Disturbed Coral Reefs Research Articles

The bacterial signature offers vision into the machinery of coral fitness across high-latitude coral reef in the South China Sea.

Coral-bacterial interaction is a major driver in coral acclimatization to the stressful environment. 16S rRNA High-throughput sequencing was used to classify the role of different coral reef compartments; sediment, water, and tissue; in the South China Sea (SCS), as well as different locations in shaping the microbial community. The majority of OTUs significantly shifted at impacted sites and indicated distinction in the relative abundance of bacteria compartment/site-wise. Richness and diversity were higher, and more taxa were enriched in the sediment communities. Proteobacteria dominated sediment samples, while Cyanobacteria dominated water samples. Coral tissue showed a shift among different sites with Proteobacteria remaining the dominant Phylum. Moreover, we report a dominance of Chlorobium genus in the healthy coral tissue sample collected from the severely damaged Site B, suggesting a contribution to tolerance and adaptation to the disturbing environment. Thus, revealing the complex functionally diverse microbial patterns associated with biotic and abiotic disturbed coral reefs will deliver understanding of the symbiotic connections and competitive benefit inside the hosts niche and can reveal a measurable footprint of the environmental impacts on coral ecosystems. We hence, urge scientists to draw more attention towards using coral microbiome as a self-sustaining tool in coral restoration.

Rapid regeneration of Acropora millepora coral recruits after physical damage to the primary polyp

High post-settlement mortality is thought to be a major limiting factor for the recovery of disturbed coral reef populations, as newly settled corals face a range of physical, chemical, and biological interactions that can inhibit their development. During recruitment, physical interactions are common, with recruits settling on loose substrates likely to be abraded during storm events, while incidental grazing and predation on exposed surfaces may also inflict damage. Nevertheless, larvae have been observed to recruit and survive on substrates where physical damage is likely, possibly owing to their regenerative capacity. Here, we present the first visual time-series evidence of recruit regeneration following physical damage. To investigate regeneration of these recruits, we sliced and removed tissue from individual Acropora millepora coral recruits and tracked their recovery through survivorship and linear growth. Coral recruits were very robust to slicing, even if the mouth-stomodeum was damaged, which does not support the previously held view that damage to this area is terminal. While section removal did show some evidence of damage at later stages, recruits were more robust to damage than expected which may assist their survival in dynamic habitats.

Sexual reproduction in the soft coral Lobophytum schoedei in Bolinao‐Anda Reef Complex, Pangasinan, northwestern Philippines

AbstractThe characterization of early life‐history strategies of soft corals is important in understanding population maintenance, replenishment, and recovery in disturbed coral reefs. This study examined the sexual reproduction of the soft coral Lobophytum schoedei in the Bolinao‐Anda Reef Complex (BARC), a degraded reef in northwestern Philippines. Reproductive strategies such as sexuality, sex ratio, fecundity, and reproductive timing were examined. Random colonies of L. schoedei were sampled a few weeks before the predicted time of spawning to assess fecundity (n = 73 colonies), and sexuality and sex ratio (n = 221 colonies). Monthly sampling of tagged colonies of L. schoedei (n = 20) was done over 13 months to determine the reproductive timing through polyp dissection. Peak of annual spawning was inferred based on the presence of large gametes and their absence in the next sampling period. Results showed that L. schoedei is a gonochoric broadcast spawner with 1:1.1 sex ratio. Although oogenesis and spermatogenesis exhibited overlapping cycles, both gametes matured and spawned in April, coinciding with increasing sea surface temperature. Prior to spawning, oocytes and spermaries ranged 300–633 µm and 150–337 µm in diameter, respectively. Mean female fecundity was 6.7 ± 3.9 oocytes per polyp and male fecundity was 39.2 ± 22.5 (±SD) spermaries per polyp. Some of these results, including the low number of oocytes produced by female polyps, may be caused by sexual reproduction in a degraded reef environment. Understanding these reproductive traits may be useful for predicting the resiliency of populations of L. schoedei in response to ongoing and future environmental change.

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.

Patterns of Association between Marine Sponges and the Associated Organisms: Case Study, Losin Island, Pattani, Thailand

Ko Losin, the southernmost offshore islet in the Gulf of Thailand is one of the most naturally, less anthropogenic disturbed coral reefs in Thailand and the home of the major sessile organisms: corals and sponges. This study aims to investigate the natural patterns of association (interactions) between marine sponges and the associated organisms. The types of interaction were classified into 4 categories: Gap, Overgrown, Tissue contact, and Overgrow. The investigation focused on four genera of sponges: Chondrilla, Hyrtios, Cinachyrella, and Xestospongia. Chondrillid sponge showed the high frequency of inhabiting associated organisms. Some hermatypic corals such as Montiporian corals and Porites corals were highly proportioned to the associated organisms. The gap and overgrown interactions were recorded in this study.

Species richness and composition of macroalgal assemblages of a disturbed coral reef in the Gulf of California, Mexico

Abstract:Background and Aims: In September 2001, the coral reef of the San Lorenzo Channel, La Paz Bay, Gulf of California, Mexico, was affected by the stranding of the oil tank vessel “Lázaro Cárdenas II”. Soon afterwards, hurricane “Juliette” hit the area with strong winds and water movement, disturbing the reef again. After that, three zones could be observed in the reef: one directly impacted by the shipwreck, one indirectly impacted by the hurricane, which moved and accumulated the coral debris left by the shipwreck, and the third one, which was not impacted. Later, a monitoring program was established to determine the degree of recovery of macroalgal assemblages in both impacted zones compared with the non-impacted one.Methods: From February 2005 to December 2007, macroalgae were collected seasonally by scuba divers in the three zones. In each zone, three to five thalli of all conspicuous algae, five rocks and five fragments of dead coral covered with macroalgal turfs were collected. Species number and composition of macroalgae assemblages were compared between zones and between years.Key results: A total of 117 species were found, 70 belonged to the phylum Rhodophyta, 25 to Ochrophyta-Phaeophyceae, and 22 to Chlorophyta. Macroalgal species richness and composition of the impacted zones were not different from the control zone, even between years.Conclusions: Macroalgal assemblages in the San Lorenzo Channel coral reef were able to recover, regardless of the modification of the substrate caused by the stranding and the hurricane “Juliette” in 2001. Therefore, it is important to implement monitoring efforts in case of anthropogenic or natural disturbance to document the extension of damage, recovery of the communities, and propose mitigation strategies if necessary.

Marine reserves stabilize fish populations and fisheries yields in disturbed coral reef systems.

Marine reserve networks are increasingly implemented to conserve biodiversity and enhance the persistence and resilience of exploited species and ecosystems. However, the efficacy of marine reserve networks in frequently disturbed systems, such as coral reefs, has rarely been evaluated. Here we analyze a well-mixed larval pool model and a spatially explicit model based on a well-documented coral trout (Plectropomus spp.) metapopulation in the Great Barrier Reef Marine Park, Australia, to determine the effects of marine reserve coverage and placement (in relation to larval connectivity and disturbance heterogeneity) on the temporal stability of fisheries yields and population biomass in environmentally disturbed systems. We show that marine reserves can contribute to stabilizing fishery yield while increasing metapopulation persistence, irrespective of whether reserves enhance or diminish average fishery yields. However, reserve placement and the level of larval connectivity among subpopulations were important factors affecting the stability and sustainability of fisheries and fish metapopulations. Protecting a mix of disturbed and non-disturbed reefs, rather than focusing on the least-disturbed habitats, was the most consistently beneficial approach across a range of dispersal and reserve coverage scenarios. Placing reserves only in non-disturbed areas was the most beneficial for biomass enhancement, but had variable results for fisheries and could potentially destabilize yields in systems with well-mixed larval or those that are moderately fished. We also found that focusing protection on highly disturbed areas could actually increase variability in yields and biomass, especially when degraded reef reserves were distant and poorly connected to the meta-population. Our findings have implications for the design and implementation of reserve networks in the presence of stochastic, patchy environmental disturbances.

Spatial and temporal changes in reef fish assemblages on disturbed coral reefs, north Pacific coast of Costa Rica

AbstractBenthic structure of coral reefs determines the availability of refuges and food sources. Therefore, structural changes caused by natural and anthropogenic disturbances can have negative impacts on reef‐associated communities. During the 1990s, coral reefs from Bahía Culebra were considered among the most diverse ecosystems along the Pacific coast of Costa Rica; however, recently they have undergone severe deterioration as consequence of chronic stressors such as El Niño‐Southern Oscillation and harmful algal blooms. Reef fish populations in this area have also been intensely exploited. This study compared reef fish assemblages during two periods (1995–1996 and 2014–2016), to determine whether they have experienced changes as a result of natural and anthropogenic disturbances. For both periods, benthic composition and reef fish abundance were recorded using underwater visual censuses. Live coral cover (LCC) decreased from 43.09 ± 18.65% in 1995–1996 to 1.25 ± 2.42% in 2014–2016 (U = 36, p < 0.05). Macroalgal cover (%) in 2014–2016 was sixfold higher than mean values reported for the Eastern Tropical Pacific region. Mean (±SD) fish species richness in 1995–1996 (36.67 ± 14.20) was higher than in 2014–2016 (23.00 ± 9.14; U = 20, p < 0.05). Over 40% of reef fish orders observed in 1995–1996 were not detected in the 2014–2016 surveys, including large‐bodied predators. Reduction in abundance of fish predators such as sharks, grunts, and snappers is likely attributed to changes in habitat structure. Herbivorous such as parrotfishes and pufferfishes increased their abundance at sites with low LCC, probably in response to predators decline and increased algal cover. These findings revealed significant degradation and drastic loss of structural complexity in coral reefs from Bahía Culebra, which now are dominated by macroalgae. The large reduction in structural complexity of coral reefs has resulted in the loss of diversity and key ecological roles (e.g., predation and herbivory), thus potentially reducing the resilience of the entire ecosystem.

SPECIES DIVERSITY OF THE EPIBENTHOS IN A HIGHLY DISTURBED CORAL REEF COMMUNITY IN THE PHILIPPINES

Baseline studies on the marine benthic communities around the proposed site of the first nuclear power plant in the Philippines have indicated a highly disturbed coral reef community. The areas studied are all subtidal, mostly starting just below the littoral and having an average depth of five meters. The study consisted in taking a census with SCUBA of the epibiota in quadrats on transects laid out perpendicular to the shoreline. Results of the sampling during the dry season indicate a predominantly algal (Padina) community of low species diversity. Many of the conspicuous components of Philippine coral reefs are either absent or are present only in small numbers, e.g., hard and soft corals, crinoids, tridacnids, and colorful serpulids. Dynamite fishing is no doubt a major factor responsible for the condition of the dead reefs. Weather and erosion of the land areas with the resulting siltation have probably contributed to the poor condition of the reef communities as well.

Coral spawning and spawn-slick observation in the Philippines

Knowledge on coral reproduction has implications for the restoration and recovery of degraded coral communities. Few studies on coral spawning timing and extent of synchrony have been recorded in the most biodiverse and disturbed coral reef ecosystems of the Coral Triangle. In the present study, the reproductive timing in 2015 and 2016 is reported of an Acropora assemblage in Magsaysay reef, Bolinao-Anda Reef Complex, northwestern Philippines. Fertile colonies were present in February and March, with highest abundance 6 days after full moon. All sampled colonies of five Acropora species were fertile on 12 March 2015 and 73–100% of six Acropora species on 29 February 2016. Other species had fewer mature colonies (40 and 33% respectively), suggesting that these may spawn in other times of the year. Synchrony in gamete development and mass spawning were exhibited among species. At least eight Acropora species were observed spawning between 9 to 11 days after full moon in March of 2015 and 2016. Mass spawning resulted in spawn slicks, which were dispersed by the current generated by the ebbing tides and winds. This observation suggests that the Magsaysay reef may be an important source of larvae that may recruit unto nearby reefs, which could potentially initiate recovery of degraded coral communities.

Coral reef destruction of Small island in 44 years and destructive fishing in Spermonde Archipelago, Indonesia

Coral reefs are among the most diverse and threatened ecosystems on the planet. The most commonly stated for developing coral reef remote sensing techniques is to asses and or to monitor the status of these ecosystems. The study site was selected one of small island in inner zone Spermonde archipelago, Indonesia. We used Landsat MSS, Landsat TM, Landsat ETM, and Landsat OLI data to examine changes in the coral reefs of inner zone island in the Spermonde Archipelago from 1972 to 2016. The image processing are gap fills, atmospheric correction, geometric corrections, image composites, water column corrections, unsupervised classifications, and reclassification. Some of component change detection procedure was applied to define change. The results showed significant changes in 44 years. Disturbed coral reefs are typically characterized by loss of coral cover by increase in the abundance of dead corals and rubble. Local factors such as destructive fishing is direct destruction of inner zone island. While the impact of local threats may be reduced through management action, global threats to coral reefs are likely to increase in severity in the coming years.

Assessing the herbivore role of the sea-urchin Echinometra viridis: Keys to determine the structure of communities in disturbed coral reefs

Echinometra viridis previously was considered a cryptic species unable to control the development and growth of macroalgae on coral reefs. Its role as a herbivore was seen as minor compared to other grazers present on the reef. However, the present disturbed state of some reefs has highlighted the role played by this sea-urchin. Combining field data with experiments on the Caribbean coast of Panama, we demonstrate that the current community organization on disturbed coral reefs in the Mesoamerican Caribbean is largely due to the action of E. viridis. It is the most abundant sea-urchin species, together with two others (Diadema antillarum and Echinometra lucunter). Field data also indicate that the relationship between its density and the abundance of macroalgae is stronger and it is more negative in impact than those of the other two. However, the niche this urchin exploits most efficiently is confined to leeward reefs with low levels of sedimentation. Outside these habitats, their populations are not decisive in controlling macroalgal growth. Grazing experiments showed that E. viridis consumes more fresh macroalgae per day and per weight of sea-urchin, and is a more effective grazer than D. antillarum or E. lucunter. E. viridis showed food preferences for early-successional turf macroalgae (Acanthophora spicifera), avoiding the less palatable late-successional and fleshy macroalgae (Lobophora variegata, Halimeda opuntia). However, it becomes a generalist herbivore feeding on all varieties of macroalgae when resources are scarce. H. opuntia is the macroalga that most resists E. viridis activity, which may explain its wide distribution.

El Niño and coral larval dispersal across the eastern Pacific marine barrier.

More than 5,000 km separates the frequently disturbed coral reefs of the Eastern Tropical Pacific (ETP) from western sources of population replenishment. It has been hypothesized that El Niño events facilitate eastward dispersal across this East Pacific Barrier (EPB). Here we present a biophysical coral larval dispersal model driven by 14.5 years of high-resolution surface ocean current data including the extreme 1997–1998 El Niño. We find no eastward cross-EPB connections over this period, which implies that ETP coral populations decimated by the 1998 bleaching event can only have recovered from eastern Pacific sources, in congruence with genetic data. Instead, rare connections between eastern and central Pacific reefs are simulated in a westward direction. Significant complexity and variability in the surface flows transporting larvae mean that generalized upper-ocean circulation patterns are poor descriptors of inter-regional connectivity, complicating the assessment of how climate change will impact coral gene flow Pacific wide.

Non-Random Variability in Functional Composition of Coral Reef Fish Communities along an Environmental Gradient.

Changes in the coral reef complex can affect predator-prey relationships, resource availability and niche utilisation in the associated fish community, which may be reflected in decreased stability of the functional traits present in a community. This is because particular traits may be favoured by a changing environment, or by habitat degradation. Furthermore, other traits can be selected against because degradation can relax the association between fishes and benthic habitat. We characterised six important ecological traits for fish species occurring at seven sites across a disturbed coral reef archipelago in Indonesia, where reefs have been exposed to eutrophication and destructive fishing practices for decades. Functional diversity was assessed using two complementary indices (FRic and RaoQ) and correlated to important environmental factors (live coral cover and rugosity, representing local reef health, and distance from shore, representing a cross-shelf environmental gradient). Indices were examined for both a change in their mean, as well as temporal (short-term; hours) and spatial (cross-shelf) variability, to assess whether fish-habitat association became relaxed along with habitat degradation. Furthermore, variability in individual traits was examined to identify the traits that are most affected by habitat change. Increases in the general reef health indicators, live coral cover and rugosity (correlated with distance from the mainland), were associated with decreases in the variability of functional diversity and with community-level changes in the abundance of several traits (notably home range size, maximum length, microalgae, detritus and small invertebrate feeding and reproductive turnover). A decrease in coral cover increased variability of RaoQ while rugosity and distance both inversely affected variability of FRic; however, averages for these indices did not reveal patterns associated with the environment. These results suggest that increased degradation of coral reefs is associated with increased variability in fish community functional composition resulting from selective impacts on specific traits, thereby affecting the functional response of these communities to increasing perturbations.

Mesophotic depths as refuge areas for fishery-targeted species on coral reefs

Coral reefs are subjected to unprecedented levels of disturbance with population growth and climate change combining to reduce standing coral cover and stocks of reef fishes. Most of the damage is concentrated in shallow waters (<30 m deep) where humans can comfortably operate and where physical disturbances are most disruptive to marine organisms. Yet coral reefs can extend to depths exceeding 100 m, potentially offering refuge from the threats facing shallower reefs. We deployed baited remote underwater stereo-video systems (stereo-BRUVs) at depths of 10–90 m around the southern Mariana Islands to investigate whether fish species targeted by fishing in the shallows may be accruing benefits from being at depth. We show that biomass, abundance and species richness of fishery-targeted species increased from shallow reef areas to a depth of 60 m, whereas at greater depths, a lack of live coral habitat corresponded to lower numbers of fish. The majority of targeted species were found to have distributions that ranged from shallow depths (10 m) to depths of at least 70 m, emphasising that habitat, not depth, is the limiting factor in their vertical distribution. While the gradient of abundance and biomass versus depth was steepest for predatory species, the first species usually targeted by fishing, we also found that fishery-targeted herbivores prevailed in similar biomass and species richness to 60 m. Compared to shallow marine protected areas, there was clearly greater biomass of fishery-targeted species accrued in mesophotic depths. Particularly some species typically harvested by depth-limited fishing methods (e.g., spearfishing), such as the endangered humphead wrasse Cheilinus undulatus, were found in greater abundance on deeper reefs. We conclude that mesophotic depths provide essential fish habitat and refuge for fishery-targeted species, representing crucial zones for fishery management and research into the resilience of disturbed coral reef ecosystems.

Strong genetic structure among coral populations within a conservation priority region, the Bird's Head Seascape (Papua, Indonesia)

Marine Protected Areas (MPAs) are widely considered to be one of the best strategies available for protecting species diversity and ecosystem processes in marine environments. While data on connectivity and genetic structure of marine populations are critical to designing appropriately sized and spaced networks of MPAs, such data are rarely available. This study examines genetic structure in reef-building corals from Papua and West Papua, Indonesia, one of the most biodiverse and least disturbed coral reef regions in the world. We focused on two common reef-building corals, Pocillopora damicornis (Linnaeus 1758) and Seriatopora hystrix (family: Pocilloporidae), from three regions under different management regimes: Teluk Cenderawasih, Raja Ampat, and southwest Papua. Analyses of molecular variance, assignment tests, and genetical bandwidth mapping based on microsatellite variation revealed significant genetic structure in both species, although there were no clear regional filters to gene flow among regions. Overall, P. damicornis populations were less structured (FST = 0.139, p &lt; 0.00001) than S. hystrix (FST = 0.357, p &lt; 0.00001). Despite occurring in one of the most pristine marine habitats in Indonesia, populations of both species showed evidence of recent declines. Furthermore, exclusion of individual populations from connectivity analyses resulted in marked increases in self-recruitment. Maintaining connectivity within and among regions of Eastern Indonesia will require coral conservation on the local scales and regional networks of MPAs.&nbsp

Chemical and Physical Environmental Conditions Underneath Mat- and Canopy-Forming Macroalgae, and Their Effects on Understorey Corals

Disturbed coral reefs are often dominated by dense mat- or canopy-forming assemblages of macroalgae. This study investigated how such dense macroalgal assemblages change the chemical and physical microenvironment for understorey corals, and how the altered environmental conditions affect the physiological performance of corals. Field measurements were conducted on macroalgal-dominated inshore reefs in the Great Barrier Reef in quadrats with macroalgal biomass ranging from 235 to 1029 g DW m−2 dry weight. Underneath mat-forming assemblages, the mean concentration of dissolved oxygen was reduced by 26% and irradiance by 96% compared with conditions above the mat, while concentrations of dissolved organic carbon and soluble reactive phosphorous increased by 26% and 267%, respectively. The difference was significant but less pronounced under canopy-forming assemblages. Dissolved oxygen declined and dissolved inorganic carbon and alkalinity increased with increasing algal biomass underneath mat-forming but not under canopy-forming assemblages. The responses of corals to conditions similar to those found underneath algal assemblages were investigated in an aquarium experiment. Coral nubbins of the species Acropora millepora showed reduced photosynthetic yields and increased RNA/DNA ratios when exposed to conditions simulating those underneath assemblages (pre-incubating seawater with macroalgae, and shading). The magnitude of these stress responses increased with increasing proportion of pre-incubated algal water. Our study shows that mat-forming and, to a lesser extent, canopy-forming macroalgal assemblages alter the physical and chemical microenvironment sufficiently to directly and detrimentally affect the metabolism of corals, potentially impeding reef recovery from algal to coral-dominated states after disturbance. Macroalgal dominance on coral reefs therefore simultaneously represents a consequence and cause of coral reef degradation.

Behaviourally mediated phenotypic selection in a disturbed coral reef environment.

Natural and anthropogenic disturbances are leading to changes in the nature of many habitats globally, and the magnitude and frequency of these perturbations are predicted to increase under climate change. Globally coral reefs are one of the most vulnerable ecosystems to climate change. Fishes often show relatively rapid declines in abundance when corals become stressed and die, but the processes responsible are largely unknown. This study explored the mechanism by which coral bleaching may influence the levels and selective nature of mortality on a juvenile damselfish, Pomacentrus amboinensis, which associates with hard coral. Recently settled fish had a low propensity to migrate small distances (40 cm) between habitat patches, even when densities were elevated to their natural maximum. Intraspecific interactions and space use differ among three habitats: live hard coral, bleached coral and dead algal-covered coral. Large fish pushed smaller fish further from the shelter of bleached and dead coral thereby exposing smaller fish to higher mortality than experienced on healthy coral. Small recruits suffered higher mortality than large recruits on bleached and dead coral. Mortality was not size selective on live coral. Survival was 3 times as high on live coral as on either bleached or dead coral. Subtle behavioural interactions between fish and their habitats influence the fundamental link between life history stages, the distribution of phenotypic traits in the local population and potentially the evolution of life history strategies.

Maintenance of fish diversity on disturbed coral reefs

Habitat perturbations play a major role in shaping community structure; however, the elements of disturbance-related habitat change that affect diversity are not always apparent. This study examined the effects of habitat disturbances on species richness of coral reef fish assemblages using annual surveys of habitat and 210 fish species from 10 reefs on the Great Barrier Reef (GBR). Over a period of 11 years, major disturbances, including localised outbreaks of crown-of-thorns sea star (Acanthaster planci), severe storms or coral bleaching, resulted in coral decline of 46–96% in all the 10 reefs. Despite declines in coral cover, structural complexity of the reef framework was retained on five and species richness of coral reef fishes maintained on nine of the disturbed reefs. Extensive loss of coral resulted in localised declines of highly specialised coral-dependent species, but this loss of diversity was more than compensated for by increases in the number of species that feed on the epilithic algal matrix (EAM). A unimodal relationship between areal coral cover and species richness indicated species richness was greatest at approximately 20% coral cover declining by 3–4 species (6–8% of average richness) at higher and lower coral cover. Results revealed that declines in coral cover on reefs may have limited short-term impact on the diversity of coral reef fishes, though there may be fundamental changes in the community structure of fishes.

Environmental factors influencing urchin spatial distributions on disturbed coral reefs (New Caledonia, South Pacific)

Few works have examined the relative contributions of habitat variables to the distribution of coral reef urchins. In the present study, the spatial distribution of two common urchin species ( Diadema setosum and Echinometra mathaei) was studied in the fringing reefs of two urban bays in New Caledonia (South Pacific). Urchins were surveyed at 105 stations with contrasted habitat structure/anthropic disturbance levels; 32 environmental variables (water/sediment characteristics, reef structuring species) were considered. Moderate densities were generally observed at station scale (mean 0.5 individuals m − 2 ). The combination of univariate and multivariate techniques highlighted patchy distributions for Diadema as well as Echinometra, with distinct species/habitat associations; environmental gradients occurring within the bays did not seem to influence the species patterns. For Diadema, the spatial variability was better explained by sediment type than by biotic cover; increasing densities occurred across habitats with larger sediment sizes and decreasing coral complexity/macrophytes cover. In contrast, the distribution of E. mathaei exhibited weak relationships with habitat variables. In coral reefs, small-scale heterogeneity may thus be responsible for most of urchins spatial variability.