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Variation in browsing activity by fishes among coral reef macroalgae. A principal components analysis is used to show variation in standardized bites taken from 12 macroalgal species by 6 herbivorous reef fish species. The upper section shows the similarity among algae in terms of the number of mass standardized bites received from herbivorous fishes. The fish taxa responsible for the ordination are shown by the species vector loadings on the lower panel. Each value is based on the mean of 28 feeding trials
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Few studies have examined the relative functional impacts of individual herbivorous fish species on coral reef ecosystem processes
in the Indo-Pacific. This study assessed the potential grazing impact of individual species within an inshore herbivorous
reef fish assemblage on the central Great Barrier Reef (GBR), by determining which fish species w...
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... PCA of the 12 macroalgal species revealed the vari- ation in the number of standardized bites taken from the macroalgae by the six herbivorous reef Wsh species (Fig. 2). In this analysis, the Wrst two components explained 79.2 and 14.5% of the variation in the number of standardized bites, respectively. One of the strongest divisions to arise from the PCA was the distinct separation of Sargassum sp. from all other macroalgae based on the grazing by S. canal- iculatus; S. canaliculatus' feeding was ...
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... The feeding of macroalgae by green sea turtles (Chelonia mydas) maintains algal communities in a cropped state, preventing their proliferation and expansion (Goatley et al., 2012;Wilson, 2010). A decline in herbivores and a lack of effective algae removal (top-down control) can facilitate the proliferation of macroalgae and lead to phase shifts on coral reefs toward macroalgae dominance (Mantyka & Bellwood, 2007a, 2007b. To maintain healthy reef ecosystems and restore those in decline, a frequently suggested strategy is to increase the number of grazers to mitigate algae overgrowth on coral reefs (Steneck et al., 2017;Stimson et al., 2007;Williams & Polunin, 2001). ...
... Galaxaura is among the least preferred foods for various herbivorous fishes (Loffler et al., 2015;Mantyka & Bellwood, 2007a, 2007b. Mantyka and Bellwood (2007a) found the lowest grazing frequencies and minimal biomass removal of G. filamentosa by common herbivorous fishes compared to other macroalgae. ...
... Galaxaura is among the least preferred foods for various herbivorous fishes (Loffler et al., 2015;Mantyka & Bellwood, 2007a, 2007b. Mantyka and Bellwood (2007a) found the lowest grazing frequencies and minimal biomass removal of G. filamentosa by common herbivorous fishes compared to other macroalgae. Recent field observations further suggest that, while several species of coral reef fish feed on epiphytes and epifauna from the surface of G. divaricata, they do not readily remove G. divaricata itself . ...
Galaxaura divaricata is a partially calcified macroalga that hampers coral recruitment , growth, and recovery via the excretion of allelopathic secondary metabolites. Herbivorous fishes are not major consumers of Galaxaura spp. and there is a need to understand feeding preferences for Galaxaura divaricata in other macroherbivores, like sea urchins and green sea turtles that could act as potential controlling agents. Under certain environmental conditions, G. divaricata can proliferate and overgrow degraded reefs for several years, as documented for several coral patch reefs in the lagoon of Dongsha Atoll, South China Sea. This study aimed to experimentally test the feeding preferences of five species of sea urchin and two individual green sea turtles, Chelonia mydas, for G. divaricata. Specifically, we quantified and compared the consumption rates of the allelopathic G. divaricata with Gracilaria edulis, a nonallelo-pathic, fleshy red alga, known to be highly favored by herbivores. Results showed that the five urchin species fed on both G. edulis and G. divaricata. However, urchins consumed 2-8 times less wet weight of G. divaricata (range 0.3-3.1 g urchin −1 24 h −1) compared to G. edulis (range 0.6-18 g urchin −1 24 h −1), suggesting that urchin grazing may exert some control on G. divaricata abundance but is likely ineffective for a large-scale removal of the alga. Further, both green sea turtles avoided G. divaricata and selectively fed on G. edulis. More experiments are needed to test the potential role of herbivores in controlling the overgrowth of coral competitive and allelopathic mac-roalgae, like Galaxaura on coral reefs. K E Y W O R D S allelopathic, coral reefs, feeding preference, Gracilaria edulis, herbivory, macroalgae
... However, the ability of herbivores to affect macroalgae can be in uenced by geographic variation in species susceptibility to grazing (Mantyka & Bellwood, 2007), nutrient enrichment conditions and other interacting factors (Adam et al., 2015). In the Caribbean region, ochrophytes with high chemical diversity and expression, such as those in the genus Lobophora and Dictyota (Hay, 1988), tend to dominate (Dell et al., 2020, Vieira et al., 2020. ...
Tropical macroalgae serve importance ecological roles on coral reefs but can supplant corals in phase shifts as shown worldwide. Thus, it is important to understand their fundamental photophysiology and effects on calcification mechanisms. We examined organic δ¹³C, inorganic CaCO3 δ¹³C and δ¹⁸O, and organic %C, %N, C:N of abundant macroalgae on Little Cayman Island (LCI) reefs across a broad light gradient (5–2,000 μmol photons m⁻² s⁻¹). We hypothesized that LCI macroalgae utilize greater CO2 in low light environments as carbon concentration mechanisms (CCMs) to take up HCO3⁻ have high energetic costs. We proposed that calcification mechanisms are also influenced by light and Ci-use strategies. LCI macroalgae had organic δ¹³C values (-12‰ to -25‰) indicative of CCMs and exhibited only a 1–3‰ δ¹³C depletion under irradiances < 5 μmol photons m⁻² s⁻¹. Light and phyla were significant in a mixed model explaining ~ 80% of variance in organic δ¹³C. Organic δ¹³C was a weak predictor and light insignificant in explaining inorganic δ¹³C values of thalli carbonates. Biogenic carbonate δ¹³C values were taxa-specific based on cluster analysis of δ¹³C:δd¹⁸O ratios, an indication of diverse calcification mechanisms. LCI macroalgal photosynthesis utilized CCMs across a broad range of irradiances, thus greater CO2 availability under ocean acidification is not likely to enhance community dominance of macroalgae of concern (e.g., Lobophora sp.) due to shifts in photophysiology. The mechanisms of Ci sequestration for photosynthesis appeared to be mostly uncoupled from calcification mechanisms that were diverse across phyla, likely due to distinct macroalgal forms, sites of calcification and carbonate structure.
... However, the ability of herbivores to affect macroalgae can be in uenced by geographic variation in species susceptibility to grazing (Mantyka & Bellwood, 2007), nutrient enrichment conditions and other interacting factors (Adam et al., 2015). In the Caribbean region, ochrophytes with high chemical diversity and expression, such as those in the genus Lobophora and Dictyota (Hay, 1988), tend to dominate (Dell et al., 2020, Vieira et al., 2020. ...
Tropical macroalgae serve importance ecological roles on coral reefs but can supplant corals in phase shifts as shown worldwide. Thus, it is important to understand their fundamental photophysiology and calcification mechanisms. We examined organic d ¹³ C, organic+inorganic d ¹⁵ N, inorganic CaCO 3 d ¹³ C and d ¹⁸ O, and organic %C, %N, C:N of abundant macroalgae on Little Cayman Island (LCI) reefs across irradiance gradients (5-2,000 mmol m ⁻² s ⁻¹ ). We hypothesized macroalgae utilize greater CO 2 in low light as carbon concentration mechanisms (CCMs) for HCO 3 ⁻ uptake have higher energetic costs. We proposed that calcification mechanisms are influenced by light and Ci-use strategy in addition to taxonomy. LCI macroalgae had organic d ¹³ C values (-12‰ to -25‰) indicative of CCMs and exhibited only 1-3‰ ¹³ C depletion in irradiances <5 mmol photons m ⁻² s ⁻¹ . Ochrophyte d ¹³ C values were enriched in ¹³ C at low nitrogen indicative of efficient CCMs. Macroalgae exhibited four clusters of thalli CaCO 3 d ¹³ C that were distinctly taxon-specific. Rhodophytes exhibited the most negative inorganic d ¹³ C and d ¹⁸ O values (-4.1‰ ± 0.7‰; -3.7‰ ± 0.4‰) an indication of high calcifying space pH and rapid calcification, potentially reliant on active ion transport. Relatively higher organic C fractionation when utilizing greater CO 2 for photosynthesis was reflected in depleted thalli carbonates in species/genus with positive d ¹³ C values. Increasing ocean CO 2 is not likely to enhance dominant LCI macroalgal photosynthesis as these reef macroalgae utilize CCMs across a broad range of irradiances; however, effects on calcification may be taxon specific based on the degree of biotic control elucidated in thalli carbonate isotopes.
... Videos were checked for visible "bites", defined as contact between fish mouth and algae, to determine grazing intensity. Rapid bites in quick succession that could not be separated were counted as a single bite (Mantyka and Bellwood, 2007;Korzen et al., 2011). For each bite, the conducting fish was identified up to species level and categorized using visual estimation of total length (TL) in size classes of 5 cm (0-5, 5-10, etc). ...
Fish assemblages of different types of artificial reefs can differ greatly in abundance, biomass and composition, with some reef types harboring over five times more herbivores than others. It is assumed that higher herbivorous fish abundance results in a higher grazing intensity, affecting the benthic community by means of enhanced coral recruitment, survival and growth. Territorial fish species might affect this process by chasing away other fish, especially herbivores. In this study we compared the fish assemblage, territorial behavior and grazing intensity by fish on two artificial reef types: reef balls and layered cakes, differing greatly in their fish assemblage during early colonization. In addition, the effect of artificial reef type on benthic development and coral recruitment, survival and growth, was investigated. Although layered cakes initially harbored higher herbivorous fish biomass, this effect was lost during consecutive monitoring events. This seems to be the result of the higher territorial fish abundance around the layered cakes where almost four times more chasing behavior was recorded compared to the reef balls. This resulted in a more than five times lower fish grazing intensity compared to the reef-ball plots. Although macroalgae were effectively controlled at both reefs, the grazing intensity did not differ enough to cause large enough structural changes in benthic cover for higher coral recruitment, survival or growth. The high turf algae cover, combined with increasing crustose coralline algae and sponge cover likely explained reduced coral development. We recommend further research on how to achieve higher grazing rates for improved coral development on artificial reefs, for example by facilitating invertebrate herbivores.
... A reduction in coral biomass leads to algal overgrowth (Hodgson, 1999), which reduces reef structure complexity and potentially affects the feeding of coral reef fish (McCormick et al., 2017), and the coral-algal phase shift would reduce biodiversity and ecosystem maturity (Ainsworth and Mumby, 2015). Although, there is no doubt that the potential importance of individual herbivorous species in removing macroalgae from coral reefs (Mantyka and Bellwood, 2007), the process of macroalgal removal would be strongly influenced by coral reef conditions (Chong-Seng et al., 2014). Cheal et al. (2010) suggested that coral reefs could lose resilience even under relatively low fishing pressure on herbivorous fishes. ...
Qilianyu Islands coral reefs (QICR), located in the northeastern part of the South China Sea, has been affected by human activities and natural disturbance. To characterize the trophic structure, ecosystem properties and keystone species of this region, a food-web model for the QICR is developed using methods involving a mass-balance approach with Ecopath with Ecosim software. Trophic levels range from 1.00 for detritus and primary producers to 3.80 for chondrichthyes. The mean trophic transfer efficiency for the entire ecosystem is 13.15%, with 55% of total energy flow originating from primary producers. A mixed trophic impact analysis indicates that coral strongly impacts most components of this ecosystem. A comparison of our QICR model with that for other coral reef ecosystems suggests that the QICR ecosystem is immature and/or is degraded.
... Herbivorous fishes, those fishes that feed on benthic microalgae, filamentous algae, and macroalgae as well as on a variety of organisms (e.g., Crossman et al., 2005), are important drivers of community dynamics on coral reefs, influencing the abundance of algae and their competitive interactions with corals (Hughes et al., 2007;Adam et al., 2015a;Zaneveld et al., 2016). Different species of herbivorous fish, such as parrotfishes, surgeonfishes, and rabbitfishes, often feed on different suites of algae (Mantyka and Bellwood, 2007;Burkepile and Hay, 2008;Hoey and Bellwood, 2009). Thus, as herbivore species diversity increases, the ability of any given alga to escape or deter all herbivores declines (Hay et al., 1994;Rasher et al., 2013), suggesting that herbivore diversity is a critical component of how herbivory impacts benthic communities on reefs (Cheal et al., 2010;Rasher et al., 2013;Lefcheck et al., 2019). ...
... This pattern suggests that the herbivore species that frequently browse macroalgae feed on a wide suite of algae, with some algae fed on by as many as 6-8 species of herbivorous fish (Fig. S1). Past studies using similar cafeteria-style feeding assays have suggested strong complementarity in feeding on macroalgal species (e.g., Mantyka and Bellwood, 2007;Burkepile and Hay, 2008;Rasher et al., 2013). The fact that we used 5-10× more algal species than previous studies allowed us to document the underappreciated redundancy that there appears to be among macroalgal-feeding parrotfishes and surgeonfishes. ...
Understanding how functional traits drive plant-herbivore interactions often illuminates the mechanisms driving niche partitioning and functional diversity in this important guild of consumers. On coral reefs, a diverse suite of herbivorous fishes is key for controlling algal abundance and impacting benthic community dynamics. Here, we focus on how algal traits shape complementarity in feeding for a diverse suite of large herbivorous fishes on a coral reef in the wider Caribbean. We used feeding assays in the field to document feeding patterns of the different herbivorous fishes across 50 species of macroalgae. Then, we used a suite of macroalgal traits such as dry mass, nutrient content, calcification, and chemical defenses to assess how these traits influenced patterns of consumption. Algal defenses were the major traits determining the overall vulnerability of algae to herbivores, with uncalcified algae from undefended genera being consumed 40% more rapidly than algae that were either calcified or chemically defended. Nutrient content of algae explained little in patterns of overall herbivory. We found significant niche diversification in feeding both among and within genera with the three major genera having unique feeding patterns on different suites of algae (Acanthurus spp. - red macroalgae, Sparisoma spp. - brown and green macroalgae, and Scarus spp. - benthic filamentous algae). With respect to how algal traits influenced patterns of feeding in individual species, we found that: (1) some herbivore species were almost exclusively influenced by avoiding algal defenses, (2) some species showed strong interactions between algal defenses and nutrient content that determined their feeding, and (3) some species (Kyphosus spp., Pomacanthus arcuatus) targeted chemically-defended algae with high nutrient content. Our work highlights the role that algal traits play in influencing patterns in the diversity and redundancy of feeding in herbivorous fishes on coral reefs.
... Kodingareng Lompo yang merupakan organisme produser memberikan sumbangan berarti bagi kehidupan binatang akuatik terutama organisme-organisme herbivora di perairan laut (Mantyka & Bellwood 2007). Tidak hanya itu makroalga ini memiliki manfaat ekologi penstabil siklus nutrient, dan sebagai habitat dari beberapa jenis crustacea, polychaetes, echinodermata dan gastropoda. ...
Based on the results obtained from this study, it can be concluded that: (1). Halimeda sp density based on stations, there is a noticeable difference between station 1 and station 3, (2)Halimeda sp density based on the research time, namely there is a noticeable difference between the study time in July and October, (3) Padina sp density based on stations, there is a noticeable difference between station 1 and station 2, and (4). The density of Padina sp is based on the time of the study, that is, there is a noticeable difference between the time of the study in July and October.
... Galaxaura is sparingly consumed by macroalgae-eating herbivores such as Siganidae (rabbitfishes), Acanthuridae (surgeon fishes), and Kyphosidae (sea chubs) likely due to its poor nutritional value and production of secondary metabolites (Mantyka & Bellwood, 2007a, 2007bRasher & Hay, 2014;Rasher et al., 2013). However, many such feeding selectivity experiments use transplanted macroalgae, i.e., presenting different types of seaweeds in a "cafeteria style" array in habitats where these seaweeds may be uncommon (Mantyka & Bellwood, 2007a, 2007bRasher et al., 2013). ...
... Galaxaura is sparingly consumed by macroalgae-eating herbivores such as Siganidae (rabbitfishes), Acanthuridae (surgeon fishes), and Kyphosidae (sea chubs) likely due to its poor nutritional value and production of secondary metabolites (Mantyka & Bellwood, 2007a, 2007bRasher & Hay, 2014;Rasher et al., 2013). However, many such feeding selectivity experiments use transplanted macroalgae, i.e., presenting different types of seaweeds in a "cafeteria style" array in habitats where these seaweeds may be uncommon (Mantyka & Bellwood, 2007a, 2007bRasher et al., 2013). Fish are generally opportunistic and will often try novel foods when these suddenly appear in their habitat (Wulff, 2021). ...
... Galaxaura is infrequently consumed by herbivorous fishes, likely because its high calcium carbonate content that diminishes its nutritional value to most species (Bonaldo & Hay, 2014;Hay, 1986;Littler et al., 2006;Lobel, 1981;Loffler et al., 2015aLoffler et al., , 2015bMantyka & Bellwood, 2007a). Hence, allelopathic and nutrient-poor macroalgae such as G. divaricata are not targeted by common herbivores (e.g., rabbitfish, surgeon fishes, sea chubs) and once established are likely to dominate reef habitats for several years (Nieder et al., 2019). ...
In degraded coral reef ecosystems, allelopathic macroalgae have received increasing attention from marine ecologists because their secondary metabolites (also known as allelochemicals) kill corals that grow adjacent to them and weaken the recovery of degraded reefs. One well-known coral-killing macroalga is the calcareous red seaweed Galaxaura. However, our knowledge of how coral reef fishes interact with allelo-pathic algae like Galaxaura is very limited. Here, we documented novel observations of feeding interactions of 17 species of coral reef fishes (herbivorous and carnivorous) with the filamentous Galaxaura divaricata on degraded lagoon patch reefs in Dongsha Atoll (South China Sea). Video analyses showed that territorial farming damselfishes (i.e., Dischistodus perspicillatus, D. prosopotaenia, Hemiglyphidodon plagiometopon, Pomacentrus grammorhynchus, P. adelus, and Neoglyphidodon nigroris) and juvenile par-rotfishes (Scarus schlegeli, S. ghobban, S. rivulatus, and Chlorurus spilurus) likely used G. divaricata as a feeding substratum. Further, microscopic analyses revealed that the filamentous surface of G. divaricata harbored a wealth of epiphytic microalgae, such as filamentous cyanobacteria (i.e., Leptolyngbya, Lyngbya, Rivularia, Oscillatoria, and Stigonema), diatoms (i.e., Synedra, Nitzschia, Mastogloia, and Pleurosigma), and fil-amentous red algae (i.e., Heterosiphonia), suggesting that these fishes targeted the nutrient-rich microscopic epiphytes rather than the nutrient-poor host. Juvenile ben-thic carnivores (i.e., Labridae, Parupeneus multifasciatus, and Meiacanthus grammistes) form feeding assemblages with roving parrotfishes to feed on small invertebrates (i.e., amphipods, copepods, isopods, gastropods, and polychaetes) associated with G. di-varicata. Given that coral reef fishes appear to target the epiphytes associated with Galaxaura rather than the alga itself, these observations thus substantiate the threat posed by the overgrowth of G. divaricata to coral recovery in degraded reef systems due to the lack of natural grazers.
... roving grazers and harvest algae inside the territory. Both groups influence benthic community structure in different ways (Ceccarelli 2007;Clements et al. 2009;Eurich et al. 2018;Goatley and Bellwood 2010;Mantyka and Bellwood 2007;Mumby et al. 2006). ...
... These interactions are ones that may result from cleaners' numerous beneficial effects on their fish clients, one effect being a higher abundance of some territorial algal farming and roving grazing fish functional groups (Grutter et al. 2020b). Fish grazing enhances certain algae and reduces other algae, detritus, and sediment (Ceccarelli 2007;Clements et al. 2009;Eurich et al. 2018;Goatley and Bellwood 2010;Mantyka and Bellwood 2007;Mumby et al. 2006). We hypothesized a higher abundance of grazers, due to cleaners' presence, would result in a higher grazing density (bites area −1 ) with consequences for the benthos (i.e., fouling material on tiles). ...
... We found that grazing density on tiles and the natural benthos was sustained primarily by fish functional groups known to affect the benthos, specifically, territorial indeterminate farmers and the roving sediment-remover (detritivore), Ctenochaetus striatus (Ceccarelli 2007;Clements et al. 2009;Eurich et al. 2018;Goatley and Bellwood 2010;Mantyka and Bellwood 2007;Marshell and Mumby 2015). Yet, grazing density was not affected by the presence of the cleaner fish Labroides dimidiatus that had been manipulated for 10 years. ...
Grazing fishes farm algae, and consume algae, detritus and sediment and consequently differentially modify benthic communities. Manipulations of cleaner fish Labroides dimidiatus on reefs show that cleaners affect fish abundance differently according to grazer functional group. Accordingly, whether reefs are grazed differently, with consequences for the benthos (fouling material tile⁻¹), was tested using reefs kept free of L. dimidiatus for 10 years compared with undisturbed control reefs. We recorded on video the grazing density (bites tile⁻¹ h⁻¹ reef⁻¹) on settlement tiles and the natural benthos (roving fishes only), according to territorial algal farmer (Pomacentridae) and roving grazer (Acanthuridae, Labridae, Siganidae) functional groups, and measured the accumulation of fouling material tile⁻¹ after 10 months. Grazing density on tiles (dominated by ‘indeterminate’ farmers, and roving ‘sediment-removing’ detritivore Ctenochaetus striatus) and the natural benthos (dominated by Ct. striatus and other grazers) was not measurably affected by cleaner presence. The composition of fouling material (dominated by detritus > turf algae > sediment > other) and organic and inorganic dry weight of material tile⁻¹ were also not measurably affected by cleaner presence. This points to resilience of the benthic community to loss of cleaners. The likely complex interactions between cleaner fish presence, grazer abundance and mobility, and the often-opposite effects of territorial farmers and roving grazers on the benthos underscore the challenge in determining indirect effects of cleaners on benthic community structure. However, a lack of cleaners has negative ramifications for fish populations and physiology and thus their loss remains problematic for client fishes.
... Herbivorous fish feeding activity also varies spatially in reef systems and is typically highest in shallow habitats on offshore reefs (Russ 1984;Brokovich et al. 2010;Cheal et al. 2013). The influence of each of these variables on macroalgae depends on morphological and taxonomic differences in requirements for light (Markager and Sand-Jensen 1992;Leukart and Lüning 1994;Gómez and Huovinen 2011) and water quality (McCook et al. 1997;Schaffelke and Klumpp 1998;Umar et al. 1998), as well as susceptibility to wave dislodgement (Dudgeon and Johnson 1992;Starko et al. 2015) and herbivory (Hay 1981a;Marques et al. 2006;Mantyka and Bellwood 2007). ...
Context. Although increases in macroalgal cover on coral reefs are often reported alongside declines in coral, the composition of algal assemblages and their spatial dynamics are not commonly investigated.
Aims. To quantify changes in macroalgal assemblage composition over two spatial environmental gradients, depth and distance from shore, within a nearshore reef system in Kimbe Bay, Papua New Guinea, where coral cover has declined.
Methods. Benthic cover was quantified at three depths (reef flat,10 and 15m) on the windward reef slopes of six reefs located three distances from shore (fringing reefs, and platform reefs 100–200m and 0.7−1km offshore).
Key results. Macroalgal cover was highest on the reef flat, and assemblage composition varied among depths and distances from shore. Macroalgal cover was not correlated with coral cover except where macroalgal cover was greater than 20%, where a negative correlation occurred. There was no correlation between macroalgal cover and turf algal cover. All three benthic groups were negatively correlated with the combined total cover of sand and gravel.
Conclusions. These results indicated a fine-scale spatial structure of macroalgal assemblages on coral reefs over a narrow depth range and short distance from shore and highlighted the importance of a solid substratum.
Implications. It is likely that the ecological interactions between corals and macroalgae vary considerably over narrow spatial gradients.
