2009 January 05.
... The water's residence time may also impact the seaweed composition, which determines the likelihood that nutrients will be converted into new biomass [41]. This study demonstrated spatial synchronicity in seaweed fractions where seasonal differentiation was typically possible, independent of the sampling site. ...
The main goal of this study was to assess the bioactive and polysaccharide compositions, along with the antioxidant and antibacterial potentials, of five seaweeds collected from the northeastern coast of Algeria. Through Fourier transform infrared spectroscopy analysis and X-ray fluo-rescence spectroscopy, the study investigated the elemental composition of these seaweeds and their chemical structure. In addition, this study compared and identified the biochemical makeup of the collected seaweed by using cutting-edge methods like tandem mass spectrometry and ultra-high-performance liquid chromatography, and it searched for new sources of nutritionally valuable compounds. According to the study's findings, Sargassum muticum contains the highest levels of extractable bioactive compounds, showing a phenolic compound content of 235.67 ± 1.13 µg GAE·mg⁻ 1 and a total sugar content of 46.43 ± 0.12% DW. Both S. muticum and Dictyota dichotoma have high concentrations of good polyphenols, such as vanillin and chrysin. Another characteristic that sets brown algae apart is their composition. It showed that Cladophora laetevirens has an extracted bioactive compound content of 12.07% and a high capacity to scavenge ABTS + radicals with a value of 78.65 ± 0.96 µg·mL −1 , indicating high antioxidant activity. In terms of antibacterial activity, S. muticum seaweed showed excellent growth inhibition. In conclusion, all five species of seaweed under investigation exhibited unique strengths, highlighting the variety of advantageous characteristics of these seaweeds, especially S. muticum.
... Despite the limitations of our work, we believe our study holds considerable value as it can be of use as an early warning system for potential shifts in biological communities in the region. Notably, this study initiated the foundation for more expansive monitoring studies along the Basque Coast (Díez et al., 2003(Díez et al., , 2012Gorostiaga et al., 1998;Muguerza et al., 2017), and unveiled the initial stress symptoms associated with climate change in the area (Muguerza et al., 2022b). ...
Global warming is triggering significant shifts in temperate macroalgal communities worldwide, favoring small, warm-affinity species over large canopy-forming, cold-affinity species. The Cantabrian Sea, a region acutely impacted by climate change, is also witnessing this shift. This study delved into the impacts of increasing sea surface temperature on the subtidal macroalgal communities in the southeastern Bay of Biscay over the last four decades, by using data from the years 1982, 2007, 2014, and 2020. We found that temperature has shaped the community structure, with warm-affinity species steadily displacing their cold-affinity counterparts. Notably, new communities exhibited a profusion of smaller algal species, explaining the observed increased biodiversity within the area. In the last period investigated (2014–2020), we observed a partial recovery of the communities, coinciding with cooler sea surface temperatures. Shallow algal communities were more reactive to temperature variations than deeper communities, possibly associated with higher exposure to increased temperatures. Our study offered insights into the intricate relationship between the changes in ocean temperature and algal species in the southeastern Bay of Biscay, shedding light on the ongoing ecological shifts in this region.
... Comparison with data on Indian seaweed diversity Bolton (1994) stated that tropical regions have high species numbers due to high environmental stability over a long time. Abiotic factors such as substratum, nutrients, water motion, sedimentation, pollution, and herbivores affect the structure and distribution of algal communities at a local scale (Diez et al. 2003). The potential area of seaweed growth in India's southeast coast is the Gulf of Mannar coastal regions starting from Rameswaram and ending in Kanyakumari (Kaliaperumal et al.1998). ...
A two-year study was conducted to analyze and document the seaweed diversity available along the intertidal zone of islands of the Gulf of Mannar Marine Biosphere Reserve from May-18 to October-19 with four-month intervals. From the five consequent surveys, 137 seaweed species belonging to 32 families and 17 genera were recorded in the Gulf of Mannar islands. Among 137 seaweed species, green algae (48) was the highest, followed by red (48) and brown (41) were observed. A comparative study among all three seasons revealed that a higher number of seaweed species and diversity indices were recorded in post-monsoon and monsoon seasons, whereas a lower value was recorded in summer months. 30 species were commonly found in the Gulf of Mannar Biosphere Reserve islands and 44 species are found with restricted occurrence. The genus Caulerpa appeared as the most diversified genera (18 species) followed by Sargassum (14 species), Dictyota (8 species), Gracilaria (6 species), Turbinaria (4 species), and Hypnea (6 species). While comparing all 19 islands, the maximum number of species recorded in Appa and Hare island (n = 76) and minimum species recorded in Manaliputti island (n = 25). There were 10 seaweed species abundantly present in all 19 islands. Dictyota dichotoma, Halimeda gracilis, Padina pavonica, Sargassum polycystum, Turbinaria ornata were common. Both the indices clearly pointed out greater seaweeds diversity in all the islands except Manaliputti island and higher diversity value indicated the healthy nature of the seaweed ecosystems and islands of the Gulf of Mannar Marine Biosphere Reserve. Highlights
... The BRT models developed for both E. radiata and P. comosa showed that current speed, wave orbital velocity, temperature, connectivity, substrate complexity, and urchins contributed to explaining the variability in the overall decreasing population status of each species. The positive relationship between current speed and E. radiata and P. comosa percent cover shows that water motion is often beneficial to kelps as it can increase nutrient uptake (Hurd, 2000;Wheeler, 1988), increase irradiance by pushing the fronds in different directions (Leigh Jr. et al., 1987), and remove excess waste in the vicinity of the plants (Dıéz et al., 2003). However, not all water motion has a positive influence on kelp. ...
Aim
Kelp forests throughout temperate regions of the world serve as foundation species that play a critical role in sustaining the health and function of marine ecosystems but are experiencing declines in abundance due to a loss in resilience as the ocean climate changes. Ocean warming along southeast Australia has already been linked to dramatic losses of kelp species and is contributing to the range expansion and population increases of two species of sea urchin. This research attempts to understand the impact of multiple stressors on the decline in kelps in this region.
Location
Coastal Waters of Victoria, Southeast Australia.
Methods
In this study, we use long‐term (>20 years) datasets on biological observations across Victorian waters to determine trends in coverage and the impact of multiple environmental variables (oceanography, habitat, and urchin abundances) on two important kelps that serve as foundation species (Phyllospora comosa and Ecklonia radiata) using boosted regression trees. These models were then used to develop predictive distribution models for each species and also to project abundance distributions into the future.
Results
We found that both kelp species are decreasing in percent coverage over time with multiple environmental variables contributing to these declines, including increasing temperatures, intensifying wave energy, changes in currents and recruitment patterns, and increases in urchin populations. Additionally, future projections of temperature, wave energy, and urchin populations show that both species will continue to decrease across 62%–94% of their range by 2090.
Main conclusions
Long‐term biological datasets allowed us to develop maps of the past, current, and future distributions of these important foundation species, providing valuable information to managers for prioritization of areas for targeted urchin management and restoration of kelps. Understanding the environmental factors affecting their distribution helps guide manager restoration investments in regions where kelp populations are most likely to persist in the future.
... Comparison with data on Indian seaweed diversity Bolton (1994) stated that tropical regions have high species numbers due to high environmental stability over a long time. Abiotic factors such as substratum, nutrients, water motion, sedimentation, pollution, and herbivores affect the structure and distribution of algal communities at a local scale (Diez et al. 2003). The potential area of seaweed growth in India's southeast coast is the Gulf of Mannar coastal regions starting from Rameswaram and ending in Kanyakumari (Kaliaperumal et al.1998). ...
A two-year study was conducted to analyze and document the seaweed diversity available along the intertidal zone of islands of the Gulf of Mannar Marine Biosphere Reserve from May-18 to October-19 with four-month intervals. From the five consequent surveys, 137 seaweed species belonging to 32 families and 17 genera were recorded in the Gulf of Mannar islands. Among 137 seaweed species, green algae (48) was the highest, followed by red (48) and brown (41) were observed. A comparative study among all three seasons revealed that a higher number of seaweed species and diversity indices were recorded in post-monsoon and monsoon seasons, whereas a lower value was recorded in summer months. 30 species were commonly found in the Gulf of Mannar Biosphere Reserve islands and 44 species are found with restricted occurrence. The genus Caulerpa appeared as the most diversified genera (18 species) followed by Sargassum (14 species), Dictyota (8 species), Gracilaria (6 species), Turbinaria (4 species), and Hypnea (6 species). While comparing all 19 islands, the maximum number of species recorded in Appa and Hare island (n = 76) and minimum species recorded in Manaliputti island (n = 25). There were 10 seaweed species abundantly present in all 19 islands. Dictyota dichotoma, Halimeda gracilis, Padina pavonica, Sargassum polycystum, Turbinaria ornata were common. Both the indices clearly pointed out greater seaweeds diversity in all the islands except Manaliputti island and higher diversity value indicated the healthy nature of the seaweed ecosystems and islands of the Gulf of Mannar Marine Biosphere Reserve.
Highlights
First attempt to systematic document of the seaweed diversity exclusively in inter-tidal region of islands of Gulf of Mannar Marine Biosphere Reserve
Analyse the healthy nature of seaweed diversity Gulf of Mannar Marine Biosphere Reserve
Analysing seasonal impact, seaweed dominance, succession pattern in inter-tidal region of islands of Gulf of Mannar Marine Biosphere Reserve
Data generated in this study may act as baseline information for effective coastal management
... It was founded that there were some secondary covers obscuring the primary covers on some attaching substrates, and these secondary covers were classified as the taxon under that substrate. The diversity and dominance of organisms were respectively determined by the Shannon-Wiener diversity index (H ′ ) and dominance index (Y), and the Y was used to determine the dominant species of organisms (Diez et al., 2003), calculated as follows: ...
Artificial reefs (ARs) are often used to restore and develop seaweed beds. However, few studies have reported the changes of biological community on the substrate surface before and after the attaching substrates were transferred. In this study, the response of the biological community, including macrobiotic biofouling and microbial community, to translocation of seaweed attaching substrate were investigated. The results showed that the seaweed coverage ratio significantly reduced after the translocation, the macrobiotic biofouling community diversity on attaching substrates increased after the translocation, and the transplanted substrates had more percentage cover and lower biodiversity than the untransplanted substrates. In addition, highest diversity was found on microbial community after the translocation. Non-metric multidimensional scaling (NMDS) revealed that the microbial community on the transfered substrates was significantly different from that before and without transfer. Co-occurrence network analysis showed that the degree of bacterial community network connection was highest before the translocation. The result revealed that the translocation of seaweed substrate could affect the biological community composition, and could accelerate the changes in macrobiotic biofouling community on the back of substrates.
... This macroalga could be a good alternative to offset the loss of the current canopy-forming species, since it is a warmer-affinity species which can stand higher temperature and irradiance levels (Miguel-Vijandi et al., 2010). However, Díez et al. (2003) find that it cannot tolerate heavy hydrodynamics. The future wave regime will therefore determine whether or not this species becomes the future substitute of cooler-affinity biogenic species. ...
The effect of climate change on species distribution has been the focus of much recent research, but the community-level approach remains poorly studied. Our investigation applies a present assemblage-environment relationship model for the first time to the predict changes in subtidal macroalgal assemblages in the northern Iberian Peninsula under the RCP 4.5 and RCP 8.5 climate scenarios by 2100. Water temperature is the most relevant factor in shaping assemblage distribution, whilst nutrient availability plays a secondary role. The results partially support our hypothesis that there may well be a potential meridionalisation of northern Iberian assemblages in the future. Under the most pessimistic scenario, the model projects that the north-western assemblages will remain distinct from the rest, whereas the central and eastern assemblages of the north coast of the Iberian Peninsula will come to resemble those of the Mediterranean region more closely than those of the northwest coast. This research may help predict how the biodiversity of the coastal ecosystem will respond to new environmental conditions. This is essential information for developing proper management and conservation policies.
... In addition, Diez et al. (2003) reported that the sedimentation could also affect the composition and abundance of seaweeds. found that an increase in Total Suspended Solids (TSS) from construction activities resulted in decreased biomass production at a coral reef flat. ...
This thesis examines the social, economic and environment aspects of boat based recreational fishery in the marine district of Port Dickson, Negeri Sembilan, Malaysia. It identifies the primary fishing techniques used and species and volumes harvested and compared with the artisanal fishermen who also fished in the same waters. The Port Dickson District’s waters supported an important recreational fisheries industry, with 30 landing points utilised for that purpose. Anglers fished from boats rented from fishermen and commercial boat operators, kelong (privately owned fishing platforms), purpose built public jetties and breakwaters. Data was collected at these recreational fishing landing points indicated that activity was dominated by shore angling and boat angling. A wide range of species were caught include some such as the cobia (Rachycentron canadum) that did not appear in official fisheries statistics. The main bait types that were used included live prawn, squid, small fish and pumpum (polychete worms) as bait. The use of artificial bait or lures was almost non-existent. The paper describes a method for estimating the value of recreational fishery in Port Dickson based on fishing effort derived from interviews and discussions with recreational fishes. The investigation indicated that boat fishing in Port Dickson involved 10,066 anglers with a total fishing effort of 23,048 person-day with expenditures that amounted to RM1,490,062. Annualised catch volume, the total boat-based recreational fisheries catch is estimated to have amounted to 592 tonnes, which is not far from 2018 artisanal fisheries catch of 670 tonnes. In many landing points, recreational fisheries was found to be a major contributor to the local economy. The relationship of existing recreational fishing patterns in relation to the Port Dickson District’s natural capital was explored and discussed, especially in relation to the ability of the fishers to identified hitherto unknown habitats. The uptake by boat based recreational fisheries undermines the assumptions on which existing fisheries management regimes, which is based entirely on artisanal fishing catch, is also discussed. However, it is important to note that the findings of the under-represents the economic value of off this activity as the research does not investigate the value generated through a range of related economic supply chain activities. The study described the potential value of less visible activities in coastal areas, the need to develop appropriate modelling tools with which take account of this value and the significant role of novel approaches to measuring this value.
... are characterized by high growth at high nutrient concentrations and a rapid uptake rate of nutrients, resulting in algal blooms [32,53]. Several studies have reported a decline in species diversity and an increase in opportunistic species, such as Ulva spp., upon exposure to sewage discharge [54][55][56]. Blooms of Ulva spp. resulted in a decline in species richness and diversity in a macroalgal community near a sewage outfall [57]. ...
This study aimed to investigate the dynamics of the nutrient budget of a macroalgal
community exposed to water discharged from aquaculture farms. This study was conducted in the coastal area exposed to water discharged from aquaculture farms located on Jeju Island, Korea, in May and October of 2017. Water-column-dissolved inorganic nutrient concentrations were higher in the intertidal zone than in the subtidal zone. High nutrient concentrations in the intertidal zone resulted in the bloom of Ulva spp., consequently leading to a low species number. This indicates the vulnerability of the intertidal macroalgal community to discharge from land-based aquaculture. Ecklonia cava contributed to 29–53% of the total incorporation of carbon (C), nitrogen (N), and
phosphorus (P) in the subtidal zone. In the intertidal zone, the highest tissue N content was found in Ulva spp. due to the high and rapid nutrient uptake rate from the effluent with high nutrient concentrations, thereby indicating high total N incorporation. The estimated total C, N, and P incorporation rates by macroalgae were 181.5, 8.6, and 0.95 tons year1, respectively. These results suggest that the macroalgal community in this area absorbs or removes large amounts of nutrients from the water column and plays an important role in the budgets and cycling of nutrients in the surrounding coastal areas.
... Burrows et al. 2008). Finally, a similar gradual (either positive or negative) relationship has been re ported for subtidal macrophytes on the western Basque coast (Díez et al. 2003). Consequently, any deviations from this expected pattern should be interpreted as reflecting other processes, of biotic nature. ...
Physical constraints, and particularly hydrodynamics, are major drivers of macroalgal canopy-dominated rocky shore communities. The abundance of habitat-forming seaweeds decreases with increasing wave exposure, triggering cascading effects on their associated communities. This study aims at describing the structure of benthic communities along a hydrodynamic gradient and understanding the role of wave height in structuring the ecological transition from macroflora to macrofauna dominance. In situ wave height was measured together with biological communities (macroalgae, macrograzers and sessile fauna) along an exposure gradient on 3 rocky shores of western Brittany. Results showed that Fucales cover and the abundance of several understory organisms are negatively correlated to in situ wave height, except for barnacles and limpets which were positively correlated. Results revealed the occurrence of a wave height threshold at approximately 80 cm from high to mid-shore levels. Beyond this threshold, we observed a large dominance of barnacles, while below this threshold, Fucales and the associated organisms abounded. A similar threshold was observed on low shore habitats, for barnacle cover only. The results of this study challenge the commonly accepted paradigm of a gradual shift from seaweed-dominated to sessile fauna-dominated zones with increasing wave exposure on rocky shores. Finally, this study sheds new light onto interspecific interactions which drive the structure of rocky shore-associated communities.
... Turbidity, abrasion, nutrient concentrations or presence of pollutants have a great influence in the occurrence of G. baccata. In this sense, G. baccata has been demonstrated to have low tolerance to pollution (Díez et al., 2003), hence, that this specie is usually considered to be a good quality indicator in most of the methodologies proposed to evaluate the ecological status of this biological element (Juanes et al., 2008;Wells et al., 2007). The sampling site at Comillas (Cantabria, Spain) is an exposed north-facing rocky shore covered by well-developed forest of the macroalgae G. baccata in commercially exploitable quantities. ...
Gongolaria baccata (S.G. Gmelin) is marine brown seaweed mainly found on the coasts of the Baltic Sea south to the Mediterranean Sea, Canary Islands, Mauritania and Western Sahara. Herein, we report the cell viability and protective effects attributed to molecular mechanisms underlying antioxidant response to survive oxidative stress injuries. Caco-2 cells were submitted to oxidative stress by treatment with tert-butylhydroperoxide (tert-BOOH). The extract prevented cell damage and enhanced activity of antioxidant defenses (NQO1 and GST activities and GSH levels) reduced by treatment with tert-BOOH. The increases of MDA levels, the amount of intracellular ROS and caspase 3/7 activity induced by tert-BOOH were prevented when cells were treated with the G. baccata extract. Moreover, G. baccata extract caused up-regulation of GSTM2, Nrf2, and AKT1 gene expressions, as well as G. baccata extract reduced significantly Bax, BNIP3, APAF1, ERK1, JNK1, MAPK1, P38, P53, NFκB1, TNFα, IL-6, IL-1β and HO-1 gene expressions related to apoptosis, proinflammation and oxidative stress induced by tert-BOOH. These results suggest that G.baccata extract protected the cells against oxidative damage and inflammation; protective effects that could be linked to their bioactive constituents. Hence, this brown seaweed G.baccata extract could be used for the development of functional foods and/or nutraceuticals.
... For example, in most macroalgal communities on shallow rocky bottoms, variables including depth, wave exposure, sedimentation, nutrients and herbivory can explain most of the variability in the structure and diversity of the macroalgal communities (e.g. Díez et al., 2003;Sangil et al., 2011), but in in some habitats, variables associated with the rocky substrate itself can be important drivers of diversity. In unstable substrate (boulder fields, and cobble or gravel bottoms), waves, fetch and groundswell affect the movement of the rocky substrate and, therefore to the final structure of the macroalgae community (Hans Kautsky and Van der Maarel, 1990). ...
Subtidal unstable bottoms are sensitive to the environmental disturbances that determine the structure of macroalgal communities. Here, three variables (substrate size, depth and site) are tested together to explore their effect on the community structure on cobble and gravel bottoms. Diversity metrics (richness per sample, richness per area, diversity (H '), total cover), cover of life forms (hypnophyceae, ephemerophyceae, phanerophyceae, hemiphanerophyceae, chamaephyceae) and cover of the predominant species (Harveylithon samoënse, Jania pedunculata var. adhaerens, Lobophora spp., Canistrocarpus cervicornis, Halopteris scoparia) are used as descriptors of communities. Descriptors response was modeled using multiple regression analyses, in which each descriptor was considered separately as the dependent variable, while substrate size, depth and site was used as independent variables. Results show the substrate size was the most important variable with depth only being important for some perennial species although there was often site-site variability in these patterns. Richness per sample of macroalgal communities increased with substrate size; however, the highest values of richness per area and total cover increased towards the smallest substrates. Substrate size also positively influenced the cover of the perennial life forms hemiphanerophyceae and phanerophyceae, but do not on the cover of chamaephyceae. The perennial crustose Harveylithon samoënse showed a significant relationship with all variables increasing its cover towards small substrates in shallow, while the perennial erect Lobophora spp. are more abundant on large substrates at greater depths. Together these results showed that the substrate size was consistently the most important factor for algal diversity in unstable-bottom habitats.
... Variation in hydrographic conditions at the scales considered by our sampling design probably influence algal assemblages through the temporal variability and intensity of swells and storms, and the release of propagules from the water column (Micheli et al. 2005). Usually, water motion (1) enhances nutrient uptake by reducing or breaking the boundary layer, (2) removes epiphytes and waste products, and (3) allows algal stands to use light more efficiently by stirring their fronds, ensuring that no frond is either always shaded or always in the sun (Diez et al. 2003 and references therein). These mechanical advantages are accompanied by a continued mechanical stress that only morphologically adapted species can resist. ...
We conducted a mensurative survey to investigate spatial variability and the effect of wave exposure at a range of spatial scales including islands (100s of km apart), locations within islands (10s of km apart), and sites within locations (100s of m apart), on the composition, abundance and distribution of shallow water algal assemblages across subtidal hard bottoms of the Canarian Archipelago (eastern Atlantic). A multi-scaled hierarchical sampling design provided the framework for quantifying the variation among samples due to spatial scale and level of wave exposure. Randomly placed 50 × 50 cm squares were deployed in shallow rocky-reefs to assess community structure and dominance. Non-parametric multivariate techniques, as well as univariate tests, provided evidence to collectively suggest that shallow water algal assemblages differed between protected (leeward) and exposed (windward) shores, with a consistency of effects across islands, while different spatial scales were also involved in the variability and patchiness of these assemblages. In this sense, differences were clearly taxon and/or group-specific. In general, the presence and abundance of frondose fucoid species was greater on exposed shores than on protected shores, whereas turfalgae dominated along the protected shores of each island. Dissimilarities between islands with regard to the overall algal assemblage generally increased with the distance between islands. In particular, the presence and abundance of fucoid species was greater in the eastern islands, while turf
and bush-like algae increased in the western islands. The large-scale gradient of the oceanographic conditions in an east-to-west direction across the Canarian Archipelago provided a partial explanation for this observation although some inconsistencies were observed in the overall regional pattern.
... The morphology and survival of seaweeds is related to water flows created by waves or currents [18,46]. Thus, wave activity or wave-induced water motion is considered an important controlling factor in algal community structure and composition [47,48]. Munseom is located on the southern coast of Jeju Island, where it is directly open to the East China Sea. ...
Since 2015, troublesome masses of floating Sargassum horneri have been introduced via ocean currents and winds to the southwestern coastline of Korea, including Jeju Island. These massive mats have caused considerable damage to the aquaculture industry, tourism, and the marine ecosystem. Most previous studies of S. horneri have focused on cultivation, the development of gene markers, and photosynthetic activity, but few data on population dynamics are available. We investigated the population dynamics of native S. horneri off the southwestern coast of Korea with the aim of predicting the formation of golden tides. Populations at two sites had obligate annual life cycles. Thalli were recruited during the period September–November, grew during the period December–April, and senesced by July. This pattern reflected seasonal trends in water temperature. Specific growth rates and heights of the thalli at Munseom were significantly higher than those at Jindo. The greatest environmental difference between the two sites is probably the degree of exposure to wave action. Mortality density (thalli lost per unit area) in the Munseom population was highest during the period December–January (i.e., 2–3 months after recruitment) and in March. Most thalli in the Jindo population died off in July when water temperatures increased. The maximum average biomass of S. horneri thalli detaching from the substrata reached 1.6 kg fresh weight m–2 during January and March. Thus, large-scale drifting mats were formed by S. horneri detachment from the substrata. Despite the differences in space and environment between China and Korea, our findings will enable quantitative assessments of the overall floating Sargassum biomass in the East China and Yellow Seas.
... It is remarkable that most of the parameters selected for the model were the extreme ones, which highlighted its importance. Urms, Tm and Hs dependence plots supported the preference of C. baccata for sheltered areas, although it can tolerate semiexposed conditions (Dıéz et al., 2003;Méndez-Sandín and Fernández, 2016). The model captured its southern distribution in the Atlantic (García-Fernández and Bárbara, 2016), whose limits increase in the RCP 8.5. ...
There are evidences of how climate change is affecting seaweeds distribution and the ecosystems services they provide. Therefore, it is necessary to consider these impacts when managing marine areas. One of the most applied tools in recent years to deal with this are species distribution models, however there are still some challenges to solve, such as the inclusion of hydrodynamic predictors and the application of effective, transferable and user-oriented methodologies. Five species (Saccorhiza polyschides, Gelidium spinosum, Sargassum muticum, Pelvetia canaliculata and Cystoseira baccata)in Europe and 15 variables were considered. Nine of them were projected to the RCPs 4.5 and 8.5 for the mid-term (2040–2069)and the long term (2070–2099). Algorithms for each species were applied to generate models that were assessed by comparison of probabilities and observations (area under the curve, true skill statistics, Boyce index, sensitivity, correct classification rate), niches overlap (Schoener's D, Hellinger's I), geographical similarity (interquartile range)and ecological realism. Models built demonstrated very good predictive accuracy and sensitivity, without overfitting risk. A medium overlap in the historical and RCPs environmental conditions were obtained, therefore the models can be considered transferable and results accurate because only some isolated points were detected as outliers, corresponding to low probabilities. The areas of S. polyschides and G. spinosum have been identified to be dramatically reduced, meanwhile S. muticum and C. baccata were predicted to expand their range. P. canaliculata was expected to keep its sites of presence but with a decrease in its probability of occurrence. For all species it was remarkable the importance of hydrodynamic variables and parameters representing extreme conditions. Spatially predictions of the potential species and areas at risk are decisive for defining management strategies and resource allocation. The performance and usefulness of the approach applied in this study have been demonstrated for algae with different ecological requirements (from upper littoral to subtidal)and distributional patterns (native and invasive), therefore results can be used by marine planners with different goals: marine protected areas designation, monitoring efforts guiding, invasions risk assessment or aquaculture facilities zonation.
... Bolton and Anderson, 1990;Hoek, 1982), whereas the other factors are often more important at smaller, local scales (e.g. Dıez et al., 2003;Druehl, 1981;McQuaid and Branch, 1984). As environmental variables select for different species' traits, species respond differently to environmental changei.e. from being sensitive to tolerant or to directly benefitting from it (Foden et al., 2013). ...
Understanding how species' traits can shape winners and losers of environmental change can help resolve drivers of current community composition patterns and predict future drivers. Sedimentation is one of the main environmental stressors shaping coastal marine communities and tolerance of high sedimentation rates (e.g. via morphological variation) may allow for competitive dominance. In New South Wales, Australia, the abundance and range of the native green macroalga Caulerpa filiformis have increased over recent decades, apparently associated with sediment disturbance. We used field measurements to test hypotheses about morphological variability in C. filiformis in relation to local- and large-scale environmental variation in water depth, sediment cover and latitude. Using a lab experiment, we tested hypotheses about survival and morphological change under different sedimentation regimes. In the field, C. filiformis fronds were more elongated and less branched when a sediment veneer is present and when water depth increased (i.e. reduced light). At larger spatial scales, frond length and width decreased with increased latitude, but latitude was less important in explaining the variation C. filiformis’ length than were depth or sedimentation. Our lab experiment showed a high tolerance to sedimentation, aided by increased investment in vertical growth. This study shows that rapid morphological plasticity is a likely key attribute of the spreading native macroalga C. filiformis. We argue that having a broad environmental tolerance is key to define a species success under environmental change.
... Specimens of C. vermilara were scarce, as this species mainly occurs on the shore at shallow subtidal levels on the coasts of Spain (Ballesteros, 1989;Gorostiaga et al., 2004;Rojo et al., 2014), in contrast to the patterns observed in other regions, where C. vermilara was found widely distributed in the intertidal zone (Trowbridge and Farnham, 2004). Although C. decorticatum has previously been recorded in the study area (Gorostiaga et al., 2004), we did not find any examples of this species, which seems to be abundant in subtidal habitats (Díez et al., 2003). Furthermore, we selected semi-exposed locations on northern shores (Bay of Biscay) and western shores (Atlantic coast) (sites in the outer areas of the rias, in the latter case), to avoid confounding factors between longitudinal changes in C. fragile proportion and variations in wave exposure. ...
The green alga Codium fragile ssp. fragile (hereafter C. fragile) has long been assumed to outcompete and displace its native congeners via cryptic invasion. We analysed the population dynamics of the exotic C. fragile and native congeners and their relative abundance on intertidal shores in N-NW Spain. Our results did not support the existence of current competitive displacement by the exotic species. The presence of C. fragile was clearly seasonal, while the native C. tomentosum was more persistent throughout the year, due to a higher frequency of frond sprouting from perennial basal fragments. However, our results also indicated an increase in the proportion of C. fragile relative to native species towards inner areas of the Bay of Biscay, which was correlated with environmental gradients. The greater tolerance of C. fragile to environmental stress and its opportunistic abilities may favour establishment and spread of the species under a warming scenario.
... Thus, examination of long-term changes in macroalgal species composition of coastal communities can be used as an indicator of environmental change (Peckol 1983;Petsut et al. 2012;Titlyanov et al. 2015aTitlyanov et al. , 2016a. As seaweeds are the major primary producers dominating the benthos in many shallow seas, there have been numerous studies in different global regions on seaweed vegetation patterns and the effects of gradients in relevant environmental factors (e.g., Klöser et al. 1996;Diez et al. 2003). Recently, there has been an increase in studies documenting changes in the seaweed vegetation over a period of years (e.g., Piñeiro-Corbeira et al. 2016;Muguerza et al. 2017) or even decades (e.g., Pehlke and Bartsch 2008). ...
This study presents a long-term study (9 years) on seasonal changes in the marine macroalgal flora of Northern Taiwan in the southern East China Sea, from 2007 to 2015. Both spatial and temporal variations in the marine flora at six sites in the intertidal and subtidal zones were investigated. A total of 178 macroalgal species belonging to 4 phyla, 6 classes, 26 orders, 50 families, and 108 genera, were identified. The top five most abundant species were Ulva lactuca [Mean ± SD coverage (MC): 5.75 ± 9.44%], Pterocladiella capillacea (4.7 ± 4.76%), Marginisporum aberrans (2.49 ± 3.04%), Gelidium elegans (2.46 ± 4.05%), and Chondracanthus intermedius (1.58 ± 2.85%), accounting for 16.9% of the total macroalgal coverage. Non-metric multidimensional scaling analysis of all data revealed that the macroalgal assemblages fluctuated seasonally, with proportions of dominant species in the two habitats showing seasonal succession that was influenced by interplay of waters of the China Coastal Current from the west and the Kuroshio Current from the east. The physical differences of water depth and substrate in the intertidal and subtidal sites appeared to be an influential factor affecting the macroalgal composition. Cluster and index of seaweed importance analyses revealed the relative importance of certain species based on coverage and occurrence frequencies without requirements of other time-consuming measurements. Statistical analyses indicated significant variations in macroalgal assemblages among different sampling months. The macroalgal coverage and species richness have noticeably decreased during 2014–2015. Whether or not this phenomenon is a consequence of increasing seawater temperature needs further investigation.
... Fischer-Piètte, 1955;Díez et al., 2012;Martínez et al., 2012;Duarte et al., 2013;Vergés et al., 2016;Wernberg et al., 2016). While those at local scales have been associated to a large variety of impacts: (Furnari and Cormaci, 2009;Thibaut et al., 2005;Airoldi and Beck, 2007;Coleman et al., 2008;Mangialajo et al., 2008;Blanfuné et al., 2016b); overgrazing (Verlaque, 1987;Sala et al., 1998;Ling et al., 2014;Vergés et al., 2014); pollution (Cormaci and Furnari, 1999;Díez et al., 1999;Soltan et al., 2001;Díez et al., 2003;Sales et al., 2011); changes in nutrient concentration and turbidity in the water column (Sales and Ballesteros, 2009;Pinedo et al., 2013;Parravicini et al., 2013); and also the arrival of invasive species (Boudouresque, 2002;Cebrian and Ballesteros, 2007;Bianchi et al., 2014). In the Mediterranean, most of these works have focused on fucoid species, particularly Cystoseira spp., as they were the dominant habitatforming species along rocky shores at the beginning of the 20th century (Sauvageau, 1912;Feldmann, 1937;Molinier, 1960) and their loss has been widely reported (e.g. ...
Long-term ecological studies are crucial to understand how and why natural ecosystems change over time and space. Through a revision of historical data and a comparison with current in situ field data, we contribute to the understanding of how the Mediterranean coastal seascape has changed in the last decades. Here we describe the large decrease of the main habitat-forming species Codium vermilara along the Catalan coast (NW Mediterranean). We have analyzed data on presence/absence, abundance and biomass. Since the 70s–80s, when the species reached its highest abundances, the species has totally disappeared from 45% of the revisited sites, and showed a decrease in 95% of its abundance and 97% of its biomass. Codium vermilara has also shown a reduction in its depth range, from 30 to the first 20 m depth. This study highlights the importance of having historical data to detect and describe changes in ecological systems.
... Las características físicas de los ambientes suelen influir en la distribución y abundancia de las especies, ya que modulan la disponibilidad de alimento, la movilidad de las especies y la disponibilidad de O 2 , entre otros. Así, factores como la profundidad, la salinidad, el tipo de sustrato, la composición granulométrica y la intensidad de las corrientes tienen gran incidencia sobre los distintos miembros de las comunidades bentónicas (Hall 1994;Lenihan and Micheli 2001;Díez et al. 2003). Si bien este trabajo no tuvo como objetivo investigar las características físico-ambientales de los sitios de estudio, al seleccionar los bancos se tuvo especial cuidado en que fueran similares en relación a las características ambientales principales y que la diferencia entre ambos se concentrara sólo en la simulación del evento de pesca. ...
La almeja navaja (género Ensis) se explota en todo el mundo mediante una variedad de artes de pesca. Los impactos ambientales asociados a estas pesquerías incluyen cambios en las características físicas del sedimento y en la columna de agua, también efectos sobre las comunidades asociadas y sobre las mismas especies objetivo. El impacto producido depende principalmente del arte de pesca, del tipo de hábitat y de la intensidad de pesca. Los marisqueros del Golfo San José (Península Valdés, Chubut) emplean el hidrojet, una técnica que implica la inyección de agua en el sustrato para extraer navajas en distintos bancos. Si bien la explotación de este recurso en el Golfo San José aún es incipiente, resulta clave el estudio del impacto de esta pesquería para poder establecer medidas de manejo que se adecuen a la técnica empleada y al ambiente del Golfo, antes de que la pesquería se desarrolle a mayor escala. Así, el objetivo de este estudio fue evaluar de forma experimental el impacto de la pesca de la almeja navaja Ensis macha mediante el uso de la técnica hidrojet sobre las comunidades bentónicas asociadas a los bancos de esta almeja en el Golfo San José. Para ello, se comparó la composición de la fauna bentónica en dos bancos de navajas, uno con actividad extractiva y otro control, en el momento de la pesca y al año de realizada la actividad. Las comparaciones mostraron que en el tiempo inicial no se observaron diferencias entre el banco impactado y el control, mientras que luego de un año de realizada la actividad de pesca, las diferencias en la composición de las comunidades de ambos bancos fueron significativas. Así, el banco control se caracterizó por la presencia de poliquetos, anfípodos y estomatópodos, mientras que los moluscos bivalvos y gasterópodos fueron los grupos más representativos en el banco impactado. Los resultados hallados son útiles para sugerir medidas de conservación y gestión que eviten la degradación de la biodiversidad local.
... local oceanographic conditions, depth, sedimentation, pollutants) and species interactions (e.g. Díez et al., 2003;Martins et al., 2013;Sangil et al., 2014a;Bermejo et al., 2016). However, at larger biogeographic scales, studies mostly comprise general descriptions of biota, or analyses of presence/absence data, whilst abundance data are scant. ...
Shallow subtidal macroalgal communities in the North-eastern Atlantic archipelagos (Azores, Madeira, Canaries and Cape Verde) were studied in order to identify their spatial organization patterns and the main drivers of change. Fifteen islands 20 and 145 sites across 15º of latitude and 2 850 km were sampled. We found high spatial variability across the scales considered (archipelago, island and site). The structure of macroalgal communities differed among archipelagos, except between Madeira and the Canaries, which were similar. Across a latitudinal gradient, macroalgal communities in the Azores were clearly separated from the other archipelagos; communities in Madeira and the Canaries occupied an intermediate position, while those in Cape Verde appeared at the opposite end of the gradient. In the Azores, species with warm- 25 temperate affinities dominated communities. Cape Verde communities were in contrast dominated by tropical taxa, whereas in the subtropical Canaries and Madeira, there was a mixture of species with colder and warmer affinities. Apart from crustose coralline algae, the Dictyotales were the group with greatest cover; larger and longer-lived species were progressively replaced by short-lived species along a latitudinal gradient from north to south. The perennial species Zonaria tournefortii dominated the sea-bottom in the Azores, the semi-perennial Lophophora variegata in the Canaries and
30 the ephemeral Dictyota dichotoma in Cape Verde. We hypothesized that the differences among archipelagos could be explained by synergies between temperature and herbivory, which increased in diversity southwards, especially in Cape Verde. This was supported by the predominance of non-crustose macroalgae in the Azores and of crustose macroalgae in Cape Verde, as would be predicted from the greater herbivore activity. At the scale of islands and sites, the same set of environmental variables drove differences in macroalgal community structure across all the Macaronesian archipelagos.
... In addition, seaweeds may opportunistically colonise bare areas of horizontal reef surface between bouts of sand inundation, and then survive for extended periods even if they are later covered by sand (D'Antonio 1986). Seaweeds may grow tall enough to persist above the sand, or may be resilient enough to withstand inundation and/or abrasion (D'Antonio 1986;; Díez et al. 2003). Seagrasses such as the surfgrass Phyllospadix scouleri, which, like algae, are photosynthetic, may tolerate sand specifically because they are tall and can grow above the sand (Littler et al. 1983). ...
Distinctions are rarely made between vertical and horizontal surfaces when assessing reef community composition, yet physical differences are expected because of hydrodynamic differences and sediment accumulation on flat surfaces. As sand often diminishes biotic cover, we hypothesised that vertical surfaces will support a greater biomass but have lower diversity due to domination by a few species. To test this, we quantified sessile communities on vertical and horizontal surfaces at three sites in the Delagoa Bioregion on the east coast of South Africa. Community composition consistently differed: vertical communities were dominated by various filter feeders, especially the ascidian Pyura stolonifera, whereas those on horizontal reef comprised a mixture of filter feeders and various algae. The total number of species and all diversity metrics were significantly greater for horizontal reef surfaces. Contrastingly, Simpson’s dominance and biomass were significantly greater for vertical reef surfaces. Percentage cover of sand explained much of the variation in community composition whereas depth did not. Small-scale topographic differences in substratum orientation associated with differences in sand inundation will therefore influence both α and β diversity. Coastal developments and activities that alter sand movements and delivery to the coastal zone are therefore likely to have a profound influence on the maintenance and diversity of shallow subtidal communities.
... In intertidal and subtidal temperate and tropical rocky shores, the physical and biological factors are known to maintain the benthic marine organism assemblages' structure. Among the most important physical factors are sedimentation (Airoldi & Virgilio, 1998;Balata et al., 2011), wave patterns (Díez et al., 2003;Wernberg & Connell, 2008;Smale et al., 2011), tides (Metaxas & Scheibling, 1993), and water movement (Cheroske et al., 2000). ...
The study of the structure and dynamics of assemblages of benthic organisms has gained interest in recent decades because it can account for the influence of anthropogenic activities in the coastal zone and be incorporated into management and conservation plans. The region of Zihuatanejo, Mexico, has had an accelerated and unplanned urban development, negatively affecting coastal communities. However, studies on the structure and dynamics of algal assemblages, as well as some of the predominant physical factors in this region are scarce. The objective of this research was to carry out a preliminary study on the structure of macroalgal assemblages and their spatio-temporal variation in a depositional environment. The work was realized from June 2006 to December 2008 collecting randomly macroalgal samples and placing sediment traps on the bottom to characterize the deposition environment. The subtidal algal assemblages of the studied localities were predominantly turfs. The Detendred Correspondence Analysis showed that each locality had a particular species composition. The highest biomass was 37.82 ± 12.90 g dw m⁻² and the lowest of 0-7.86 g dw m⁻². The highest total sedimentation rate was 1818.10 ± 82.11 g dw m⁻² day⁻¹ and the lowest was 58.82 ± 8.75 g dw m⁻² day⁻¹. Significant differences were found in calcareous and articulated biomass, as well as in fine, coarse and total sedimentation rates among localities. The results obtained provide a basis for further research on the effects of sedimentation on the subtidal macroalgae assemblages of the study region.
... It is remarkable that most of the parameters selected for the model were the extreme ones, which highlighted its importance. Urms, Tm and Hs dependence plots supported the preference of C. baccata for sheltered areas, although it can tolerate semiexposed conditions (Dıéz et al., 2003;Méndez-Sandín and Fernández, 2016). The model captured its southern distribution in the Atlantic (García-Fernández and Bárbara, 2016), whose limits increase in the RCP 8.5. ...
An ecological classification at the local scale may be a useful tool for conservation planning and for the implementation of specific management programmes in a region. For this purpose, a methodology previously applied on a small scale has been adapted to classify the coast of Cantabria (N Spain). This methodology includes a physical classification and biological validation. The shoreline was divided into 1 km stretches, and the abiotic variables (sea surface temperature, photosynthetically active radiation, significant wave height and coastal morphology) were recorded for each stretch. A hierarchical classification was proposed, with a first level that encompassed a grouping of quantitative variables based on SOM and k-mean analysis and a second level that subdivided the previous groups according to the categorical variable ‘coastal morphology’. To validate the classification using biological data, cover of intertidal macroalgal species was obtained at 14 sites along the study area, and several statistical analyses were applied to test the ecological significance of this classification. Three physical units were obtained (western (W), central (C) and eastern (E) coast), based on abiotic variables. Each group was then subdivided into subunits according to its coastal morphology (cliffs or wave-cut platforms). A general agreement between the macroalgal distribution and physical units was accomplished. In the lower intertidal, Bifurcaria bifurcata and Halopteris scoparia dominated the western and central areas, whereas Corallina spp./Ellisolandia elongata and Gelidium spp. were most abundant towards the east. In contrast, throughout the middle intertidal, Corallina. spp./E. elongata were the dominant taxa. The classification system developed in this study completes a hierarchical framework for classifying the NE Atlantic coast, a promising approach that permits the application of the most suitable resolution in each case study that
could be applicable to a wide range of coastal areas.
... Loss of canopy forming macroalgae around the world is a major concern since it could trigger changes in the whole benthic ecosystem (Airoldi and Beck, 2007;Schiel and Lilley, 2011), especially in stressful environments (Watt and Scrosati, 2013). Gelidium corneum (Hudson) J. V. Lamouroux (Gelidiales, Rhodophyta) is a very important macroalga in the Cantabrian Sea (Díez et al., 2003;Gorostiaga et al., 1998;Rico and Fredriksen, 1996): it forms extensive stands on rocky shores off the Basque coast Gorostiaga, 1995), where it operates as an ecosystem engineer providing food and shelter to other organisms Bustamante et al., 2014). In recent decades G. corneum beds have suffered a considerable decline on several stretches of the Basque coast (Borja et al., 2013;Díez et al., 2012). ...
In recent decades a decline in the foundation species Gelidium corneum (Hudson) J. V. Lamouroux has been detected along the Basque coast (northern Spain). This decline has been attributed to several factors, but recent studies have found a relationship between high irradiance and the biochemical and physiological stress of G. corneum. Since physiological responses to changes in light occur well before variations in morphology, the present study seeks to use a size-class demographic approach to investigate whether shallow subtidal populations of G. corneum off the Basque coast show different frond bleaching, density and biomass under different irradiance conditions. The results revealed that the bleaching incidence and cover were positively related to irradiance, whereas biomass was negatively related. The effect of the irradiance level on frond density was found to vary with size-class, i.e. fronds up to 15 cm showed greater densities under high light conditions (126.6 to 262.2 W m− 2) whereas the number of larger fronds (> 20 cm) per unit area was lower. In conclusion, the results of the present study suggest that irradiance might be a key factor for controlling along-shore bleaching, frond density and biomass in G. corneum. Further research should be carried out on the physiology of this canopy species in relation to its bed structure and on the interaction of irradiance and other abiotic (nutrients, temperature, wave energy) and biotic factors (grazing pressure).
... These indicators are multiple, using a panel of techniques ranging from quadrat sampling to in situ visual estimation of the assemblages (e.g. Díez et al., 2003;Ballesteros et al., 2007;Orfanidis et al., 2011;Díez et al., 2012;Le Gal and Derrien-Courtel, 2015;Ar Gall et al., 2016;Blanfuné et al., 2016, and references therein). A further aim of seascape indicators using macroalgae is to provide information on the ecological status of the littoral zone (Cariou et al., 2013;Gobert et al., 2014). ...
... destruction of habitats, pollution, species introduction, overfishing, coastal aquaculture and global warming) (e.g. Steneck et al., 2002;Díez et al., 2003;Helmuth et al., 2006;Worm and Lotze, 2006;Airoldi and Beck, 2007;Hawkins et al., 2008;Wernberg et al., 2010;Schiel, 2011;Lamela-Silvarrey et al., 2012;Raybaud et al., 2013;Filbee-Dexter and Scheibling, 2014;Verg es et al., 2014). Different pressures act over time and in unison, with possible synergistic effects, affecting species, ecosystems and their ability to deliver ecosystem services. ...
In the Mediterranean Sea, Fucales, and in particular the species of the genus Cystoseira C. Agardh, are habitat-forming species dominating several benthic assemblages from the littoral fringe down to 70–80 m depth in the clearest waters. They generate high primary production involved in the maintenance of diversified trophic levels, they provide shelter, food, habitat and nursery areas to many species, and they are long-lived species that constitute a good model for studying human impact on species diversity. Cystoseira crinita Duby is a Mediterranean endemic cespitose species, living in shallow waters (0–5 m depth), in places with little wave action and high solar irradiance. To reconstruct the long-term patterns of change in its distribution along the French Mediterranean coast (French Catalonia, Languedoc, Provence, French Riviera and Corsica), all the historical data (published articles, unpublished reports and herbarium vouchers) collected since the 18th century were searched and analysed. To assess the current status of the species, several field surveys were conducted between 2010 and 2016 by snorkelling and SCUBA diving. Cystoseira crinita is currently extinct in French Catalonia, near-extinct in Languedoc and western Provence, and functionally extinct on the French Riviera coast, while the eastern Provence and Corsican populations have remained stable. The main probable causes of decline are habitat destruction and overgrazing by herbivores.
... At higher scales (e.g. at a Regional scale) factors such as exposure to wave action, tidal range, salinity and nutrients may play a major role in the distribution and structure of communities (Kautsky & van der Maarel, 1990). However, at a local scale some of these variables do not vary significantly; therefore, other factors, such as geomorphological characteristics and bathymetry, seem to affect species distribution (Schoch & Dethier, 1996;Díez et al., 2003;Chappuis et al., 2014;Ramos et al., in press). The successful protection of marine diversity, the assessment of anthropogenic impacts and the restoration of altered ecosystems rely largely on the understanding of processes and factors that structure biological assemblages (Chapman, 1999). ...
Ecological classification of coastal waters has become increasingly important as one of the basic issues in the biology of conservation. Management and protection of coastal areas take place at different spatial scales. Thus, proper classification schemes should integrate equivalent information at various levels of definition in order to show its feasibility as a useful tool for assessment of coastal environments at the required scales. In this work, a global approach applied to the classification of the NE Atlantic coast is analysed in order to discuss pros and cons regarding different conceptual and technical issues for effective implementation of such a management tool. Using the hierarchical system applied at three different geographic scales: Biogeographic (NE Atlantic coast), Regional (Bay of Biscay) and Local (Cantabria region), five different topics were considered for debating strengths and weaknesses of the methodological alternatives at those spatial scales, using for validation the rocky shore macroalgae as a representative biological element of benthic communities. These included: (i) the spatial scales; (ii) the physical variables and indicators; (iii) the classification methodologies; (iv) the biological information; and (v) the validation procedure. Based on that analysis, the hierarchical support system summarized in this paper provides a management framework for classification of coastal systems at the most appropriate resolution, applicable to a wide range of coastal areas. Further applications of the physical classification for management of biodiversity in different environmental scenarios are also analysed.
... Previous studies have showed that this information can be useful in the selection of suitable biomonitors. The use of these functional groups has already been tested to water quality (Orfanidis et al. 2001) and more recently to detect pollution (Díez et al. 2003), where ESG I prefer the clean areas and ESG II the impacted areas. Consequently, it seems more appropriate to choose an opportunist species, due to their ability to resist to anthropogenic stress. ...
Arsenic is a widely distributed element in marine ecosystems. The main anthropogenic sources of this contaminant are domestic and industrial wastewaters, and since it can be harmful to humans even at low concentrations, it has been ranked as one of the top hazardous substances. Therefore, the analysis of arsenic is an essential task to assess the potential environmental and human health risk associated with sewage discharges. The accumulation of total arsenic on intertidal rocky shore macroalgae exposed to contaminated sewage discharges was measured in five macroalgae species (Asparagopsis armata, Codium sp., Plocamium cartilagineum, Saccorhiza polyschides and Ulva sp.). Differences in the concentrations of arsenic were examined in the seawater and in the macroalgae species. The results showed significantly higher concentrations of arsenic near the sewage discharges in all the species except S. polyschides. Although the information obtained from total arsenic determination is not enough to assess the toxicological risk in the environment, this paper gives an important contribution on contamination risks and helps in choosing potential good biomonitors.
Recent studies suggest that the lithological properties of hard substrates play an important role in influencing the diversity and structure of marine assemblages involving macroalgae, sessile organisms and vagile animals like heterobranchs gastropods and fishes. The present study aims at exploring whether the influence of different substrates (limestone vs granite) could drive the occurrence of different vagile groups (crustacean decapods, echinoderms and fishes). The study was carried out at the "Tavolara-Punta Coda Cavallo" Marine Protected Area (NE Sardinia, Mediterranean Sea) where substrates of different lithology, namely granites and limestones, occur on a local spatial scale. The diversity and the abundance of 16 vagile species (four crustaceans, seven echinoderms and five fishes) were investigated by the analysis of photographs (2352 images) collected in 20 sites (10 limestones and 10 granites), between 30 and 50 m depth. Statistical analyses showed a clear-cut separation between the assemblages assessed on the two lithological substrate types, with assemblages on granites that were tightly grouped and those on limestones more dispersed. The total species richness did not significantly vary between limestones and granites. Galathea strigosa and Marthasterias glacialis were exclusively recorded on granites, while Palinurus elephas, Scyllarides latus, Arbacia lixula, Ophidiaster ophidianus and Serranus scriba were exclusively found on limestones. The observed patterns could be partially explained by multiple factors related to lithology: i) the different availability of preferred food sources, potentially influenced by substrate type; ii) the site geomorphology, that could provide different dens and refuges (in terms of quantity and types of shelters) suitable for different species; iii) the colour of different substrates enhancing the mimicry of different species according to their livery and camouflage ability. Our and literature data suggest that the substrate type in rocky reefs could interact with other environmental factors (i.e., light intensity related to depth) in shaping the structure of rocky-reef assemblages.
In this study, the climate change, tsunami and biodiversity for 336 km coastline endangered at the South China Sea was investigated with the review for the past, current and prediction models for the future. The hydraulic study of the coastal area was conducted using a well-established 2D numerical model suite Delft3D. The study revealed that the generated earthquakes at the convergence zone in the last century are small (Mw7.3), the possibility that a megathrust earthquake event in the SCS basin occurs in the future. The study area comprises a narrow strip of vegetation notably dominated by Casuarina equisetifolia with other coastal plants. Mangrove forests are found along the coastline and estuaries that are overlaid with marine alluvial soils. The current paper is the first comprehensive study of the South China Sea, and the findings increase the awareness among the public to understand the risk associated with environmental pollution.
Estimating spatial patterns of variability in coastal marine priority habitats may allow to plan monitoring programs and impact evaluation studies and to optimize sampling designs in environmental investigations. In this study the spatial variability of the vertical distribution (18 m, 23 m, 28 m, 33 m, and 38 m of depth) of coralligenous cliff assemblages was estimated in three marine biogeographic areas of the Mediterranean Sea: the Sardinia Sea, the Tyrrhenian Sea and the Bonifacio Strait. Sampling sites were selected in the West, North, and East coast of Sardinia, all in pristine conditions (far from any anthropogenic sources of influence and in highly oligothrophic water). Important variations among areas in the vertical zonation of the coralligenous cliffs have emerged, especially at the shallower depths, and the dominant taxa have been highlighted. Despite these unconsistencies, a common increase in the number of taxa/groups per sample was found with depth. Thermal environment and hydrodynamics have been discussed as the most likely important drivers of such variability. Overall, these data support the hypothesis that coralligenous cliff assemblages unaffected by local anthropogenic disturbance may be relevantly different in structure and indicate that the lack of gorgonians and bryozoans (commonly used as ecological indicators) is not necessarily a sign of local human impact, as it may be the result of biogeographic patterns.
Coastal ecosystems can provide significantly high ecosystem services via various processes. Tropical and/or subtropical coastal ecosystems are constituted by reef-building corals, macroalgae, and seagrasses. The study was conducted in a subtropical coastal area, Okinawa Island, Japan, where macroalgal beds are distributed. Since few studies have focused on the macroalgal community compared to corals in the study area, the relationship between macroalgal (especially Sargassaceae species) distribution and environmental factors were evaluated. Environmental parameters used in the analysis were obtained by field observation, geographic analysis, satellite observation of water quality, and numerical simulation of wave height. Sampling was conducted mainly between May and August in 2018 and 2019, and 31 sampling stations were established along the coastline of Okinawa Island. Though hermatypic corals occurred in most of the stations, the distribution of Sargassaceae was spatially skewed from the southern and central part of the east coast. Canonical correspondence analysis (CCA) was applied to obtained environmental variables and presence–absence data on macroalgae (Sargassaceae), corals, and seagrasses. CCA results indicated that the geographical setting (openness) and wave exposure in winter are the primary factors determining the macroalgal distribution, whereas nutrient (dissolved inorganic nitrogen, phosphorous, and silicon) concentrations at each sampling occasion were not significant factors. Since coastal ecosystems are threatened by both local and global impacts, elucidation of the major mechanism limiting Sargassaceae distribution is significant for coastal ecosystem management, here we use Okinawa Island as an example.
A distortion of coastal communities has been reported along the European Atlantic in recent years. In NW Spain, the lack of studies focusing on long-term changes was resolved when several common perennial seaweeds were shown to have diminished in occurrence between 1998/99 and 2014. To ascertain whether their decline reflected a genuine
long-term trend, the same network of monitoring locations and the same set of perennial seaweeds was re-surveyed in 2018. Contrary to our expectations, the average number of species per site increased in semi-exposed and semisheltered locations to become statistically indistinguishable from 1998/99 estimates, and it is speculated that growingly
wave power may have displaced some species typical of wave exposed conditions to sites formerly regarded as semiexposed/semi-sheltered. Nevertheless, site occupancy rates continued to be below 1998/99 estimates for several seaweeds, and warming, both from rising average temperatures and from more frequent and intense marine heatwaves in autumn, seems a plausible explanation for their decline. The benefits of routinely monitoring a network of fixed stations are discussed.
The brown alga Cystoseira amentacea (Phaeophyceae, kingdom Stramenopiles) constitutes an extensive belt in the shallowest horizon of the infralittoral (the infralittoral fringe), in the Mediterranean Sea. Hydrodynamic modelling was used to infer connectivity between populations of C. amentacea of the Bay of Marseille (Provence, France, NW Mediterranean) and to test the correlation between genetic and hydrodynamic connectivity. We genotyped 183 individuals from six populations at six microsatellite loci. Current fields were computed at a fine resolution by a 3D numerical model simultaneously utilizing the local winds, the Rhone River inputs and offshore circulation. The Lagrangian trajectories of the propagules (zygotes, or rafts) were computed with the ICHTHYOP software, for both NW and SE strong wind forcing (11-12 m·s⁻¹). Cystoseira amentacea displayed a strong and significant genetic structure, not correlated with the geographic distance, i.e. a lack of isolation by distance (IBD). The pairs of sites with the lowest FST were those connected by the current patterns. The time needed for a zygote or a raft to travel from one location to another ranged from 4 to 18 h (i.e. within the survival time of a zygote) and for distances of up to 23 km. Despite the very low dispersal capability of the zygotes, long-distance dispersal is therefore possible. Several non-exclusive processes can account for the genetic structure of C. amentacea populations, such as step-by-step local dispersal, long-distance dispersal of zygotes and rafts by currents, during storms, and the "priority effect", i.e. the importance of the timing of arrival of the propagules.
The French Riviera is one of the Mediterranean areas that has been longest and most thoroughly impacted by human activities. Fucales are long-lived, large-sized brown algae that constitute a good model for studying human impact on species diversity. We gathered all historical data (literature and herbarium vouchers), since the early 19th century, to reconstruct their distribution. The current distribution was established from a 7-year (2007-2013) survey of the 212-km shoreline (1/2 500 map), by means of boating, snorkelling and scuba diving. Overall, 18 taxa of Cystoseira and Sargassum have been reported. Upon comparison with historical data, 5 taxa were no longer observed (C. elegans, C. foeniculacea f. latiramosa, C. squarrosa, C. spinosa var. spinosa and S. hornschuchii) while C. jabukae, previously unrecorded, was observed. In addition to these taxa, probably extinct at a local scale, some taxa had suffered a dramatic decline (C. barbata f. barbata, C. crinita, C. spinosa var. compressa and S. acinarium) or become nearly extinct (C. foeniculacea f. tenuiramosa). Three of them, which played in the past significant functional roles in coastal communities, can be considered as functionally extinct. Possible causes of decline and local extinction are discussed. A similar situation has already been reported, although at a much more local scale, in a variety of Mediterranean localities. The question therefore arises about the status of Fucales species in the Mediterranean: are some species on the brink of extinction? Is their extinction at the scale of the French Riviera the harbinger of their extinction Mediterranean–wide?
An exploration of historical data suggested that eutrophication patterns might drive long-term fluctuations in Cystoseira populations along the west Istrian Coast (northern Adriatic Sea, Croatia). The regimes of northern Italian rivers, which flow approximately 100km west of the study area, mainly modulate the eutrophication levels of the northern Adriatic Sea. A regression of Cystoseira populations from the 1970s through the 1990s corresponded to increased levels of eutrophication in the study area. During the late 1990s, the density of sea urchins, which are efficacious macroalgal predators, decreased, likely due to an intense formation of pelagic mucilage aggregates that resulted in mass mortality episodes of macrozoobenthic species. During the 2000-2013 period, an oligotrophication of the northern Adriatic formed the basis for the recovery of Cystoseira taxa, whose abundances from 2009 to 2013 were similar to those characterising the most flourishing Mediterranean Cystoseira assemblages.
The depositional environment over a turf assemblage of the rocky shore south of Livorno was studied from April 1992 to September 1993 by means of sediment traps positioned 50 and 200 cm above the turf surface. Changes in environmental conditions and in the intensity of terrestrial erosion and wind-wave resuspension of bottom sediments played a major role in controling both the magnitude of sediment deposition and the nature of sedimented material, while limited responses to seasonal patterns of sedimentation of phytoplanktonic material were found. Mean rates of sediment deposition fluctuated between 1.6 and 52.4 g m(-2) d(-1), and the amount of trapped material decreased with distance from bottom, reflecting intense sediment resuspension and movement over the algal turf. The material sedimenting was mostly composed of small-size (<200 pm) inorganic particles, and the organic material was characterized by the presence of highly degraded detritus. Besides faecal pellets few recognizable structures were found in the traps, such as charcoal fragments which probably originated from extensive burning of the coastal vegetation. Considerable variations in the intensity of the depositional environment over the algal turf were evident: the maxima sediment deposition and movement occurred in autumn and were related to heavy rainfall and wind-wave action, while in the summer the algal turf was generally free from sediment smother and scour. The ecological significance of these quantitative and qualitative temporal fluctuations is discussed, and the possible long-term impact of fire deforestation and increased soil erosion on turf structure and composition is hypothesized.
The distribution patterns of dominant macrophytes (Gelidium sesquipedale, Saccorhiza polyschides and Laminaria ochroleuca) in relation to local abiotic conditions (depth, sediment loading and substrate topography) were investigated in a commercial stand of G. sesquipedale off Cape Espichel, Portugal, using principal component analysis. Observed patterns were analysed using multiple regression models to assess the strength of the relationship between G. sesquipedale and the different biotic and abiotic factors. Both multivariate and multiple regression analyses revealed significant positive relationships between G. sesquipedale cover and substrate slope, and negative relationships among G. sesquipedale, sediment loading and S. polyschides density. The main effects of these variables on the abundance of G. sesquipedale are of the same relative magnitude. Within the depth range studied (0 to 18 m), S. polyschides abundance was the only variable correlated with depth. The only interaction significantly correlated with G. sesquipedale local distribution was that between L. ochroleuca density and depth. Data suggest that steep slopes and reduced sediment loading favour G. sesquipedale development. On the contrary, S. polyschides dominated in shallow zones with low slope surfaces and high sediment loading. L. ochroleuca by itself was not significantly correlated to the distribution of G. sesquipedale, but its interaction with depth suggests that at greater depths it dominates G. sesquipedale. This is supported by analysis of the correlations between the 3 species in shallow versus deeper zones. Potential mechanisms are discussed for the significant relationships found, and testable causal hypotheses are suggested.
Seasonality and reproductive phenology of marine macroalgae were investigated from June 1992 to June 1993 on a subtidal rocky shore south of Livorno (Western Mediterranean Sea) that was characterized by high rates of sediment deposition and movement. The assemblage was strongly dominated by a persistent filamentous turf of Polysiphonia setaceq that covered the rocks and encrusting algae, whlle Halimeda tuna was the only abundant erect species. During the year the thickness of the turf fluctuated in response to changes in weather conditions and in the intensity of depositional environment. Conversely, the composition and lhe structure of the assemblage remained rather constant, and its diversity was quite low. It is suggested that both sediment stress and competitive interactions among P. setacea and erect species might play an important role in maintaining and structuring the algal turf in the study area
The importance of the shape of a species response curve to an environmental gradient is reviewed. The implications for vegetation theory, ordination methods, species as indicators of environmental conditions, predicting species distribution from surveys and simulation models of climatic impact on vegetation are examined. A beta-function V = k (x - a)alpha . (b - x)gamma is used to model species response curves using generalized linear modelling (GLM). Two hypotheses are tested; (1) that response curves differ significantly from a unimodal symmetric (Gaussian) shape and (2) that the direction of skew is a function of species position along the gradient. Nine eucalypt species are modelled using GLM with a beta-function fitted for mean annual temperature. Six other environmental variables and factors are considered in fitting the statistical models; mean annual rainfall, mean monthly solar radiation, topographic position, lithological type, nutrient index and rainfall seasonality. All nine species are significantly skewed in response to temperature. The direction of skew is positive when a species optimum temperature falls below 11.5-degrees-C and negative for species with optimum above. These results indicate that current vegetation analyses which require the modelling of species response curves, or assumptions about the shape of the response, require reassessment.
The brown alga Ascophyllum nodosum is a dominant rocky intertidal organism throughout much of the North Atlantic Ocean, yet its inability to colonize exposed or denuded shores is well recognized. Our experimental data show that wave action is a major source of mortality to recently settled zygotes. Artificially recruited zygotes consistently exhibited a Type IV survivorship curve in the presence of moving water. As few as 10, but often only 1 relatively low energy wave removed 85 to 99% of recently settled zygotes. Increasing the setting time for attachment of zygotes (prior to disturbance from water movement) had a positive effect on survival. However, survival was significantly lower at high densities, and decreased at long (24 h) setting times, probably as a result of bacteria on the surface of zygotes. Spatial refuges provided significant protection from gentle water movement but relatively little protection from waves.
Oceanographic conditions in spring and summer, caused by northerly-easterly winds of medium and low intensity, in the Bay of Biscay seem to induce good levels of recruitment to the anchovy population. This wind regime produces upwelling conditions with, generally, low degrees of turbulence. Indices of upwelling and turbulence were built and proved significantly correlated with an index of annual recruitment of anchovy (p<0.0001). Both physical parameters explain about 70% of the variance in the index of recruitment of the Bay of Biscay anchovy. The likely explanations for this relationship are outlined and discussed in the light of the current hypotheses about the processes determining recruitment of marine populations. Enhancement of the productivity and increased availability of food to the early life history stages of anchovy seem to be the main consequence of the prevalence of weak upwelling conditions in this area during spring.
Crusts and tufts occur within the boundary layer and thereby may avoid mechanical stress caused by flow. The more tolerant semi-erect forms can be divided into mucilaginous and non-mucilaginous filaments as well as tissue-like thalli. Twelve taxa from these groups occur at a wide range of current velocites (mean 24-58 cm.s-1). There is a significant increase in strength of these forms in a gradient from tufts (12 ± 7 kN.m-2) to mucilaginous filaments (530 ± 160 kN.m-2) to nonmucilaginous filaments and tissues (1400 ± 400 kN.m-2). In terms of breaking extension, no consistent trend is observed among the different morphologies; the range is 11.3-29.2% beyond the original length. Sirodotia suecica produces the least increase in drag force with increasing flow and thus the lowest E value (-1.27) whereas the large mucilaginous species Batrachospermum boryanum and B. virgatum show the highest drag forces and E values (-0.45 to -0.33). Almost a 10-fold range in estimated current velocities is required to break apart the freshwater red algae tested. -from Authors
Sublittoral communities of macroalgae from the Abra d e Bilbao and its surrounding area, which are affected by pollution, were studied in 1984 and 1992. Statistical cluster analysis applied to a network of 230 quadrats distributed along 7 transects resulted in 4 structural levels of community, depending on the pollution gradient. These levels are defined by algal cover, vertical layering and the predominant morphology of the species forming the communlty. Sedimentation, turbidity and water toxicity are the principal destabilizing factors among the phytobenthic communities Species with simple morphology, mainly ceramiaceous algae (Ceramium diaphanum, Calllthamnion neglecturn, Antithamnionella spirographidis. Pterotharnnion plumula, Anotrichium furcellaturn, Compsothamnion thuyoides), sciaphilous (Mesophyllum lichenoides, Zanardjnia prototypus, Rhodymenia coespitosella, Drachiella minuta, Erythroglossum laciniatum, Hypoglossurn hypoglossoides) and those resistant to sedimentation (Pterosiphonia pennata and Champia parvula) are the most widely found species in severely polluted settings. Species such as Gelidium sesquipedale, Heterosiphonia plumosa, Callible-phans ciliata. Halopitys incurvus, Djctyopterjs polypodioides and Halurus equisetifolius are species typically found at the reference site and are good indicators of unchanged environments. Pterosipho-nia complanata, abundant at the reference site, took the place of G. sesquipedale in those sites farthest from the source of pollut~on Ord~nation and classification analyses detected changes in flora after 8 yr, pointing toward a recuperating process. The improvement consisted of an increase in algal cover along with a decrease in ceramiaceous algae and a greater complexity in communlty stratification. This recovery was directly related to a decrease in industrial activity and closure of the mineral washeries, as well as the establishment of urban wastewater-treatment plants for various municipalities.
In conditions of low water motion (–1), the availability of essential nutrients to macroalgae, and thus their potential productivity, may be limited by thick diffusion boundary-layers at the thallus surface. The ability of macroalgae to take up nutrients in slow moving water may be related to how their blade morphology affects diffusion boundarylayer thickness. For the giant kelp, Macrocystis integrifolia Bory, morphological measurements indicate that blades of plants from a site exposed to wave action are thick, narrow and have a heavily corrugated surface. In contrast, blades from a site with a low degree of water motion are relatively thin, with few surface corrugations and large undulations along their edges. The aim of our work was to test the hypothesis that morphological features of M. integrifolia blades from a sheltered site allow enhanced inorganic nitrogen uptake at low seawater velocities compared to blades with a wave-exposed morphology. The rate of nitrate and ammonium uptake by morphologically distinct blades of M. integrifolia, from sites that were sheltered from and exposed to wave action, were measured in the laboratory at a range of seawater velocities (0.01 to 0.16 ms–1), between March and May 1993. For both sheltered and exposed blade morphologies, nitrate and ammonium uptake rates increased with increasing seawater velocity, reaching a maximum rate at 0.04 to 0.06 ms–1. Uptake parameters V
max (maximum uptake rate) and U
0.37 (the velocity at which the uptake rate is 37% of the maximum rate) were estimated using an exponential decay formula. These parameters were similar for both blade morphologies, at all seawater velocities tested. Additional measurements suggest that the nitrogen status of M. integrifolia blades from wavesheltered and exposed sites were similar throughout the experimental period, and thus nitrogen status did not affect the rate of nitrogen uptake in these experiments. on the basis of these results, we conclude that blade morphology does not enhance nitrogen uptake by M. integrifolia in conditions of low water motion. Potential effects of diffusion boundary-layers on kelp productivity are discussed.
Canonical correspondence analysis (CCA) is introduced as a multivariate extension of weighted averaging ordination, which is a simple method for arranging species along environmental variables. CCA constructs those linear combinations of environmental variables, along which the distributions of the species are maximally separated. The eigenvalues produced by CCA measure this separation.
As its name suggests, CCA is also a correspondence analysis technique, but one in which the ordination axes are constrained to be linear combinations of environmental variables. The ordination diagram generated by CCA visualizes not only a pattern of community variation (as in standard ordination) but also the main features of the distributions of species along the environmental variables. Applications demonstrate that CCA can be used both for detecting species-environment relations, and for investigating specific questions about the response of species to environmental variables. Questions in community ecology that have typically been studied by ‘indirect’gradient analysis (i.e. ordination followed by external interpretation of the axes) can now be answered more directly by CCA.
The storm-related mortality rates of adult Macrocystis pyrifera in a Southern California giant kelp forest were determined over several winter storm seasons and compared with the hydrodynamic attributes of the most energetic storms. The data include stormy and relatively benign years and an exceptional storm which resulted in almost total destruction of a major Macrocystis forest. High orbital velocities (associated with large, high frequency waves), the presence of breaking waves, and entanglement by drifters were found to increase mortality through stipe breakage or holdfast failure. Longshore variability in wave intensity was found to affect kelp mortality rates. The data suggest that wave breaking may be an important factor in determining the inner boundary of the kelp bed.
A new method of evaluating seaweed quantities has been worked out and practised during the last five years in Norway. It is founded on the two-stage sampling technique first involving a selection of primary units and then a subsampling of secondary units from each selected primary unit. The districts were divided into squares (= primary units) with sides 0.25 nautical mile (463 m). These squares were completely registered, counted, and classified by means of Admiralty Charts. A random selection of them was made. These were visited, their littoral zone completely and accurately mapped by tachymeter measurements, and random samples (= secondary units) of their seaweed vegetation cut and weighed. Estimates of means/square and of total seaweed tonnage in the district could then be calculated together with their standard errors. Stratification of squares according to shore length and degree of exposure to waves served to reduce standard errors and to locate harvestable quantities.
As part of a multidisciplinary study of the pollution of the Nervion estuary in the area of Greater Bilbao, surveys were carried out on the causes and extent of pollution in the freshwater and tidal reaches of its tributaries. Pollution of the freshwater tributaries continued to the tidal limit, due to the entry of sewage and industrial wastewater. The types and quantities of pollutants are given. It was established that the treatability of effluents from industrial premises could be determined satisfactorily in laboratory scale activated sludge units. It was anticipated that preliminary screening tests could be carried out to determine treatability using manometric techniques.
Increasing amounts of various types of wastes and pollutants including nutrients enter the coastal waters via rivers, direct discharges from land drainage systems, diffuse land runoff, dumping and via the atmosphere. This has led to coastal eutrophication and in extreme cases to hypertrophication. Until recently, coastal eutrophication and the resulting effects on marine macrophytes were mainly treated as local short-term problems. This book systematically covers the entire coastline of Europe, documenting the effects of eutrophication on the marine benthic vegetation.
Seven different data types obtained from the same set of field quadrats, and comprising qualitative, frequency, percentage cover and biomass records together with simple transformations of certain of the measures, are compared in respect of both their numerical properties and ecological performance under analysis. The numerical comparisons include raw data correlations, and hierarchy and group comparisons of the data classified under a polythetic divisive technique; the combined results of the comparisons have also been subjected to a principal components analysis to aid interpretation. The ecological assessment is made on the basis of the general usefulness of the different classificatory groupings obtained, and on the extent of retrieval of information in a `control' hierarchy erected subjectively for the test-area from general ecological experience. The results of the numerical comparisons show that the extent to which differences in floristic composition are masked by differences in overall bulk of plant material between the quadrats is the main discriminating feature between the different data types. An important secondary feature is the nature and extent of constraints upon the measures. A distinction is made between (a) unbounded data, where the measures are free to vary without constraint across both the quadrats and the species, (b) partially bounded data, where the measure is bounded for each species in a quadrat, but each quadrat total is unbounded, and (c) bounded data, where the quadrat total itself is constrained to a ceiling value and the species values can vary only within that constraint. The ecological assessment suggests that quantitative measures which are sufficiently constrained to allow quantitative differences to operate primarily within a framework of floristic diversity, rather than vice versa, are likely to be the most generally useful for ecological work concerned with plant/habitat relationships. On the other hand, partially bounded measures which are species-constrained, such as frequency, may prove too similar to qualitative data in their performance to warrant the extra time and effort spent in collecting such data.
The work reported in the first paper of the series (Smartt et al. 1974) is extended to encompass thirteen data types, comprising qualitative data, two frequency measures, four estimates of percentage cover with and without an arcsin transformation, and an estimate of bulk with and without proportionalization. These are tested under more searching ecological conditions than those offered by the previous test-community. The qualitative and quantitative components of the raw data matrices are examined, leading to comparisons of the relative performance of the different data types under a given classificatory technique. Finally the results of the classifications are assessed against an independent classification of relevant habitat factors. The main findings are that (i) qualitative data provide the best ecological groupings in terms of the major habitat divisions, but quantitative data can become important at a lower level; (ii) for quantitative data, more interpretable ecological results are likely to be obtained from direct measures of the amount of plant material, suitably transformed, than from frequency measures; (iii) since the main function of the transformation is to increase the proportional contribution of subsidiary but discriminating species, such transformations should be sought in monotonic functions which implement such increases without destroying the rank relationships of the individual records; and (iv) approximations in methods of field recording, unless exceptionally crude, have less effect on the results than changes in the nature of the measure.
The distribution of Himanthalia elongata has been surveyed along the north-east coast of England. The species grows on a wide variety of geological substrata where they are weathered into horizontal ledges near l.w.s.t. Laboratory culture experiments have shown that a slight decrease in salinity decreases the percentage of germination and below a salinity equal to 50% sea water no germination occurs. Very few zygotes germinate in total darkness. With increased light intensity at 10 °C the highest percentage germination was obtained at approximately 6000 lux. Maximum growth of young germlings was obtained at about 10 °C and 1272 lux under a hour light/ dark period. Silt appears to be a major factor inhibiting colonization along stretches of the north-east coat. It acts by cutting down the amount of light received by the zygotes and also it forms a substratum of fine particles to which the zygotes, with their highly specialized mode of adhesion, are unable to become attached.
The invasive brown seaweed Sargassum muticum was first recorded in northern Spain in the 1980's. The species is now patchily distributed in localities that differ in wave-exposure and is most abundant in sheltered areas. A transplant experiment was done on a local scale to test the ability of S. muticum to persist and grow on wave-exposed shores. One month after transplantation, plants moved to exposed areas suffered a high percentage of breakages (>80%). When only plants without damage were considered, those transplanted to exposed areas exhibited a mean elongation rate significantly less than those on the sheltered shore. The lower rate of elongation in the absence of any apparent injury suggests a grade of phenotypic response of S. muticum to changes in the physical conditions. Nevertheless, the low tolerance exhibited by this species to mechanical stress indicates that its distribution may be limited by physical conditions in wave-exposed environments.
The effects of the discharge of secondary-treated sewage effluent on intertidal macroalgae were assassed over an eight year period from 1980 to 1988. During this period effluent flow increased by 30% to 290 MI per day. A number of sites at varying distances from the outfall were monitored and the results compared with a previous study carried out in 1975-6 before and after discharge commenced. In the present study, fewer species were recorded at sites close to the outfall than at more distant sites, and loss or reduction of the canopy-forming brown alga Hormosira banksii resulted in a community with less vertical stratification near the outfall. Algal turfs, consisting of Gelidium pusillum, Ulva rigida and Ceramium flaccidum, occurred on the higher intertidal reefs adjacent to the outfall, and dense turfs of Corallina officinalis occurred on the wetter, lower intertidal reefs near the outfall. The observed changes in macroalgal communities were consistent with the effluent being transported in a southeasterly direction along the coast, with sites near and southeast of the outfall affected and northwestern sites apparently unaffected. Cluster analyses of site area/times using Sorensen's and Czekanowski's coefficients of similarity showed differences in the pattern of association but reinforced the finding that communities at sites southeast of the discharge point are affected by the effluent. Cluster analyses were useful in assessing the changing relationships between site areas over time. Factors believed to be important in structuring the algal communities include distance and direction from the outfall, direct effects of effluent on both plants and animals, height of the site area relative to the low water mark, exposure to wave action, abundance of certain animals which can displace the algae, grazing effects of intertidal invertebrates and fish, and climatic variations. Continued effluent discharge during the present study probably resulted in a further reduction in large brown algae at the Cape Schanck site, and a gradual reduction in the abundance of epilithic algal turfs at the effluent-affected sites. However, the relative abundance of species in epilithic turf communities at effluent-affected sites remained fairly stable over the study period.
The lower rocky intertidal zone of many moderately exposed and exposed shores in the Gulf of Maine, USA, is co-dominated by two species of red macroalgae, Chondrus crispus Stackhouse and Mastocarpus stellatus (Stack. in With.) Guiry. These species are anatomically, morphologically, ecologically and phylogenetically similar. We quantified: 1.(1) mechanical properties of the stipe; and2.(2) flow forces on the stipe relative to thallus area and biomass of these species, to determine mechanical and morphological characteristics that could explain the greater winter dislodgement of C. crispus thalli in mixed stands. Although stipes of both species broke at the same mean force, C. crispus stipes were relatively thick, weak and extensible compared to the relatively thin, strong and stiff stipes of M. stellatus. Risk of breakage increased with size in both species because: 1.(1) their stipes weakened with increasing cross-sectional area; and2.(2) cross-sectional area of the stipe failed to increase in linear proportion to frond area. Drag on C. crispus thalli of > 3 g fresh weight was greater than on M. stellatus of the same biomass, whereas drag on smaller fronds ( < 3 g fresh weight) of the two species was similar. Drag on large C. crispus thalli was greater mainly because they exhibit greater surface area for a given biomass than do large M. stellatus. Dislodgement by hydrodynamic forces has more severe ecological consequences for M. stellatus because regeneration from holdfasts is slower than in C. crispus. A reduced surface area:biomass ratio coupled with greater strength may lessen wave-induced disturbance and be important to maintaining a high abundance of M. stellatus in the low intertidal zone of wave-swept shores.
The alpha-diversity (number of species in a small, homogeneous area) data of intertidal seaweeds sampled in the lower eulittoral zone at 18 sites along the Namibian coast was statistically analysed to study the effect of wave exposure, sand inundation, limpets and mussels. Seaweed diversity was found to be controlled by a number of interacting factors. Diversity was strongly related to the degree of sand inundation where sand exceeded 5.6 kg m-2. In areas where sand was below 5.6 kg m-2, mussel biomass seemed to be the most important factor affecting seaweed diversity and sand had little or no affect; mussel biomass negatively affected seaweed diversity, but was positively correlated with the degree of wave exposure. Thus an increase in wave exposure indirectly led to a decrease in seaweed species diversity. The degree of wave action was however positively correlated with seaweed diversity in quadrats where mussels were absent. Limpets had no apparent effect on seaweed diversity or richness, probably due to their low biomass value.
Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m−2 day−1, wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m−2 day−1) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre−1 for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre−1 for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g−1 for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m−3 as Chl. a, sharply increased up to 100 mg m−3 only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).
Simple Monte Carlo significance testing has many applications, particularly in the preliminary analysis of spatial data. The method requires the value of the test statistic to be ranked among a random sample of values generated according to the null hypothesis. However, there are situations in which a sample of values can only be conveniently generated using a Markov Chain, initiated by the observed data, so that independence is violated. This paper describes two methods that overcome the problem of dependence and allow exact tests to be carried out. The methods are applied to the Rasch model, to the finite lattice Ising model and to the testing of association between spatial processes.
Power is discussed in a simple case.
Saccorhiza polyschides (Lightf.) Batt. is a laminarian alga found in the sublittoral region. It is widely distributed around the shores of the British Isles and is particularly common on the south west coast of Ireland. A puzzling aspect of the distribution of the species in Southern Ireland is its absence from Lough Ine, in County Cork.
The sublittoral benthic vegetation of the eastern Basque coast was studied along 55 km of coast. Information concerning the abundance of macrophytes and the physical environmental characteristics (type and slope of substratum, level of sedimentation, sediment nature and depth) was obtained in a network of 376 quadrats. The predominance of a habitat type (slightly sloping regular bedrock, little-moderate sand sedimentation levels and a depth range of 4-9 m) involves the development of a very homogeneous vegetation constituted mainly of Gelidium sesquipedale beds. Sedimentation, probably in relation to wave exposure, was the environmental factor showing the widest range of variation, and appeared to determine to the vegetation gradient detected by the correspondence analysis which shows algal distribution as a continuum. Along an increasing sedimentation gradient, the following trends have been detected: (1) Algal cover decrease due to the vertical layering reduction. (2) Changes in the relative abundance among species: Gelidium sesquipedale and Mesophyllum lichenoides were negatively associated with sediment; Pterosiphonia complanata and Cystoseira baccata were well adapted to sedimentation, showing an optimum development at moderate to high levels; Halopithys incurvus and Chondracanthus acicularis achieved their optimum development at high to very high sedimentation levels in shallow waters. (3) Vegetation heterogeneity, diversity and epiphytism increase. In addition, pollution, causing an increase of allochthonous sediments and turbidity, was the other environmental factor affecting the structure and composition of the vegetation. This fact was reflected by the presence of a residual Gelidium sesquipedale vegetation smothered by silt close to an urban effluent, and a vegetation of Cladostephus spongiosus - Chondria coerulescens - Pterosiphonia pennata in the vicinity of several ports. Multivariate analyses have proven to be a useful tool to detect marine vegetation structure, showing that in the study area discrete communities are not distinguishable.
The intertidal vegetation of the 'Abra de Bilbao' (Basque coast, N Spain) was studied following a pollution gradient. Under the effect of pollution, several signs of alteration are detected in the vegetation, which responds by simplifying its structure. Species which require high quality environmental characteristics such as Cytoseira tamariscifolia, Cystoseira baccata, Bifurcaria bifurcata, Gelidium sesquipedale, Gigartina pistillata and Laurencia obtusa disappear, whereas Corallina elongata, Chondria coerulescens, Caulacanthus ustulatus and Gelidium pusillium become dominant in successive steps as pollution increases. In general, large perennial algae are replaced by small turfing algae. In addition, an intensification of the herbivorous activity (mainly limpets) occurs on the soft caespitose vegetation. Species richness and algal abundance suffer a reduction. In the most degraded environmental conditions, vegetation is replaced by filter-feeders (mussels and barnacles), and cyanobacteria proliferate. Pollution also alters the zonation pattern reducing in the number of vegetation belts.
During the last two decades conditions in the polluted shelf area of the Northern Adriatic became critical, leading to eutrophication and anoxia. They are reflected in changes and degradation of the macrophytobenthos with simultaneous increase of phytoplankton blooms. Pollution-induced changes of the benthic algal vegetation comprise altered zonation patterns and leading algal associations along with a decrease in species number and fresh weight biomass. A reduction or absence of fucoid stands was observed in the eulittoral and sublittoral. Fucus virsoides was in most cases replaced by ephemeral species which form distinct zones during spring and by turf-like mats of Gelidium pusillum.
Sublittoral Cystoseira stands were either reduced or absent, replaced by populations of Halopteris scoparta, Dictyota dichotoma, Halopithys incurvus, Padina pavonica and under extreme conditions by Ulva rigida with Scytosiphon lomentaria and Enteromorpha species during spring. A decreased depth penetration of macroalgae was observed in polluted sites. It seems likely that amorphous mucus aggregations resulting probably from excess phytoplankton blooms which were found during summer months of the last few years, have a deleterious effect on macroalgae.
Rocky ocean bottoms are covered from time to time with small amounts of fine sediments. This material may interfere with the development of germling stages of Macrocystis pyrifera. Tests were performed by introducing sediments before and after spores were dispersed in culture dishes. 10 mg cm-2 of sediment, enough to occlude the surface, prevents spore attachment, greatly reducing the probability of survival. Smothering of established germlings was severe at 108 mg sediment cm-2. Water motion further reduced spore success where sediments were present, probably because of abrasive scour. Mechanisms of natural and human interference with M. pyrifera reproduction are suggested.
The uptake of inorganic carbon into the thallus of Macrocystis pyrifera (L.) C. Ag. requires first that the inorganic carbon pass through the water medium to the plant surface. This transfer of inorganic carbon to the thallus must take place through a boundary layer. Experiments in water tunnels indicate that the boundary layer adjacent to the M. pyrifera blade may be turbulent in water speeds as low as 1 cm sec-1. Photosynthetic output of the blade can be increased by a factor of 300% by increasing water speeds over the blade surface from 0 to 4 cm sec-1. This is consistent with a decrease in the thickness of the boundary layer. Above 4 cm sec-1, the assimilation of carbon was limiting. The assimilation of carbon is generally known to follow Michaelis-Menten-like kinetics. Combining the two uptake steps into an overall model of carbon uptake agrees well with photosynthetic data obtained from M. pyrifera under varying conditions of water speed and bicarbonate concentrations in the laboratory. The ecological and morphological consequences of these findings are discussed.
Algal succession within a subtidal forest of the giant kelp Macrocystis pyrifera was studied by following colonization and community development on concrete blocks fastened to the bottom. Sets of blocks were placed in the bed at 3-month intervals. Subsequent algal development on each set was followed for over a year. All macroscopic species attached to the substrata were noted, and the number and lenght of basal branches determined every 1 to 3 months. Colonizing plants fell into 3 categories: rapid-growing ephemerals, and rapid and slow-growing perennials. Ephemerals such as Giffordia (Ectocarpus) mitchellae, Colpomenia peregrina, and diatom films generally produced and initial bloom on the blocks but were gradually replaced by perennials (articulated corallines, Rhodymenia spp., Gigartina spp.) characteristic of the mature kelp community. These stages, rather than representing ecological succession, seemed to reflect differences in growth rate and success in interspecific competition for space and light. Colonization on the blocks varied with season, indicating that most species have either a spring-summer or fall-winter period of maximum reproduction. M. pyrifera sporophyte colonization was greatest in spring. During community development, algal diversity (H), number of species (s) and evenness (J) all reached a peak within 100 to 200 days regardless of the time the blocks were started. Diversity and number of species then fell as ephemeral species disappeared. These species were apparently unable to compete with perennials and, once gone, did not recolonize. Evenness remained high.
Detrended correspondence analysis (DCA) is an improvement upon the reciprocal averaging (RA) ordination technique. RA has two main faults: the second axis is often an arch or horseshoe distortion of the first axis, and distances in the ordination space do not have a consistent meaning in terms of compositional change (in particular, distances at the ends of the first RA axis are compressed relative to the middle). DCA corrects these two faults. Tests with simulated and field data show DCA superior to RA and to nonmetric multidimensional sealing in giving clear, interpretable results. DCA has several advantages. (a) Its performance is the best of the ordination techniques tested, and both species and sample ordinations are produced simultaneously. (b) The axes are scaled in standard deviation units with a definite meaning, (c) As implemented in a FORTRAN program called DECORANA, computing time rises only linearly with the amount of data analyzed, and only positive entries in the data matrix are stored in memory, so very large data sets present no difficulty. However, DCA has limitations, making it best to remove extreme outliers and discontinuities prior to analysis. DCA consistently gives the most interpretable ordination results, but as always the interpretation of results remains a matter of ecological insight and is improved by field experience and by integration of supplementary environmental data for the vegetation sample sites.
A seasonal study of sand movement and the benthic intertidal organisms at Bound Rock, New Hampshire, USA was conducted between November, 1973 and February, 1975. The site is subjected to irregular sand fluctuations, as well as diurnal, neapspring and major summer sand intrusions. The abundance and distribution of intertidal species was interrelated with the historical sand fluctuations at the area. For example, the lower limits of Mytilus edulis, Balanus balanoides and Porphyra umbilicalis approximated the highest summer sand elevations. Highly abraded rock surfaces in the lower intertidal zone were dominated by opportunistic annuals (e.g. Enteromorpha spp.) and perennial psammophytic or sand-loving seaweeds (e.g. Ahnfeltia plicata and Sphacelaria radicans). Overall, the intertidal seaweed populations at Bound Rock showed a lower number of perennials and fewer species than adjacent rocky shores. The low species diversity of seaweeds at the study site is attributable to unstable environmental conditions and a limited number of habitats. Even so, several psammophytic microhabitats are evident at Bound Rock depending upon the extent of sand burial and abrasion. The morphological and reproductive adaptations of several psammophytic species are discussed.
Available data on determinants of production in species of Gelidium suggest several general patterns. Species diversity is higher in tropical latitudes, whereas in temperate latitudes the size of the fronds is larger, the species are ecologically dominant and commercially viable. Typically, the species occur on rocky substrate, often on coralline crusts, associated with rapid water movement and arranged in successive belts that can extend down to 25 m depth. Yields vary among species, to a maximum of 2.0 kg m–2 y–1. Growth and production in many species can best be explained by complex interactions between irradiance and nutrients. Temperature can interact synergistically with irradiance, while water movement compensates for nutrient limitations. Increased water movement or the addition of nutrients can prevent, to an extent, bleaching by high light and high temperature. Available data suggest the existence of at least eight biological factors affecting predicted productivity of Gelidium crops: morphology, age of the frond, thallus part, reproductive state, seasonality, crop density, life history phase and geographic and ecological origin of the species. At least four events can remove or destroy Gelidium crops: extreme low tides, storms, grazing and careless harvesting. Only the last-named factor has been analyzed over more extensive experimental periods.
The biological effects of a low-volume domestic sewage discharge were studied near Wilson Cove, San Clemente Island, California (USA), from February to June, 1972. There were fewer species and less cover near the outfall (7 macro-invertebrates, 17.6%; 13 macrophytes, 91.7%) than in nearby unpolluted control areas (9 macroinvertebrates, 9.2%; 30 macrophytes, 103.4%). The outfall biota was less diverse than that of the controls, as shown by 5 different diversity indices. A great reduction in community stratification (spatial heterogeneity) and, hence, community complexity occurred near the outfall; this reduction in stratification was primarilly due to the absence of Egregia laevigata, Halidrys dioica, Sargassum agardhianum and Phyllospadix torreyi. These were replaced in the mid-intertidal near the outfall by a low turf of blue-green algae, Ulva californica, Gelidium pusillum and small Pterocladia capillacea, and in the lower intertidal by Serpulorbis squamigerus covered with Corallina officinalis Var. chilensis. A statistically-based determination of assemblages or groups of organisms (i.e., cluster analysis) revealed 3 discrete outfall and 3 discrete control area groups; 3 assemblages contained samples from both areas. The distributional patterns of these groups indicate that near the outfall the degree of dilution of discharged sewage is more important in regulating zonation than is tidal height. The enhancement of the suspension feeder Serpulorbis squamigerus and the omnivores Ligia occidentalis, Pachygrapsus crassipes and Anthopleura elegantissima in the outer fringe of the outfall plume hypothetically is due to their ability to utilize sewage as a food source. A critical effect of the outfall may be to decrease environmental stability thereby favoring rapid-colonizers and more sewage-tolerant organisms. The outfall macrophytes were characterized by relatively higher net primary productivities, smaller growth forms, simpler and shorter life histories, and most were components of early successional stages.
From a series of 10 quarterly assessment between October 1975 and May 1978 (inclusive), fluctuations in abundance were determined for macroinvertebrates and macrophytes of a rocky intertidal community on Santa Cruz Island, California, USA. During afternoon low tides in late fall and winter of the first 2 yr of study, organisms of the upper and middle intertidal zones were subjected to prolonged aerial exposure. Many species there tolerated this exposure, but die-backs occurred for a barnacle (Chthamalus fissus/C. dalli) and several algae (Endocladia muricata, Pelvetia fastigiata f. gracilis, Corallina officinalis var. chilensis, Corallina vancouveriensis, Cylindrocarpus rugosus and Codium fragile). These die-backs were succeeded by blooms of Ulva californica and Porphyra perforata. In the upper and middle intertidal zones, the major cover organisms that could tolerate prolonged aerial exposure were disproportionately prevalent and appeared to be maintained by the periodic repression of species intolerant to such exposure. In February 1978, heavy rainfall caused sediment inundation of the middle and lower intertidal zones. This event was followed by declines in abundance of a barnacle (Tetraclita rubescens) and several algae (Pelvetia fastigiata f. gracilis and corallina spp.). Shannon-Wiener H species diversity fluctuated from a high in October to a low the following May during both 1975–1976 and 1976–1977 in conjunction with the period of increased daytime aerial exposure in late fall and winter. A further decline in diversity following sediment inundation in February 1978 contributed to a long-term trend of declining H species diversity (3.06 in October 1975 to 1.87 in May 1978). We hypothesize that predictable late fall to winter aerial exposure stresses, in combination with a random physical disturbance (sediment burial), exceeded an optimal intermediate level of disturbance predicted for maximal species diversity.
Sand covers the substratum in a layer that varies in depth throughout the year, forming a structural component in mats of small algal thalli on flat rocky beaches in southern California. The summer maximum and winter minimum in quantity of sand coincide with periods of relatively calm and relatively stormy weather, respectively. Many of the abundant non-perennial algal species in the turf attach only to other thalli and to sand grains; several exhibit a creeping growth habit over the surface of the sand. It is suggested that seasonal variations in relative abundance of algal species and the persistence of the several perennial species of algae that dominate the vegetation are consequences of adaptations to the presence and movement of sediment in the habitat.