Abundance Of Herbivorous Fishes Research Articles

Variation in population assemblage of Acanthuridae and Scaridae across human concentration levels during a bleaching event affecting the coral reefs of Guna Yala, Panama

Abstract Coral reefs are the ocean's most productive ecosystem, supporting a huge amount of biodiversity, and are relied upon by millions of people worldwide. As we progress into the Anthropocene, coral reef ecosystems are increasingly threatened by a swath of pressures. Of the most impactful are El-Niño Southern Oscillation-related heat pulses, which result in the bleaching and potential mortality of coral reefs. Bleaching events, in synergy with other threats, are increasing algal-dominated reefs, which impact the productiveness of coral reef ecosystems. Herbivorous fish are the prominent algal consumers and are essential in controlling algal blooms. Species from the family Acanthuridae and Scaridae are the most conspicuous of herbivorous fish on coral reefs, and through a diverse array of physiological differences compose several unique functional groups. The population distribution of Acanthuridae and Scaridae are directly correlated with coral reef characteristics and composition and can suffer from bleaching events as well. Despite their importance in maintaining reef health and improving resilience to disturbances, there is a very scarce collection of literature that describes the population assemblage of Acanthuridae and Scaridae spp. during bleaching events. This study aims to contribute to this underreported phenomenon. Visual surveys of Acanthuridae and Scaridae species were conducted to measure the average density, mean size, and biomass in terms of coral reef characteristics across a human concentration gradient in Guna Yala, Panama. Results suggest a similar overall abundance of herbivorous fish between the two reef locations, with significantly larger sizes and biomass of A. coeruelus, S. aurofrenatum, S. viride, and S. iseri in reefs further away from human concentration. This correlates with significantly higher rugosity on these reefs. The mean size of each respective species appears to be lower than previously reported across the Caribbean. Additionally, the biomass distribution was strikingly skewed by S. viride which corresponds to almost ¾ of the total biomass. This indicates that the current bleaching event is having drastic impacts on the distribution of herbivorous fish populations, which is exacerbated by proximity to human concentration. This can have very negative consequences for the recovery of these reefs following the bleaching event. Of specific concern are the coral reefs closer to humans. Data from benthic composition surveys show that macroalgae cover and overall coral bleaching are significantly higher compared to reefs far from humans. This study provides vital information that may be useful for future studies to identify coral reef resilience to bleaching events through the scope of Acanthuridae and Scaridae population distribution. Lay Summary The ocean is a crucial and largely unexplored part of our planet. One area that has begun to receive sufficient scientific attention is coral reefs. This is because, despite only covering less than 1% of the ocean’s surface, coral reefs support a quarter of all marine life. This rich environment provides more than a billion people with their primary source of protein and offers coastal protection to hundreds of millions of people. However, the future of coral reefs is under threat. Due to climate change and human pressures, coral reefs are facing mortality on a worldwide scale. Of the most lethal are bleaching events, when the water temperature rises past the threshold of coral, and they turn white and die. At the same time, corals face a daily threat from increasing algae coverage, which can smother and kill the coral. These threats have intensified in the recent few decades and may permanently alter the biodiversity and productivity of coral reefs. Understanding these changes is of utmost importance, and one way to do so is to study the animals that eat algae and give coral a chance to thrive—herbivorous fish. This paper analyzes the population distribution of two herbivorous fish families: Acanthuridae (surgeonfish) and Scaridae (parrotfish) during a bleaching event. Learning how a bleachingevent can impact the presence of these essential species among coral reefs has rarely been accomplished in scientific literature, so this paper offers valuable contributions to a more comprehensive understanding of reef health during bleaching events and our changing world.

Distribution and abundance of herbivorous reef fishes on a barrier reef system in the Florida Keys and Dry Tortugas, Florida

Herbivorous reef fishes control algal growth and are critical for maintaining reef health. Grazing effects vary due to community composition, so a diverse herbivore community is important for preventing phase shifts from coral to algal-dominated reefs. However, herbivore communities and grazing effects vary spatially, resulting in non-uniform distribution of algal mitigation across the seascape. Therefore, understanding how habitat influences herbivore communities is essential for predicting the spatial distribution of these species' ecological services. This study used underwater visual surveys (n = 5455) to examine how habitat influences spatial patterns of herbivorous fish densities and species richness in the Florida Keys and Dry Tortugas, Florida. Herbivorous fishes were ubiquitous, and communities were dominated by small herbivores such as damselfishes (Pomacentridae), gobies (Gobiidae), surgeonfishes (Acanthuridae), and small- to medium-bodied parrotfishes (subfamily Scarinae). A suite of factors influenced herbivorous fish communities but boosted regression tree results showed that habitat relief, depth, and spatial location within the Florida Keys and Dry Tortugas were the most important factors. In general, herbivore occurrence, density, and species richness increased as percent of low relief hardbottom habitat (<0.2 m high) decreased. In addition, density and occurrence of herbivores generally increased at shallower depths. Spatial location influenced the density of herbivores with potential hotspots predominantly located in the Upper Keys and the Dry Tortugas Bank. These data provide a valuable understanding of the spatial distribution of herbivorous reef fishes, and aid management decisions regarding the protection and sustainability of herbivore resources and the ecosystems that rely on them.

Dynamic of coral recruits in the Karimunjawa National Park, Central Java, Indonesia

Abstract. Tarigan SAR, Munasik, Wijayanti DP, Muhidin, Rohman EA, Pardede S. 2024. Dynamic of coral recruits in the Karimunjawa National Park, Central Java, Indonesia. Biodiversitas 25: 869-880. After a disturbance event, coral reefs can recover naturally by recruiting new corals. These can be affected by environmental factors like the substrate's physical and biological structure, predation, and accidental mortality of recruits by grazers, as well as the number and size of parent corals supplying larvae. This study examined the connection between newly recruited corals and biological factors such as sea urchin density, herbivorous fish abundance, and hard coral coverage. The study was monitored changes in coral cover, juvenile coral density, herbivore abundance, and hard coral coverage at 43 locations and two depths (shallow; 2-3 m) and deep (8-10 m) from 2013 to 2022. The locations were distributed across six different zone systems: the core zone, protection zone, tourism zone, traditional fisheries zone, aquaculture zone, and rehabilitation zone. Multiple Linae Regression, ANOVA test, and Principal Component Analysis were employed to assess the relationship between coral recruitment and other variables. Results indicated that the coral recruitment density was not significantly different when comparing different zoning systems (two-way ANOVA test, P-value>0.05). Based on the PCA analysis, we found that in 2013 and 2019, excavator, sea urchin, browser, and hard coral have a positive relationship with coral recruitment, which implies that coral recruitment would increase as sea urchin, browser, and hard coral increase. Meanwhile, in 2019 and 2022, coral recruitment has a negative relationship with scraper, and also with hard coral growth (although only in 2022), implying that coral recruitment would decrease if scraper and hard coral increase. The study recommends restoring the role of herbivorous species in Karimunjawa National Park (KNP) by prioritizing them in conservation efforts and managing their populations.

Dynamics of Herbivorous Fish and Its Role in Controlling Algal Coverage in Coral Reef Restoration Area Affected by the Bleaching Phenomenon in 2016

Coral reefs in the waters of Liukangloe Island were reported to have experienced a bleaching phenomenon in May 2016 and rehabilitation efforts were carried out in 2019. This study aimed to analyze the structure of the herbivorous fish community and its role in controlling algal cover in the rehabilitation area. Observations of herbivorous fish were carried out using visual census techniques on an area of ​​4m2 and observation of algae in 0.5x0.5 m2 transects on several coral attachment media from dead coral substrates. The results showed that the proportion of herbivorous fish species in the transplant area ranged from 15.81-58.67% and the proportion of individuals ranged from 12.51-34.62%. The dynamics of the number of species and abundance of herbivorous reef fish did not show significant differences between substrates and had the same dynamic pattern in all substrates uses but varied temporally according to the time of observation. The exception is the rubble area which continues to increase until the end of the observation. A high number of herbivorous fish species richness was observed in the branching and natural coral substrates and low in the rubble substrate. The abundance of herbivorous reef fish showed a significant and negative relationship to algal cover and confirmed that the presence of herbivorous reef fish could control or reduce the value of algal cover.

The effect of artificial reef design on the attraction of herbivorous fish and on coral recruitment, survival and growth

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.

Persistent thermally driven shift in the functional trait structure of herbivorous fishes: Evidence of top-down control on the rebound potential of temperate seaweed forests?

Extreme climatic events can reshape the functional structure of ecological communities, potentially altering ecological interactions and ecosystem functioning. While these shifts have been widely documented, evidence of their persistence and potential flow-on effects on ecosystem structure following relaxation of extreme events remains limited. Here, we investigate changes in the functional trait structure - encompassing dimensions of resource use, thermal affinity, and body size - of herbivorous fishes in a temperate reef system that experienced an extreme marine heatwave (MHW) and subsequent return to cool conditions. We quantify how changes in the trait structure modified the nature and intensity of herbivory-related functions (macroalgae, turf, and sediment removal), and explored the potential flow-on effects on the recovery dynamics of macroalgal foundation species. The trait structure of the herbivorous fish assemblage shifted as a result of the MHW, from dominance of cool-water browsing species to increased evenness in the distribution of abundance among temperate and tropical guilds supporting novel herbivory roles (i.e. scraping, cropping, and sediment sucking). Despite the abundance of tropical herbivorous fishes and intensity of herbivory-related functions declined following a period of cooling after the MHW, the underlying trait structure displayed limited recovery. Concomitantly, algal assemblages displayed a lack of recovery of the formerly dominant foundational species, the kelp Ecklonia radiata, transitioning to an alternative state dominated by turf and Sargassum spp. Our study demonstrates a legacy effect of an extreme MHW and exemplified the value of monitoring phenotypic (trait mediated) changes in the nature of core ecosystem processes to predict and adapt to the future configurations of changing reef ecosystems.

The abundance of herbivorous and coralivorous fishes during and after coral bleaching in Krueng Raya Waters, Aceh Besar District

This study aims to determine the community structure changes and to determine the abundance of herbivorous fish and coralivorous fish in Krueng Raya waters during and after the occurrence of coral bleaching. This research was conducted in three stages: June 2016, October 2016, and February 2017. There are 3 locations for data collection, including Benteng Inong Balee, Ahmad Rhang Manyang, and Lhok Mee in Mesjid Raya Sub-District, Aceh Besar District. Reef fish abundance data were collected at a depth of 36 meters using the visual census technique (VCT) -belt transect method. The study results show that there were six families, 17 genera, and 47 species belonging to the herbivorous and coralivorous fish groups. The mostabundantfamilywasthe Chaetodontidae family,while the leastfishfamily wasthe Kyphosidae family. The highest abundance of corallivorous fish was found at station 2 in October 2016, with a value of 509 ind/ha. The lowest was found at station 3 in October 2016, with a value of 182 ind/ha. The highest abundance of herbivorous fish was found at station 3 in February 2017, with a value of 498 ind/ha. The lowest was found at station 3 in October 2016, with a value of 150 ind/ha.

Assessing of coral reef resilience on Lembeh Island, North Sulawesi

Resilience is the ability of a system to reach equilibrium after a temporary disturbance. When an ecosystem is disturbed, then the recovery of the system is very dependent on the diversity of species that are still left. The remaining communities determine the direction of new successional communities formed after the disturbance has passed, including coral, fish, and other biota communities. This study aimed to determine the level of resilience of coral reef ecosystems on Lembeh Island. The observation was carried out from January 16-19, 2019, at a 7-meter depth. Determination of the coral reef index will refer to coral reef resilience index table. It is found that the resilience of coral reefs on Lembeh Island currently has a high potential for recovery (resilience) from natural stressors based on the 16 parameters. Seven parameters have very high resilience values: the proportion of bleaching resistant species, community resistance to bleaching, taxonomic diversity, size/age distribution, the abundance of reef fish on live coral, and the abundance of coral benthos on live coral and coral disease levels. Lembeh Island is dominated by hard corals measuring between 5.1 to 25 cm (size M) by ~46%, then sizes more than 25 cm (size L) by ~37% and juvenile size (size S) by 17%. The coral health index on Lembeh Island has the capacity to recover if the condition of coral cover is minimally maintained or improved and lower fleshy seaweed cover by increasing the abundance and biomass of herbivorous fish.

Diversity of reef fish on Lembeh Island as an indicator of the coral reef health condition

Lembeh Strait in North Sulawesi is one of the areas included in the world’s coral triangle. Coral reef structures provide a habitat for reef fish. Herbivorous and invertivorous fish were essential to determine the direction of coral reef succession. This study aims to examine the health of coral reefs based on the presence of reef fish. Observations were conducted on January 16-19, 2019, with a total of 22 observation points. Observation of reef fish communities using the underwater visual census (UVCs) and belt transect method. At the observation site, it was found that there were 260 species of reef fish. The resilience of coral reefs based on the presence of reef fish has a high value on the parameters of the abundance of herbivorous fish, taxonomic diversity, and abundance of coral reef fish.

Reduction in Cover of Two Introduced Invasive Macroalgae by Herbivores on Coral Reefs of Kāne‘ohe Bay, Hawai‘i1

Two introduced invasive red macroalgae, Eucheuma denticulatum (Burman) Collins & Hervey and Gracilaria salicornia C. Ag., progressively declined in abundance in Kāne‘ohe Bay, Hawai‘i, following ∼30 years of increase since their introduction in the mid-1970s. The declines were not the result of biological control or mechanical control efforts, but instead were the result of grazing by native herbivores, probably fishes, as demonstrated by field experiments conducted in 2014 with algal thalli exposed to, and protected from grazing. Two long-term time-series of the abundance of herbivorous fishes at Kāne‘ohe Bay patch and fringing reef sites indicated that the abundance of herbivorous fishes increased from 2007 through 2014 over the period when these macroalgae declined in cover. Analyses of data of algal cover from surveys of Kāne‘ohe Bay reefs carried out between 1996 and 2018 indicate that the declines in E. denticulatum and G. salicornia began in approximately 2008, several years before control programs commenced on some of the reefs in the bay. In addition to intense herbivory, high summer water temperatures in 2014 and 2015 may have contributed to the decline in E. denticulatum. Naturally occurring declines in the abundance of alien invasive marine algal species have rarely been reported in the literature. These reductions in macroalgal abundance are the second instance of decline in invasive macroalgae in Kāne‘ohe Bay since 2006, and have reduced competition between macroalgae and corals on reef flats and reef slopes across the bay.

A global meta‐analysis of temperature effects on marine fishes’ digestion across trophic groups

AbstractAimThe temperature constraint hypothesis proposes that marine herbivorous fishes are rare at high latitudes relative to carnivorous fishes because low temperatures impair the digestion of plant material. To test this hypothesis, we compared the effects of temperature on the digestive performance and investment in digestion of marine fishes across trophic groups.LocationGlobal marine ecosystems.Major taxa studiedMarine fishes.MethodsWe analysed data from 304 species consuming a range of diets to quantify the effects of temperature on three indicators of digestive performance and investment: gut passage time, absorption efficiency, and gut length.ResultsDecreasing temperatures increase gut passage time in fishes consuming macroalgae more than fishes consuming other fish or invertebrates. Low temperatures do not impair absorption efficiency in fishes regardless of diet, but herbivores have lower absorption efficiencies than carnivores overall. Gut length decreases with decreasing temperature in all trophic groups.Main conclusionsOur analyses reveal limited evidence to support the temperature constraint hypothesis. Low temperatures slow digestion more in fishes consuming macroalgae than those consuming animal prey; however, this may not reflect a meaningful disadvantage for herbivores but rather could be explained by greater representation of fishes relying on microbial fermentation at high latitudes. Herbivorous fishes absorb nutrients and energy from their food in similar proportions regardless of temperature, in contrast to the expectations of the temperature constraint hypothesis. Decreased gut length was associated with decreasing temperature across all trophic groups, likely due to improved food quality at high latitudes, which should benefit all trophic groups by reducing their required investment in gut tissues. Altogether, our findings run counter to the general hypothesis that low temperatures disadvantage the digestion of plant material and suppress the diversity and abundance of herbivorous fishes at high latitudes.

The effect of coral reef degradation on the trophic structure of reef fishes from Bahía Culebra, North Pacific coast of Costa Rica

Fishes play numerous key ecological roles that are critical for maintaining the structure and function of coral reefs. Natural and anthropogenic disturbances can produce structural changes in coral reef habitats, which consequently may affect the trophic structure and dynamics of reef fish assemblages. Therefore, changes in the coral cover of coral reefs, caused by disturbance events can impact the abundance of reef fishes. This study determined the effect of habitat degradation on the trophic structure of coral reef fishes from Bahia Culebra, a bay located in the north Pacific of Costa Rica. We examined whether spatial and temporal changes in live coral cover (LCC) and substrate type between two periods (1995–1996 and 2014–2016) influenced the trophic structure of coral reef fishes. While planktivorous fishes maintained similar abundances between periods, omnivorous fishes (mainly facultative corallivores) were less abundant in sites with low LCC. There was a decline in abundance of mesopredators (e.g. sharks, groupers, snappers), probably because of both shelter loss and overfishing. Macroalgae feeders, herbivores-detritivores and invertivores showed high abundance in disturbed coral reefs, which could be related to predator decline or to increased algal resource abundance. Despite high abundance of herbivorous fishes, high macroalgae coverage persisted during the 2014–2016 period. The results from this study suggest that degradation of coral reef habitats from Bahia Culebra have affected the trophic structure of reef fish assemblages, and potentially the functioning of this coastal ecosystem.

Multifunctionality of an Urbanized Coastal Marine Ecosystem

Coastal marine ecosystems provide numerous invaluable services and benefits to humankind. However, urbanization of coastal areas has homogenized and reduced the biodiversity of the surrounding marine environment and the sustainability of the multiple ecosystem services it provides. Studies have focused on single ecosystem functions despite human populations relying on several functions being delivered at once (known as multifunctionality). This study investigates five ecosystem functions (primary productivity, herbivory, predation, organic matter decomposition and carbon sequestration) and overall multifunctionality in four sites along a gradient of 16 environmental parameters. Ecosystem function varied significantly between sites that were farthest apart. In determining factors that drove ecosystem functioning, we found a positive relationship between coral cover and primary productivity but negative relationships between coral cover and levels of herbivory and predation intensity. Higher temperatures and greater concentrations of chlorophyll-a had a positive impact on predation and herbivory, respectively. Notably, we found a significant negative impact of total inorganic nitrogen and significant positive impact of total Kjeldahl nitrogen on carbon sequestration. Further, individual functions were compared with fish abundance (obtained from seawater eDNA), and benthic community composition (obtained from plate % coverage of autonomous reef monitoring structures). Increasing herbivorous fish abundance had a positive impact on Ulva mass loss. Overall, relative abundance of predatory, omnivorous and planktivorous fish exerted overriding influences on primary productivity and predation intensity, implying that fishing pressure and marine protected area status are important factors. Importantly, we found significant effects from environmental parameters indicating that reliably predicting the effects of future anthropogenic impacts will not be straightforward as multiple drivers are likely to have complex effects. Taken together, urbanized coastal ecosystems exhibit varying levels of multifunctionality depending on the extent of human impact, and the functional diversity of the benthic community present.

Different environmental variables predict distribution and cover of the introduced red seaweed Eucheuma denticulatum in two geographical locations

In this study we examined abiotic and biotic factors that could potentially influence the presence of a non-indigenous seaweed, Eucheuma denticulatum, in two locations, one outside (Kane’ohe Bay, Hawai’i, USA) and one within (Mafia Island, Tanzania) its natural geographical range. We hypothesized that the availability of hard substrate and the amount of wave exposure would explain distribution patterns, and that higher abundance of herbivorous fishes in Tanzania would exert stronger top–down control than in Hawai’i. To address these hypotheses, we surveyed E. denticulatum in sites subjected to different environmental conditions and used generalized linear mixed models (GLMM) to identify predictors of E. denticulatum presence. We also estimated grazing intensity on E. denticulatum by surveying the type and the amount of grazing scars. Finally, we used molecular tools to distinguish between indigenous and non-indigenous strains of E. denticulatum on Mafia Island. In Kane’ohe Bay, the likelihood of finding E. denticulatum increased with wave exposure, whereas on Mafia Island, the likelihood increased with cover of coral rubble, and decreased with distance from areas of introduction (AOI), but this decrease was less pronounced in the presence of coral rubble. Grazing intensity was higher in Kane’ohe Bay than on Mafia Island. However, we still suggest that efforts to reduce non-indigenous E. denticulatum should include protection of important herbivores in both sites because of the high levels of grazing close to AOI. Moreover, we recommend that areas with hard substrate and high structural complexity should be avoided when farming non-indigenous strains of E. denticulatum.

Factors influencing the abundance patterns of reef fish functional guilds in two coastal bays, Philippines

Reef fish occupy numerous functional groups and play integral roles in maintaining the health of coral reef ecosystems. However, the management and conservation of these fish groups, and thus coral reefs, are hindered by a paucity of information regarding their spatial distribution patterns and the environmental drivers behind these patterns in the Philippines. Therefore, this study quantified the spatial abundance patterns of selected functional fish groups around two coastal bays in the Philippines, and determined which factors influenced these patterns on both small, localised and larger regional scales. A modified Reef Check methodology was utilised to determine the abundance of fish groups and the substrate composition for 15 coral reefs situated in five delineated regions. The abundance of herbivorous, coralivorous, and top predatory fishes were highly variable, both within and between reefs. Significant differences in fish group abundance were found at the reef, but not at the regional level. Commercially important fish groups (Scaridae, Lutjanidae, and Epinephelinae) were dominated by small size classes (less than 20 cm total length). Sites were also found to be variable in their substrate composition and subsistence fishing effort. Generalised Linear Mixed Models highlighted that localised influences of fishing and hard coral cover, rather than larger-scale regional influences, were the most influential on the abundance patterns of herbivorous, coralivorous and top predatory fish groups. This may suggest that the current management approach of localised small-scale marine protected areas (MPAs) may benefit some of these fish communities. However, top predatory fish likely display far-reaching movement patterns that are not encompassed by these small MPAs, and further management efforts are recommended.

Dynamic model; the effects of eutrophication and sedimentation on the degradation of Coral Reefs in Spermonde Archipelago, Indonesia

Coral reef condition is influenced by many physical, biological, and anthropogenic processes. This research was designed to build a model between nutrient enrichment, sedimentation, and the abundance of herbivorous fish on macroalgae and coral reef coverage within the context of coral reef degradation. The research was conducted in the Spermonde Archipelago. The method used was the field survey method. The data were analyzed by using modeling instrument techniques. The results show that if there is no control over nutrient supply and sedimentation and efforts to increase the density of herbivorous fish, then the condition of coral reefs in Spermonde Archipelago is threatened with severe damage. The condition of coral reefs can be improved by decreasing nutrient supply and sedimentation of 6% each and increasing the herbivorous fish population by 5%.

Does temperature constrain diet choice in a marine herbivorous fish?

The temperature constraint hypothesis (TCH) states that low water temperatures constrain the efficiency of algal digestion in fishes to an extent that limits the viability of herbivory. It is a widely cited explanation for the decline in diversity and abundance of marine herbivorous fishes at high latitudes. A key prediction of this hypothesis is that temperature-related physiological constraints may be ameliorated in free-living herbivores by a shift from herbivory to omnivory. We investigated this prediction by examining the diet of the primarily herbivorous marine fish Odax pullus (Labridae) at multiple locations spanning a gradient of 10° latitude and encompassing a change in median annual sea surface temperature of 5–7 °C. Foregut content and stable isotope analyses were used to compare diet across locations and results were evaluated against the prediction that a latitudinal temperature constraint on herbivory would result in significant variation in the composition of adult diets or the timing of an ontogenetic switch from omnivory to herbivory at colder, higher latitudes. We found that neither the proportion of animal material consumed nor ontogenetic changes in diet varied across the distributional range of this species in a manner consistent with the predictions of the TCH. This study demonstrates that water temperature does not constrain herbivory in a marine ectothermic herbivore and thus challenges a widely cited hypothesis.

Habitat zonation on coral reefs: Structural complexity, nutritional resources and herbivorous fish distributions.

Distinct zonation of community assemblages among habitats is a ubiquitous feature of coral reefs. The distribution of roving herbivorous fishes (parrotfishes, surgeonfishes and rabbitfishes) is a particularly clear example, with the abundance of these fishes generally peaking in shallow-water, high-energy habitats, regardless of the biogeographic realm. Yet, our understanding of the factors which structure this habitat partitioning, especially with regards to different facets of structural complexity and nutritional resource availability, is limited. To address this issue, we used three-dimensional photogrammetry and structure-from-motion technologies to describe five components of structural complexity (rugosity, coral cover, verticality, refuge density and field-of-view) and nutritional resource availability (grazing surface area) among habitats and considered how these factors are related to herbivorous fish distributions. All complexity metrics (including coral cover) were highest on the slope and crest. Nutritional resource availability differed from this general pattern and peaked on the outer-flat. Unexpectedly, when compared to the distribution of herbivorous fishes, none of the complexity metrics had a marked influence in the models. However, grazing surface area was a strong predictor of both the abundance and biomass of herbivorous fishes. The strong relationship between grazing surface area and herbivorous fish distributions indicates that nutritional resource availability may be one of the primary factors driving the distribution of roving herbivorous fishes. The lack of a relationship between complexity and herbivorous fishes, and a strong affinity of herbivorous fishes for low-complexity, algal turf-dominated outer-flat habitats, offers some cautious optimism that herbivory may be sustained on future, low-complexity, algal turf-dominated reef configurations.

Early recovery dynamics of turbid coral reefs after recurring bleaching events

The worlds’ coral reefs are declining due to the combined effects of natural disturbances and anthropogenic pressures including thermal coral bleaching associated with global climate change. Nearshore corals are receiving increased anthropogenic stress from coastal development and nutrient run-off. Considering forecast increases in global temperatures, greater understanding of drivers of recovery on nearshore coral reefs following widespread bleaching events is required to inform management of local stressors. The west Pilbara coral reefs, with cross-shelf turbidity gradients coupled with a large nearby dredging program and recent history of repeated coral bleaching due to heat stress, represent an opportune location to study recovery from multiple disturbances. Mean coral cover at west Pilbara reefs was monitored from 2009 to 2018 and declined from 45% in 2009 to 5% in 2014 following three heat waves. Recruitment and juvenile abundance of corals were monitored from 2014 to 2018 and were combined with biological and physical data to identify which variables enhanced or hindered early-stage coral recovery of all hard corals and separately for the acroporids, the genera principally responsible for recovery in the short-term (<7 years). From 2014 to 2018, coral cover increased from 5 to 10% but recovery varied widely among sites (0–13%). Hard coral cover typically recovered most at shallower sites that had higher abundance of herbivorous fish, less macroalgae, and lower turbidity. Similarly, acroporid corals recovered most at sites with lower turbidity and macroalgal cover. Juvenile acroporid densities were a good indicator of recovery at least two years after they were recorded. However, recruitment to settlement tiles was not a good predictor of total coral or acroporid recovery. This study shows that coral recovery can be slower in areas of high turbidity and the rate may be reduced by local pressures, such as dredging. Management should focus on improving or maintaining local water quality to increase the likelihood of coral recovery under climate stress. Further, in turbid environments, juvenile coral density predicts early coral recovery better than recruits on tiles and may be a more cost-effective technique for monitoring recovery potential.

Case-control design identifies ecological drivers of endemic coral diseases

Endemic disease transmission is an important ecological process that is challenging to study because of low occurrence rates. Here, we investigate the ecological drivers of two coral diseases–growth anomalies and tissue loss–affecting five coral species. We first show that a statistical framework called the case-control study design, commonly used in epidemiology but rarely applied to ecology, provided high predictive accuracy (67–82%) and disease detection rates (60–83%) compared with a traditional statistical approach that yielded high accuracy (98–100%) but low disease detection rates (0–17%). Using this framework, we found evidence that 1) larger corals have higher disease risk; 2) shallow reefs with low herbivorous fish abundance, limited water motion, and located adjacent to watersheds with high fertilizer and pesticide runoff promote low levels of growth anomalies, a chronic coral disease; and 3) wave exposure, stream exposure, depth, and low thermal stress are associated with tissue loss disease risk during interepidemic periods. Variation in risk factors across host-disease pairs suggests that either different pathogens cause the same gross lesions in different species or that the same disease may arise in different species under different ecological conditions.