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Typical understorey algae at different depths in the sublittoral zone off Helgoland (from Lüning, 1970; 1990).
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... understorey flora of kelp beds varies with depth and geographical location and may be depauperate (as in silted habitats) or very rich. The zonation patterns of the understorey algae are related to the available light rather than to the physical depth. Some indication of the complexity of the community is illustrated by Fig. 3, where the kelp forest peters out at a depth of about 7 m. and the lowest depth of algal growth is 15 m. due to the turbidity of the local water conditions. With few exceptions, algal surveys have been confined to the summer months and, although this is generally a good season for recording algae, there is the drawback that species ...
Context 2
... the zonation diagram of the understorey algae of kelp forests in Helgoland (Fig. 3), Lüning (1970; 1990) illustrates more than 20 species of algae that are commonly found, excluding the kelp species themselves and the several species of encrusting algae. The species present in the understorey of UK kelp beds vary tremendously with depth within a site (if the algae are on the kelp stipes) and within a particular kelp ...
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... Free-living coralline algae, depending on the size, inner structure, external shape, algal growth forms, and taxonomic composition, are characterized by three different morphotypes: boxwork (usually large and vacuolar), praline (compact and nodular) and branches [15][16][17]. The main environmental factors controlling the development of coralline algae beds are light, temperature, nutrients, hydrodynamism (i.e., waves and currents), and bioturbation phenomena that avoid the coralline algae being buried by sediments [18][19][20][21][22]. Rhodolith/maerl beds may be considered as a non-renewable resource [7,16] and are in need of important protection and conservation actions. ...
Coralline algal beds are comprised of biogenic calcareous formations considered a habitat of high conservation interest, hosting a high great biodiversity. To assess the status of this habitat in the Italian seas, we report results from a systematic analysis of the available scientific literature. Italian rhodolith/maerl beds are reported on 31 Italian sites mostly located around islands, shoals, banks, terraces, and gentley sloping shelves, from 9 m to 130 m water depth (with a mean depth of about 56 m). The dominant species occurring in the Italian submarine sites are Phymatolithon calcareum and Lithothamnion corallioides, with a rich associated fauna including sponges, bryozoans, hydrozoans, polichaetes, molluscs, amphipods, gastropods, echinoderms. Despite the high biodiversity characterizing the Italian rhodolith/maerl beds, only seven submarine sites hosting this sensitive habitat are part of Marine Protected Areas (MPAs). This evidence highlights the need for actions focused on the implementation of effective management and proper conservation measures to preserve such precious habitats. Protection of this habitat cannot be effectively provided without access to multidisciplinary data (e.g., geospatial, biological, geophysical, geomorphological data) capable of assessing its spatial distribution and biological characteristics over wide areas. An increased research effort to improve the production of fine-scale distribution maps and monitoring activities is therefore needed.
... Although rhodoliths and maërl are quite similar in semantic terminology [21][22][23], rhodoliths include dead and alive unattached coralline red algae, whereas maërl only represents living, branched coralline thalli [24,25]. When its palaeoecological relevance was recognized, the word "rhodolith" was coined to describe a particular form of red stone [14,26]. ...
... The rhodoliths' morphology and phytal composition (i.e., related fauna in algae) and, consequently, the heterogeneity of rhodolith beds, are strongly influenced by hydrodynamism and light [76]. Rhodoliths are usually more common in zones with moderate to high-energy currents (excluding the L. corallioides and P. calcareum mentioned above) [21,77]. However, they may exhibit significant morphological polymorphism, which is associated with hydrodynamism: the size, shape and the pattern of the ramification of the rhodoliths are mostly influenced by local hydrodynamics [7,36]. ...
... However, they may exhibit significant morphological polymorphism, which is associated with hydrodynamism: the size, shape and the pattern of the ramification of the rhodoliths are mostly influenced by local hydrodynamics [7,36]. The species composition of rhodolith beds, on the other hand, is also influenced by light penetration and depth, sedimentation, the temperature of the water, salinity and water quality [21], among other factors. This complexity of conditions commonly causes sporadic and irregular distribution patterns of rhodoliths on the ocean floor [36], where the rhodolith beds intercalate with sandy bottoms, forming mosaics within marine environments [78]. ...
Red calcareous algae create bio-aggregations ecosystems constituted by carbonate calcium, with two main morphotypes: geniculate and non-geniculate structures (rhodoliths may form bio-encrustations on hard substrata or unattached nodules). This study presents a bibliographic review of the order Corallinales (specifically, rhodoliths), highlighting on morphology, ecology, diversity, related organisms, major anthropogenic influences on climate change and current conservation initiatives. These habitats are often widespread geographically and bathymetrically, occurring in the photic zone from the intertidal area to depths of 270 m. Due to its diverse morphology, this group offers a special biogenic environment that is favourable to epiphyte algae and a number of marine invertebrates. They also include holobiont microbiota made up of tiny eukaryotes, bacteria and viruses. The morphology of red calcareous algae and outside environmental conditions are thought to be the key forces regulating faunistic communities in algae reefs. The impacts of climate change, particularly those related to acidification, might substantially jeopardise the survival of the Corallinales. Despite the significance of these ecosystems, there are a number of anthropogenic stresses on them. Since there have been few attempts to conserve them, programs aimed at their conservation and management need to closely monitor their habitats, research the communities they are linked with and assess the effects they have on the environment.
... The Breton term "maërl," originally used to describe both living and dead algal gravels, refers to free calcareous nodules of unattached coralline ( Fig. 6.4A and B) that can be found in across the Atlantic and Pacific Oceans to the Arctic (Ballesteros, 2006;Barberá et al., 2003;Riosmena-Rodríguez, Nelson, & Aguirre, 2017), and are usually constrained to shallow waters and bay environments (Birkett, Maggs, & Dring, 1998;Riosmena-Rodríguez et al., 2017). Nevertheless, on insular areas with low fluvial discharge and lower light attenuation values, maërl beds can develop at deeper depths (Birkett et al., 1998;Canals & Ballesteros, 1997;Jacquotte, 1962) down to the limit of the continental shelf (Ballesteros, 1994;Santín et al., 2018). ...
... The Breton term "maërl," originally used to describe both living and dead algal gravels, refers to free calcareous nodules of unattached coralline ( Fig. 6.4A and B) that can be found in across the Atlantic and Pacific Oceans to the Arctic (Ballesteros, 2006;Barberá et al., 2003;Riosmena-Rodríguez, Nelson, & Aguirre, 2017), and are usually constrained to shallow waters and bay environments (Birkett, Maggs, & Dring, 1998;Riosmena-Rodríguez et al., 2017). Nevertheless, on insular areas with low fluvial discharge and lower light attenuation values, maërl beds can develop at deeper depths (Birkett et al., 1998;Canals & Ballesteros, 1997;Jacquotte, 1962) down to the limit of the continental shelf (Ballesteros, 1994;Santín et al., 2018). While not abundant or relatively localized, maërl beds are considered as one of the most productive habitats of the temperate regions (Martin et al., 2005;Martin, Clavier, Chauvaud, & Thouzeau, 2007a), and have a paramount role in the production of carbonate (Bosence & Wilson, 2003;Martin, Clavier, Chauvaud, & Thouzeau, 2007b) and pH regulation (Canals & Ballesteros, 1997), which also prompts their harvesting for industrial uses (Mac Monagail, Cornish, Morrison, Araújo, & Critchley, 2017). ...
... Maërl beds may also be important nursery areas for commercially valuable mollusks and crustaceans. This aspect has not been well studied, but there is good evidence that they are nurseries for at least a few species such as the black sea urchin Paracentrotus lividus (Lamarck, 1816) in maërl deposits in Ireland and scallops on maërl beds in France and west Scotland (Birkett et al., 1998;Keegan, 1974). They also provide structurally complex feeding areas for juvenile fish such as the Atlantic cod and reserves of commercial brood stock for species such as Pecten maximus (Linnaeus, 1758), Venus verrucosa (Linnaeus, 1758), and Ensis spp. ...
n this chapter, we will mainly focus on some of the most relevant low-light habitats among those found along the
continental shelf and margins, including habitats which receive multiple human-induced disturbances, unique and
scarcely known assemblages (e.g., brachiopod beds), as well as those for which we have relatively better ecological
knowledge (e.g., marine caves, coralligenous outcrops and maërl beds, cold water corals, among others). These hab-
itats are characterized by a wide variety of faunistic compositions and traits. Nevertheless, all of them have in com-
mon their low-light conditions and are difficult for humans to access, therefore being almost unexplored until recent
times. We will highlight how modern sampling techniques have improved our understanding of such habitats, their
main characteristics and ecological relevance, major threats and the efficiency of the management, conservation, and
restoration strategies (if any) carried out to date.
... The Breton term "maërl," originally used to describe both living and dead algal gravels, refers to free calcareous nodules of unattached coralline ( Fig. 6.4A and B) that can be found in across the Atlantic and Pacific Oceans to the Arctic (Ballesteros, 2006;Barberá et al., 2003;Riosmena-Rodríguez, Nelson, & Aguirre, 2017), and are usually constrained to shallow waters and bay environments (Birkett, Maggs, & Dring, 1998;Riosmena-Rodríguez et al., 2017). Nevertheless, on insular areas with low fluvial discharge and lower light attenuation values, maërl beds can develop at deeper depths (Birkett et al., 1998;Canals & Ballesteros, 1997;Jacquotte, 1962) down to the limit of the continental shelf (Ballesteros, 1994;Santín et al., 2018). ...
... The Breton term "maërl," originally used to describe both living and dead algal gravels, refers to free calcareous nodules of unattached coralline ( Fig. 6.4A and B) that can be found in across the Atlantic and Pacific Oceans to the Arctic (Ballesteros, 2006;Barberá et al., 2003;Riosmena-Rodríguez, Nelson, & Aguirre, 2017), and are usually constrained to shallow waters and bay environments (Birkett, Maggs, & Dring, 1998;Riosmena-Rodríguez et al., 2017). Nevertheless, on insular areas with low fluvial discharge and lower light attenuation values, maërl beds can develop at deeper depths (Birkett et al., 1998;Canals & Ballesteros, 1997;Jacquotte, 1962) down to the limit of the continental shelf (Ballesteros, 1994;Santín et al., 2018). While not abundant or relatively localized, maërl beds are considered as one of the most productive habitats of the temperate regions (Martin et al., 2005;Martin, Clavier, Chauvaud, & Thouzeau, 2007a), and have a paramount role in the production of carbonate (Bosence & Wilson, 2003;Martin, Clavier, Chauvaud, & Thouzeau, 2007b) and pH regulation (Canals & Ballesteros, 1997), which also prompts their harvesting for industrial uses (Mac Monagail, Cornish, Morrison, Araújo, & Critchley, 2017). ...
... Maërl beds may also be important nursery areas for commercially valuable mollusks and crustaceans. This aspect has not been well studied, but there is good evidence that they are nurseries for at least a few species such as the black sea urchin Paracentrotus lividus (Lamarck, 1816) in maërl deposits in Ireland and scallops on maërl beds in France and west Scotland (Birkett et al., 1998;Keegan, 1974). They also provide structurally complex feeding areas for juvenile fish such as the Atlantic cod and reserves of commercial brood stock for species such as Pecten maximus (Linnaeus, 1758), Venus verrucosa (Linnaeus, 1758), and Ensis spp. ...
n this chapter, we will mainly focus on some of the most relevant low-light habitats among those found along the
continental shelf and margins, including habitats which receive multiple human-induced disturbances, unique and
scarcely known assemblages (e.g., brachiopod beds), as well as those for which we have relatively better ecological
knowledge (e.g., marine caves, coralligenous outcrops and maërl beds, cold water corals, among others). These hab-
itats are characterized by a wide variety of faunistic compositions and traits. Nevertheless, all of them have in com-
mon their low-light conditions and are difficult for humans to access, therefore being almost unexplored until recent
times. We will highlight how modern sampling techniques have improved our understanding of such habitats, their
main characteristics and ecological relevance, major threats and the efficiency of the management, conservation, and
restoration strategies (if any) carried out to date.
... This favours an increase in both the biodiversity and the functional diversity of these assemblages (see a review in Nelson 2009). In addition, the three-dimensional frameworks created within these detritic bottoms protect organisms against predation (Teichert et al. 2014), favour their reproduction (Teichert et al. 2014), and serve as nursery grounds for many species (Basso et al. 2017;Birkett et al. 1998;Kamenos et al. 2004aKamenos et al. , 2004bKamenos et al. , 2004c, a number of those organisms being of commercial interest Ordines et al. 2015;Steller et al. 2003). ...
... The development of maërl beds is linked to the interactive and/or synergistic influence of several environmental factors, especially light, temperature and sedimentation (Adams et al. 2020;Pérès andPicard 1955, 1964;Wilson et al. 2004), their depth limit primarily dependent on the degree of light penetration (Barberá et al. 2003;Wilson et al. 2004). Consequently, such beds have been observed at depths of 290 m in the clear waters of the Bahamas (Littler et al. 1991), to 30 m in the more turbid waters of the Northeast Atlantic (Birkett et al. 1998), between 25 and 120 m in the Western Mediterranean Birkett et al. 1998;Giaccone et al. 1994), and to 180 m in the Eastern Mediterranean basin (Basso 1996). In addition, water movement (Adams et al. 2020;Foster 2001;Steneck 1986) and bioturbation (Marrack 1999) must be sufficient to keep the periodic rotations necessary to provide light to all surfaces of the thalli. ...
... The development of maërl beds is linked to the interactive and/or synergistic influence of several environmental factors, especially light, temperature and sedimentation (Adams et al. 2020;Pérès andPicard 1955, 1964;Wilson et al. 2004), their depth limit primarily dependent on the degree of light penetration (Barberá et al. 2003;Wilson et al. 2004). Consequently, such beds have been observed at depths of 290 m in the clear waters of the Bahamas (Littler et al. 1991), to 30 m in the more turbid waters of the Northeast Atlantic (Birkett et al. 1998), between 25 and 120 m in the Western Mediterranean Birkett et al. 1998;Giaccone et al. 1994), and to 180 m in the Eastern Mediterranean basin (Basso 1996). In addition, water movement (Adams et al. 2020;Foster 2001;Steneck 1986) and bioturbation (Marrack 1999) must be sufficient to keep the periodic rotations necessary to provide light to all surfaces of the thalli. ...
This bionomic study of the detritic bottoms dominated by macroalgae from the south of Mallorca (Balearic Islands, Western Mediterranean) includes a quantitative description of the algal communities found in the area, as well as their bathymetric and geographical distribution. The results presented here are based on data collected in two oceanographic campaigns conducted in July 2012 and September 2014, using a Jennings beam trawl. A hierarchical group average agglomerative clustering, accompanied by the SIMPROF test, allowed the identification of seven different macroalgal communities, of which two are described here for the first time: the Cryptonemia longiarticulata fields and the Maërl beds of indeterminate rhodoliths. Depth and rhodolith abundance were the two main features driving the distribution of these communities. We found that seven species contributed 70% of the similarity between samples (SIMPER test), with the indeterminate species of rhodoliths (23.6%) and the encrusting fleshy red alga, Agissea inamoena (15.6%) being the most important. The methodology used for the sample selection and quantification processes turned out to be very efficient and faster than other methods used for the characterization of macroalgal communities from detritic bottoms, suggesting that this study could serve as a baseline for similar studies and for future management and conservation actions.
... Growth rates are highest in April and May, slowing in June and July as the blades become damaged (Birkett et al., 1998;Tyler-Walters, 2008). ...
While seaweed aquaculture is generally promising from industry and ecological perspectives, most companies fail to become entirely profitable. This study aims to compare the impact of using two partial harvests to a single harvest on seaweed yield, biofouling, chemical composition, cost, and consumer preferences for Alaria esculenta farmed in the Faroe Islands. The study also aims to help identify ideal, cost-efficient harvesting methodologies that ensure the financial and ecological success of the industry. During the study, 50-meter-long lines were either trimmed in harvest 1 (June 2021) and entirely harvested in harvest 2 (August 2021, partial harvest), entirely harvested in harvest 1 (total harvest), or left unharvested during harvest 1 and 2 (control). Yield, biofouling, chemical composition, and economic analyses were compared between each trial.
Partial harvests did not significantly impact the harvest wet weight compared to a total harvest, and blade length decreased from harvest 1 (70-80 cm) to harvest 2 (46-57 cm). Biofouling cover in harvest 1 (1-4% cover) was signficantly lower than harvest 2 (7-8% cover) and showed a succession of epibionts from filamentous algae in harvest 1 to bryozoan in harvest 2. Biofouling likely reduced the growth of harvest 2 lines. Harvest 2 biomass was too fouled to be sold as human food, and harvest 1 had 3.5 times higher concentrations of bioactivity measurements (TPC) compared to harvest 2. However, all concentrations of potentially harmful elements peaked in harvest 1, potentially representing the bioabsorptive properties of A. esculenta without epibionts. Economically, average cost per kg (dry weight) seaweed was 1.4-1.7 times lower in the total harvest compared to the partial harvest. These results indicate that partially harvesting seaweed is not an effective method to increase yield and quality or reduce costs.
Developing good farming methods is essential for the environmental sustainability of seaweed farming. This study also indicates that harvest timing is more impactful than partially harvesting. Future studies should focus on analyzing yield, quality, and costs over time to optimize the harvesting time for specific locations.
... Rhodoliths are unattached nodules formed mostly by CCA. Among them, free-living unattached branches usually characterize maerl beds in the northeastern Atlantic Ocean (Henrich et al., 1995;Birkett et al., 1998;Bárbara, 2008, 2009;Peña et al., 2014) and in the Mediterranean Sea (Huvé, 1956;Jacquotte, 1962;Gambi et al., 2009;Agnesi et al., 2011;Savini et al., 2012;Basso et al., 2017). ...
Recent advances on the mechanism and pattern of calcification in coralline algae led to contradictory conclusions. The evidence of a biologically controlled calcification process, resulting in distinctive patterns at the scale of family, was observed. However, the coralline calcification process has been also interpreted as biologically induced because of the dependency of its elemental composition on environmental variables. To clarify the matter, five collections of Lithothamnion corallioides from the Atlantic Ocean and the Mediterranean Sea, across a wide depth range (12–66 m), have been analyzed for morphology, anatomy and cell wall crystal patterns in both perithallial and epithallial cells to detect possible ultrastructural changes. L. corallioides shows the alternation of tiers of short-squared and long-ovoid/rectangular cells along the perithallus, forming a typical banding. The perithallial cell length decreases according to water depth and growth rate, whereas the diameter remains constant. Our observations confirm that both epithallial and perithallial cells show primary (PW) and secondary (SW) calcite walls. Rectangular tiles, with the long axis parallel to the cell membrane forming a multi-layered structure, characterize the PW. Flattened squared bricks characterize the SW, with roundish outlines enveloping the cell and showing a zigzag and cross orientation. Long and short cells have different thicknesses of PW and SW, increasing in short cells. Epithallial cells are one to three flared cells with the same shape of the PW and SW crystals. Despite the diverse seafloor environments and the variable L. corallioides growth rate, the cell walls maintain a consistent ultrastructural pattern with unaffected crystal shape and arrangement. A comparison with two congeneric species, L. minervae and L. valens, showed similar ultrastructural patterns in the SW but evident differences in the PW crystal shape. Our observations point to a biologically control rather than an induction of the calcification process in coralline algae and suggest a possible new morphological diagnostic tool for species identification, with relevant importance for paleontological applications. Finally, secondary calcite, in the form of dogtooth crystals that fill the cell lumen, has been observed. It represents a form of early alteration in living collections which can have implications in the reliability of climate and paleoclimate studies based on geochemical techniques.
... The predominance of spheroidal shapes is linked to strong transport or frequent turning (Ávila and Riosmena-Rodriguez, 2011;Sneed and Folk, 1958) that modulates the rhodolith shape as it grows (Foster, 2001;Steller and Foster, 1995). However, rhodolith shape and species composition also can change on a spatial scale, subdue to environmental variables such as current's strength, wave action, wind effect, depth and sediment beneath (Birkett et al., 1998;Bosence, 1979;Foster, 2001;Steller and Foster, 1995;Tâmega et al., 2014). Spheroidal rhodoliths are quite common mainly at shallow waters Gherardi, 2004;Minnery, 1990), including in fossil record (Johnson et al., 2011), due to their high oceanic motion (Marrack, 1999), a common feature on Brazilian beaches (Amado-Filho et al., 2007;Bahia et al., 2010;Pascelli et al., 2013;Short and Klein, 2016). ...
This study characterized rhodolith beds and the structure and function of their invertebrate communities in three tropical beaches subjected to different environmental impacts. The highest rhodolith density and invertebrate diversity and density were found on a beach with coarser sands (interpreted as indicative of higher hydrodynamics) and the high availability of calcium carbonate in nearby locations. On the opposite, higher rhodolith mortality, lower invertebrate diversity and density were recorded in the beach with high thermotolerant coliforms concentrations and finer sands. The functional composition was similar in the less polluted beaches, despite differences in sediment composition. In these beaches, polychaetes and echinoderms dominated, being primarily biodiffusors, with slow free movement and predators. These traits appeared advantageous due to food and structural protection provided by rhodoliths while providing oxygenation and remobilization of sediment by resident biodiffusers fauna. The most polluted beach was marked by lower densities of those taxa and traits, with suspension feeders’ bivalve dominance, with limited movement, associated with higher suspended material, common in organic polluted environments.
... In this study we assess the mobility of rhodoliths, defined as nodular calcareous aggregates composed mainly of nongeniculate coralline red algae (Foster, 2002), which usually occur in mobile biogenic sediment deposits, although the coalescence of nodules flagging wide areas, forming rhodolith beds, has been also reported (Francini-Filho et al., 2018;Moura et al., 2021). The heterogeneous spatial distribution of rhodoliths is a consequence of their sensitivity to light intensity, currents, wave action, sedimentation rates, and salinity, whereas mesophotic, low sedimentation quiescent conditions are optimal (Birkett et al., 1998). Rhodoliths are found in relatively shallow waters but can also occur at greater depths (e.g., Littler et al., 1991;Moura et al., 2016;Francini-Filho et al., 2018). ...
Rhodolith beds can contribute large amounts of CaCO3 to coastal environments, playing an important role in Carbon sequestration. The spatial distribution of rhodoliths is a consequence of their sensitivity to light intensity, currents, wave action, sedimentation rates, and salinity, whereas mesophotic, low sedimentation quiescent conditions are optimal. Although there is evidence of a clear relationship between hydrodynamics and rhodolith morphology and mobility, there are few studies relating wave action and rhodolith mobility. We aim to assess the mobility potential by waves, of the rhodoliths of the Abrolhos Shelf (Brazil), that contains the largest rhodolith field in the world. Based on the local wave climate and its propagation through the shelf, the rhodolith mobility potential was evaluated. Rhodolith mobility potential distribution is directly related to shelf morphology and incoming waves characteristics. Despite being restricted to deeper areas of the shelf (>20 m), rhodoliths in the area are mobilized by wave action, especially from the more energetic waves associated with storms. Waves can mobilize rhodoliths in the area, with mobility potential distribution being controlled by shelf morphology and seasonal wave climate. Largest areas of mobilization are observed during energetic waves conditions associated to the passage of cold fronts.
... Key index words: calcification; coralline algae; environmental conditions; field experiment; photosynthesis; physiology; plasticity; rhodoliths Abbreviations: Ω Ar , aragonite saturation state; CTD probe, conductivity temperature and depth probe; DIC, dissolved inorganic carbon; E, irradiance; Ec, irradiance of compensation; Ek, irradiance of saturation; G, net calcification; G D , calcification in the dark; G MAX , maximal gross calcification; G L , calcification in the light; GPP, gross primary production; GPP MAX , maximal gross primary production; KW, Kruskal-Wallis test; MPT, Monte Carlo permutation test; NPP, net primary production; pH T , total scale pH; R, respiration; R/V, research vessel; Si(OH) 4 , silicate; T A , total alkalinity; v/v, volume (solute) per volume (solvent); Y MAX , maximal gross yield Free-living nongeniculate coralline algae, also referred as maerl (or rhodoliths), are distributed worldwide in coastal systems stretching from the tropics to polar regions (Foster 2001). They can accumulate and form large beds of live and/or dead maerl (Birkett et al. 1998). Individual thalli can range from 1 to 10 cm in length and take on highly branched to spherical-shaped forms, depending on the species and environmental conditions (Bosence 1976, Steneck and Adey 1976, Birkett et al. 1998, Foster et al. 2013. ...
... They can accumulate and form large beds of live and/or dead maerl (Birkett et al. 1998). Individual thalli can range from 1 to 10 cm in length and take on highly branched to spherical-shaped forms, depending on the species and environmental conditions (Bosence 1976, Steneck and Adey 1976, Birkett et al. 1998, Foster et al. 2013. Their three-dimensional structure bestows them with a very important role as foundation species-species that harbor a diverse assemblage of flora and fauna (Cabioch 1969, Keegan 1974) and serve as nursery habitats for many juvenile invertebrates and fish (Grall 2002, Kamenos et al. 2004. ...
... Recent advancements in molecular biological species identification have provided important information on coralline algal diversity and distribution (Pardo et al. 2014, Hernández-Kantún et al. 2015. The distribution of the various maerl species is thought to be greatly influenced by irradiance, temperature, salinity, and substratum (Adey and McKibbin 1970, BIOMAERL Team 1998, Birkett et al. 1998. Although species with different geographic boundaries can coexist in the same location, their abundance and survival depend greatly on their environmental thresholds and plasticity to withstand variability in abiotic factors (Hurd et al. 2014). ...
Free-living red coralline algae play an important role in the carbon and carbonate cycles of coastal environments. In this study, we examined the physiology of free-living coralline algae-forming maerl beds in the Bay of Brest (Brittany, France), where Lithothamnion corallioides is the dominant maerl (i.e., rhodolith) species. Phymatolithon calcareum and Lithophyllum incrustans are also present (in lower abundances) at a specific site in the bay. We aimed to assess how maerl physiology is affected by seasonality and/or local environmental variations at the inter-and intraspecific levels. Physiological measurements (respiration, photosynthetic, and calcification rates) were performed using incubation chambers in winter and summer to compare (1) the dominant maerl species at three sites and (2) three coexisting maerl species at one site. Comparison of the three coexisting maerl species suggests that L. corallioides is the best adapted to the current environmental conditions in the Bay of Brest, because this species is the most robust to dissolution in the dark in winter and has the highest calcification efficiency in the light. Comparisons of L. corallioides metabolic rates between stations showed that morphological variations within this species are the main factor affecting its photosynthetic and calcification rates. Environmental factors such as freshwater inputs also affect its calcification rates in the dark. In addition to interspecies variation in maerl physiology, there were intraspecific variations associated with direct (water physico-chemistry) or indirect (morphology) local environmental conditions. This study demonstrates the plasticity of maerl physiology in response to environmental changes, which is fundamental for maerl persistence.
