Reef fish community structure on coastal islands of the southeastern Brazil: the influence of exposure and benthic cover

Patterns of community structure in the marine environment are strongly influenced by population relationships to biotic and physical gradients. The aim of this work is to explore the relationships of tropical rocky reef fish assemblages to wave exposure and benthic coverage in a gradient of distance from the coast. The study was conducted on the Guarapari Islands, southeastern Brazilian coast. Fish were sampled by underwater visual census (166 transects) and benthic cover was estimated with quadrats (223 replicates). Two main kinds of habitats were found to be derived from the close interrelation between exposure and benthic coverage: (1) exposed areas subjected to major hydrodynamic forcing, and (2) sheltered or moderately exposed areas. The first group is associated with mid-water schooling species like planktivorous labrids and Chromis, piscivorous Caranx, as well as gregarious omnivores like Abudefduf and Diplodus. In terms of benthic composition, macroalgae and encrusting calcareous algae prevail in this high-energy habitat. The second group is characterized by site-attached and reef associated species like territorial pomacentrids, invertebrate feeders such as Halichoeres poeyi and Chaetodon striatus, and small cryptobenthic fishes (e.g. blenniids and labrisomids). Turf algae, zoanthids and massive corals dominate this environment. Environmental plasticity is also common with some genera showing high abundances in all habitats (e.g. Holocentrus, Haemulon, Acanthurus). Examples of the coupling of food availability and fish abundance were found. Planktivores, territorial herbivores, macroalgae browsers and spongivores were positively related with the abundance of their preferred food items along the exposure gradient. Within-family analyses of Pomacentridae and Labridae showed that niche partitioning is likely occurring and seems to be mediated by swimming ‘ability’ and associated feeding performance.     

Reef habitats and associated sessile-benthic and fish assemblages across a euphotic–mesophotic depth gradient in Isla Desecheo, Puerto Rico

Quantitative surveys of sessile benthos and fish populations associated with reef habitats across a 15–50 m depth gradient were performed by direct diver observations using rebreathers at Isla Desecheo, Puerto Rico. Statistically significant differences between depths were found for total live coral, total coral species, total benthic algae, total sponges and abiotic cover. Live coral cover was higher at the mid-shelf (20 m) and shelf-edge (25 m) stations, whereas benthic algae and sponges were the dominant sessile-benthic assemblage at mesophotic stations below 25 m. Marked shifts in the community structure of corals and benthic algae were observed across the depth gradient. A total of 119 diurnal, non-cryptic fish species were observed across the depth gradient, including 80 species distributed among 7,841 individuals counted within belt-transects. Fish species richness was positively correlated with live coral cover. However, the relationship between total fish abundance and live coral was weak. Abundance of several numerically dominant fish species varied independently from live coral cover and appeared to be more influenced by depth and/or habitat type. Statistically significant differences in the rank order of abundance of fish species at euphotic vs mesophotic stations were detected. A small assemblage of reef fishes that included the cherubfish, Centropyge argi, sunshine chromis, Chromis insolata, greenblotch parrotfish, Sparisoma atomarium, yellowcheek wrasse, Halichoeres cyanocephalus, sargassum triggerfish, Xanthichthys ringens, and the longsnout butterflyfish, Chaetodon aculeatus was most abundant or only present from stations deeper than 30 m, and thus appear to be indicator species of mesophotic habitats.     

Seasonal monitoring of coral–algae interactions in fringing reefs of the Gulf of Aqaba, Northern Red Sea

This paper presents seasonal in situ monitoring data on benthic coverage and coral–algae interactions in high-latitude fringing reefs of the Northern Red Sea over a period of 19 months. More than 30% of all hermatypic corals were involved in interaction with benthic reef algae during winter compared to 17% during summer, but significant correlation between the occurrence of coral–algae interactions and monitored environmental factors such as temperature and inorganic nutrient availability was not detected. Between 5 and 10-m water depth, the macroalgae Caulerpa serrulata, Peyssonnelia capensis and filamentous turf algae represented almost 100% of the benthic algae involved in interaction with corals. Turf algae were most frequently (between 77 and 90% of all interactions) involved in interactions with hermatypic corals and caused most tissue damage to them. Maximum coral tissue loss of 0.75% day⁻¹ was observed for Acropora-turf algae interaction during fall, while an equilibrium between both groups of organisms appeared during summer. Slow-growing massive corals were more resistant against negative algal influence than fast-growing branching corals. Branching corals of the genus Acropora partly exhibited a newly observed phenotypic plasticity mechanism, by development of a bulge towards the competing organism, when in interaction with algae. These findings may contribute to understand the dynamics of phase shifts in coral reefs by providing seasonally resolved in situ monitoring data on the abundance and the competitive dynamic of coral–algae interactions.     

Influence of Resource Availability on the Foraging Strategies of the Triangle Butterflyfish Chaetodon triangulum in the Maldives

Obligate coral feeders such as many members of the Chaetodontidae family (also known as butterflyfish) often show strong preferences for particular coral species. This is thought to have evolved through natural selection as an energy-maximising strategy. Although some species remain as highly specialised feeders throughout their lifetime, many corallivores show a degree of dietary versatility when food abundance is limited; a strategy described by the optimal foraging theory. This study aimed to examine if, within-reef differences in the feeding regime and territory size of the Triangle Butterflyfish Chaetodon triangulum occurred, as a function of resource availability. Results showed that the dietary specialisation of C. triangulum was significant in both areas of low and high coral cover (χL2² = 2.52 x 102, P<0.001 and χL2² = 3.78 x 102, P<0.001 respectively). Resource selection functions (RSFs), calculated for the two main sites of contrasting coral assemblage, showed that in the resource-rich environments, only two Genera (Acropora and Pocillopora) were preferentially selected for, with the majority of other corals being actively ‘avoided’. Conversely, in territories of lower coral coverage, C. triangulum was being less selective in its prey choice and consuming corals in a more even distribution with respect to their availability. Interestingly, coral cover appeared to show no significant effect on feeding rate, however it was a primary determinant of territory size. The findings of the study agree with the predictions of the optimal foraging theory, in that where food supply is scarce, dietary specialisation is minimised and territory size increased. This results in maximising energy intake. This study represents the first scientific evidence that C. triangulum is an obligate corallivore and, as with many other butterflyfish, is therefore dependent on healthy scleractinian corals for survival.     

Recovery without resilience: persistent disturbance and long-term shifts in the structure of fish and coral communities at Tiahura Reef, Moorea

Disturbances have a critical effect on the structure of natural communities. In this study long-term changes were examined in the reef community at Tiahura Reef, on the northern coast of Moorea, which had been subject to many and varied disturbances over the last 25 years. Tiahura Reef was subject to an outbreak of crown-of-thorns starfish (Acanthaster planci) in 1980–1981, causing significant declines in the abundance of scleractinian corals and butterflyfishes. By 2003, the abundance of corals and butterflyfishes had returned to former levels, but despite this apparent recovery, the species composition of coral communities and butterflyfish assemblages was very different from those recorded in 1979. Ongoing disturbances (including further outbreaks of crown-of-thorns starfish, cyclones, and coral bleaching events) appear to have prevented recovery of many important coral species (notably, Acropora spp.), which has had subsequent effects on the community structure of coral-feeding butterflyfishes. This study shows that recurrent disturbances may have persistent effects on the structure and dynamics of natural communities.     

Influence of dietary specialization and resource availability on geographical variation in abundance of butterflyfish

Empirical evidence indicates that both niche breadth and resource availability are key drivers of a species' local abundance patterns. However, most studies have considered the influence of either niche breath or resource availability in isolation, while it is the interactive effects that are likely to influence local abundance. We examined geographic variation in the feeding ecology and distribution of coral-feeding butterflyfish to determine the influence of dietary specialization and dietary resource availability on their local abundance. Dietary composition and abundance of five butterflyfish and coral dietary resource availability were determined at 45 sites across five locations (Lizard Island and Heron Island, Great Barrier Reef; Kimbe Bay, Papua New Guinea; Noumea, New Caledonia; and Moorea, French Polynesia). Multiple regression models using variables representative of total dietary resource availability, availability of specific dietary resources, and interspecific competition were used to determine the best predictors of local abundance across all sites and locations for each species. Factors influencing local abundance varied between butterflyfish with specialized and generalized diets. Dietary resource availability had the strongest influence on the abundance of Chaetodon trifascialis-the most specialized species. Local abundance of C. trifascialis was best predicted by availability of the Acropora corals that it preferentially feeds on. In contrast, abundance of generalist butterflyfish was poorly described by variation in availability of specific resources. Rather, indices of total dietary resource availability best predicted their abundance. Overall, multiple regression models only explained a small proportion of the variation in local abundance for all five species. Despite their relatively specialized diets, dietary resource availability has limited influence on the local abundance of butterflyfish. Only the most specialized species appear to be consistently limited by prey availability. Local and total abundance of species are influenced by a wide range of different factors and there is definite need to conduct independent species assessments.     

Disturbance and the structure of coral reef fish communities on the reef slope

Three levels of physical disturbance were applied to corals in permanent 10x10 m quadrats along a section of fringing reef at Lizard Island on the Great Barrier Reef to investigate the response of fish assemblages. Tabular and corymbose corals were overturned and left in situ, reducing total hard coral cover from ˜55% to ˜47%, ˜43%, and ˜34%. Despite pre-existing associations with benthic cover, all fish groups examined (pomacentrids, labrids, chaetodontids, and acanthurids) were resistent to benthic disturbances at the level and scale at which they were applied. Partial Mantel's tests, in combination with partial Canonical Correspondence Analysis enabled spatial and temporal variation to be factored out from experimental effects. Most of the variation in the fish community could be assigned to spatio-temporal variables, indicating that spatial structure over the reef landscape may moderate localised disturbance effects. This study indicates that coral reef fish assemblages may be more resistant to disturbance than many correlative studies would suggest, and highlights a need for further information on levels and scales of natural habitat disturbance in order to apply a structured approach to the experimental investigation of the importance of habitat in structuring coral-reef fish assemblages.     

Abundance,diversity, and feeding behavior of coral reef butterflyfishes at Lord Howe Island

Endemic species are assumed to have a high risk of extinction because their restricted geographic range is often associated with low abundance and high ecological specialization. This study examines the abundance of Chaetodon butterflyfishes at Lord Howe Island in the south‐west Pacific, and compares interspecific differences in local abundance to the feeding behavior and geographic range of these species. Contrary to expected correlations between abundance and geographic range, the single most abundant species of butterflyfish was Chaetodon tricinctus, which is endemic to Lord Howe Island and adjacent reefs; densities of C. tricinctus (14.1 ± 2.1 SE fish per 200m²) were >3 times higher than the next most abundant butterflyfish (Chaetodon melannotus), and even more abundant than many other geographically widespread species. Dietary breadth for the five dominant butterflyfishes at Lord Howe Island was weakly and generally negative correlated with abundance. The endemic C. tricinctus was a distinct outlier in this relationship, though our extensive feeding observations suggest some issues with the measurements of dietary breadth for this species. Field observations revealed that all bites taken on benthic substrates by C. tricinctus were from scleractinian corals, but adults rarely, if ever, took bites from the benthos, suggesting that they may be feeding nocturnally and/or using mid‐water prey, such as plankton. Alternatively, the energetic demands of C. tricinctus may be fundamentally different to other coral‐feeding butterflyfishes. Neither dietary specialization nor geographic range accounts for interspecific variation in abundance of coral reef butterflyfishes at Lord Howe Island, while much more work on the foraging behavior and population dynamics of C. tricinctus will be required to understand its’ abundance at this location.     

The influence of coral reef benthic condition on associated fish assemblages

Accumulative disturbances can erode a coral reef's resilience, often leading to replacement of scleractinian corals by macroalgae or other non-coral organisms. These degraded reef systems have been mostly described based on changes in the composition of the reef benthos, and there is little understanding of how such changes are influenced by, and in turn influence, other components of the reef ecosystem. This study investigated the spatial variation in benthic communities on fringing reefs around the inner Seychelles islands. Specifically, relationships between benthic composition and the underlying substrata, as well as the associated fish assemblages were assessed. High variability in benthic composition was found among reefs, with a gradient from high coral cover (up to 58%) and high structural complexity to high macroalgae cover (up to 95%) and low structural complexity at the extremes. This gradient was associated with declining species richness of fishes, reduced diversity of fish functional groups, and lower abundance of corallivorous fishes. There were no reciprocal increases in herbivorous fish abundances, and relationships with other fish functional groups and total fish abundance were weak. Reefs grouping at the extremes of complex coral habitats or low-complexity macroalgal habitats displayed markedly different fish communities, with only two species of benthic invertebrate feeding fishes in greater abundance in the macroalgal habitat. These results have negative implications for the continuation of many coral reef ecosystem processes and services if more reefs shift to extreme degraded conditions dominated by macroalgae.     

Organic Matter Degradation Drives Benthic Cyanobacterial Mat Abundance on Caribbean Coral Reefs

Benthic cyanobacterial mats (BCMs) are impacting coral reefs worldwide. However, the factors and mechanisms driving their proliferation are unclear. We conducted a multi-year survey around the Caribbean island of Curaçao, which revealed highest BCM abundance on sheltered reefs close to urbanised areas. Reefs with high BCM abundance were also characterised by high benthic cover of macroalgae and low cover of corals. Nutrient concentrations in the water-column were consistently low, but markedly increased just above substrata (both sandy and hard) covered with BCMs. This was true for sites with both high and low BCM coverage, suggesting that BCM growth is stimulated by a localised, substrate-linked release of nutrients from the microbial degradation of organic matter. This hypothesis was supported by a higher organic content in sediments on reefs with high BCM coverage, and by an in situ experiment which showed that BCMs grew within days on sediments enriched with organic matter (Spirulina). We propose that nutrient runoff from urbanised areas stimulates phototrophic blooms and enhances organic matter concentrations on the reef. This organic matter is transported by currents and settles on the seabed at sites with low hydrodynamics. Subsequently, nutrients released from the organic matter degradation fuel the growth of BCMs. Improved management of nutrients generated on land should lower organic loading of sediments and other benthos (e.g. turf and macroalgae) to reduce BCM proliferation on coral reefs.     

Microhabitat characteristics of <Emphasis Type="Italic">Stegastes planifrons</Emphasis> and <Emphasis Type="Italic">S. adustus</Emphasis> territories

Stegastes adustus and Stegastes planifrons are two species of damselfishes commonly found in the Caribbean. These territorial fishes have been widely studied due to their major ecological role on coral reef in controlling the growth of macroalgae that compete with corals for space and, inversely, on their deleterious role in destroying coral tissues to impulse the development of algae. However, few studies were conducted on the biotic and abiotic components of their territories. In the present study, territory size and surfaces of benthic components (macroalgae, algal turf, massive corals, branching corals, Milleporidae, sponges, sand and rubbles) were estimated for the two species at two contrasted sites. At Ilet Pigeon site (IP), the two damselfishes were found at different depth and exhibited different territory sizes. S. adustus defended a larger territory characterized by massive corals, sand and Milleporidae, while S. planifrons territories were smaller, deeper and characterized by branching corals, sponges and rubble. At Passe-à-Colas site (PC), the two fish species coexisted in the same depth range and defended territories of similar size. Their territories presented higher proportions of macroalgae, but smaller surfaces of Milleporidae than at IP. At PC, the main difference between the two species was a higher surface of massive corals inside S. planifrons territories than S. adustus territories. Differences in microhabitat characteristics between the two Stegastes seemed mostly site related. This resulted from the high plasticity of two species, allowing them to persist on Caribbean coral reefs after the decline of most branching acroporids, their former favorite habitats.     

Effects of different disturbance types on butterflyfish communities of Australia’s Great Barrier Reef

The effects of disturbances on coral reef fishes have been extensively documented but most studies have relied on opportunistic sampling following single events. Few studies have the spatial and temporal extent to directly compare the effects of multiple disturbances over a large geographic scale. Here, benthic communities and butterflyfishes on 47 reefs of the Great Barrier Reef were surveyed annually to examine their responses to physical disturbances (cyclones and storms) and/or biological disturbances (bleaching, outbreaks of crown-of-thorns starfish and white syndrome disease). The effects on benthic and butterflyfish communities varied among reefs depending on the structure and geographical setting of each community, on the size and type of disturbance, and on the disturbance history of that reef. There was considerable variability in the response of butterflyfishes to different disturbances: physical disturbances (occurring with or without biological disturbances) produced substantial declines in abundance, whilst biological disturbances occurring on their own did not. Butterflyfishes with the narrowest feeding preferences, such as obligate corallivores, were always the species most affected. The response of generalist feeders varied with the extent of damage. Wholesale changes to the butterflyfish community were only recorded where structural complexity of reefs was drastically reduced. The observed effects of disturbances on butterflyfishes coupled with predictions of increased frequency and intensity of disturbances sound a dire warning for the future of butterflyfish communities in particular and reef fish communities in general.     

Spatial dynamics of benthic competition on coral reefs

The community structure of sedentary organisms is largely controlled by the outcome of direct competition for space. Understanding factors defining competitive outcomes among neighbors is thus critical for predicting large-scale changes, such as transitions to alternate states within coral reefs. Using a spatially explicit model, we explored the importance of variation in two spatial properties in benthic dynamics on coral reefs: (1) patterns of herbivory are spatially distinct between fishes and sea urchins and (2) there is wide variation in the areal extent into which different coral species can expand. We reveal that the size-specific, competitive asymmetry of corals versus fleshy algae highlights the significance of spatial patterning of herbivory and of coral growth. Spatial dynamics that alter the demographic importance of coral recruitment and maturation have profound effects on the emergent structure of the reef benthic community. Spatially constrained herbivory (as by sea urchins) is more effective than spatially unconstrained herbivory (as by many fish) at opening space for the time needed for corals to settle and to recruit to the adult population. Further, spatially unconstrained coral growth (as by many branching coral species) reduces the number of recruitment events needed to fill a habitat with coral relative to more spatially constrained growth (as by many massive species). Our model predicts that widespread mortality of branching corals (e.g., Acropora spp) and herbivorous sea urchins (particularly Diadema antillarum) in the Caribbean has greatly reduced the potential for restoration across the region.     

Similar regional effects among local habitats on the structure of tropical reef fish and coral communities

Aim We examined data on corals and reef fishes to determine how particular local habitat types contribute to variation in community structure across regions covering gradients in species richness and how consistent this was over time. Location Great Barrier Reef (GBR), Australia. Methods We compared large‐scale (1300 km), long‐term (11 years) data on fishes and corals that were collected annually at fixed sites in three habitats (inshore, mid‐shelf and outer‐shelf reefs) and six regions (latitudinal sectors) along a gradient of regional species richness in both communities. We used canonical approaches to partition variation in community structure (sites × species abundance data matrices) into components associated with habitat, region and time and Procrustes analyses to assess the degree of concordance between coral and fish community structure. Results Remarkably similar patterns emerged for both fish and coral communities occupying the same sites. Reefs that had similar coral communities also had similar fish communities. The fraction of the community data that could be explained by regional effects, independent of pure habitat effects, was similar in both fish (33%) and coral (36.9%) communities. Pure habitat effects were slightly greater in the fish (31.3%) than in the coral (20.1%) community. Time explained relatively little variation (fish = 7.9%, corals = 9.6%) compared with these two spatial factors. Conclusions Our results indicate either that fish and coral communities were structured in similar ways by processes associated with region, habitat and time, or that the variation in fish community structure tracked variation associated with the coral communities at these sites and thereby reflects an indirect link between the environment and the structure of fish communities mediated by corals. Irrespective of the causes of such commonality, we demonstrate that community structure, not just species richness, can be related to both habitat differences and regional setting simultaneously.     

Space partitioning by stony corals soft corals and benthic algae on the coral reefs of the northern Gulf of Eilat (Red Sea)

The major faunistic and floristic components occupying space on the coral reefs of the northern Gulf of Eilat (Red Sea) are stony corals, soft corals and benthic algae. The percent living coverage of the three components and the relative abundance of the different species of each component were studied by line transects, on the reef flats and the upper forereef zones of nine localities. A wider and higher range of living coverage values of stony corals were recorded at the upper fore-reef zones (18.30–49.09%) compared with the reef flats (5.50–31.66%) at the different stations. The most abundant stony corals on the reef flats areCyphastrea microphthalma, Stylophora pistillata, Favia favus, Porites lutea, Platygyra lamellina and the hydrozoanMillepora dichotoma. The fire coralM. dichotoma dominates the upper fore-reef zone in most of the stations. The average percent living coverage of soft corals on the reef flats ranged between 0.20 and 17.06%, and on the upper fore-reef zones between 1.68 and 15.13%. Seventy percent of the total living coverage of the soft coral community is contributed by 2 to 3 species. They tend to form large monospecific carpets, such as those composed ofSinularia sp.,Sarcophyton glaucum andLobophytum pauciflorum. The common benthic algae on the coral reef studied occur as turfs or macroscopic noncalcareous algae. They play a significant role in occupying space, especially on the reef flats. The most abundant algae recorded in all localities are the turfsSphacelaria tribuloides, Jania sp. and the macroscopic non-calcareous algaeTurbinaria elatensis andColpomenia sinuosa. Comparison between reef flats and upper fore-reef zones, in terms of average living cover of stony corals, shows that the variation among the reef flats is grater than the variation among the upper fore-reef zones. However, there is no significant variation in the average living coverage of soft corals between these two zones. Annual living-coverage values of algae on the reef flats are significantly higher than those of the upper fore-reef zones. Extremely low tides occurring periodically but unpredictably at Eilat cause mass mortality of the benthic communities on the reef flats reopening new spaces for settlement. The coexistence of stony corals, soft corals and algae on the reef ecosystem is due to different biological properties of each component. Opportunistic life histories of certain stony corals and most algae enable quick colonization of newly opened spaces. Lack of predators, high tolerance against abiotic factors and ability to form large aggregates of colonies are suggested as possible factors supporting the existence of soft corals in shallow water. Biological factors such as competition, predation and grazing pressure play an increasingly important role in controlling space utilization by the components studied with the advancement of succession.     

Implications of feeding specialization on the recruitment processes and community structure of butterflyfishes

Synopsis When settling on coral reefs, fish larvae generally change from zooplanktivory to diverse forms of benthic feeding. Whereas food has not been reported to directly influence settlement, it is hypothesized that food resource might play a major role in the recruitment processes of butterflyfishes. Benthic feeding was found to occur immediatly after settlement, and was related to the degree of specialization of adult diets. Among obligate coral feeders scleractinian polyps were the exclusive diet of new recruits. In non-obligate corallivorous chaetodontids tentacles of sedentarian polychaetes were the preferred prey of juveniles for all the species studied, and represented on average 36.2% of their prey by weight. They formed a transitional food resource for these species which mainly fed on scleratinian polyps when adults (51.6% by weight). Among the chaetodontids studies, some recruited within adult home sites, whereas others exhibited size-specific distributions. The different patterns observed were not closely related to food specialization of the adults. The importance of food resources to the community structure of butterflyfishes on coral reefs is discussed.     

Microbial to reef scale interactions between the reef-building coral Montastraea annularis and benthic algae

Competition between reef-building corals and benthic algae is of key importance for reef dynamics. These interactions occur on many spatial scales, ranging from chemical to regional. Using microprobes, 16S rDNA pyrosequencing and underwater surveys, we examined the interactions between the reef-building coral Montastraea annularis and four types of benthic algae. The macroalgae Dictyota bartayresiana and Halimeda opuntia, as well as a mixed consortium of turf algae, caused hypoxia on the adjacent coral tissue. Turf algae were also associated with major shifts in the bacterial communities at the interaction zones, including more pathogens and virulence genes. In contrast to turf algae, interactions with crustose coralline algae (CCA) and M. annularis did not appear to be antagonistic at any scale. These zones were not hypoxic, the microbes were not pathogen-like and the abundance of coral-CCA interactions was positively correlated with per cent coral cover. We propose a model in which fleshy algae (i.e. some species of turf and fleshy macroalgae) alter benthic competition dynamics by stimulating bacterial respiration and promoting invasion of virulent bacteria on corals. This gives fleshy algae a competitive advantage over corals when human activities, such as overfishing and eutrophication, remove controls on algal abundance. Together, these results demonstrate the intricate connections and mechanisms that structure coral reefs.     

Vertical zonation of megabenthic taxa on a deep photosynthetic reef (50–140 m) in the Au’au Channel,Hawaii

This study surveyed several locations at depths between 50 and 140 m within the Au’au Channel, Hawaii to characterize the deep reef habitat and determine the depth distribution and relative abundance of the dominant, habitat forming megabenthic taxa. In the Au’au Channel, the depth distribution of megabenthic taxa exhibited a pattern of vertical zonation with relatively few taxa dominating each zone. Macroalgae particularly Halimeda spp. and to a lesser extent scleractinian corals Leptoseris spp. were dominant between 50 and 80 m; Leptoseris spp. were dominant between 80 and 90 m as macroalgae decreased in abundance; the invasive octocoral Carijoa riisei was dominant between 90 and 100 m primarily on rugose features; Antipathes spp. and Leptoseris spp. were dominant between 100 and 120 m on exposed fossil reef; and small wire corals were dominant between 120 and 140 m. In general, the percentage of live benthic cover decreased with depth, particularly below 90 m where a large majority of the area was uncolonized, soft substrata. The gradient of downwelling light intensity appears to play a major role in regulating the depth distribution of photosynthetic organisms, skilophilous organisms, and other benthic fauna, which compete for space with dominant photosynthetic species. The depth of the seasonal thermocline also appears to play an important role in limiting the distribution of tropical benthic species.     

Structure-forming corals and sponges and their use as fish habitat in Bering Sea submarine canyons

Continental margins are dynamic, heterogeneous settings that can include canyons, seamounts, and banks. Two of the largest canyons in the world, Zhemchug and Pribilof, cut into the edge of the continental shelf in the southeastern Bering Sea. Here currents and upwelling interact to produce a highly productive area, termed the Green Belt, that supports an abundance of fishes and squids as well as birds and marine mammals. We show that in some areas the floor of these canyons harbors high densities of gorgonian and pennatulacean corals and sponges, likely due to enhanced surface productivity, benthic currents and seafloor topography. Rockfishes, including the commercially important Pacific ocean perch, Sebastes alutus, were associated with corals and sponges as well as with isolated boulders. Sculpins, poachers and pleuronectid flounders were also associated with corals in Pribilof Canyon, where corals were most abundant. Fishes likely use corals and sponges as sources of vertical relief, which may harbor prey as well as provide shelter from predators. Boulders may be equivalent habitat in this regard, but are sparse in the canyons, strongly suggesting that biogenic structure is important fish habitat. Evidence of disturbance to the benthos from fishing activities was observed in these remote canyons. Bottom trawling and other benthic fishing gear has been shown to damage corals and sponges that may be very slow to recover from such disturbance. Regulation of these destructive practices is key to conservation of benthic habitats in these canyons and the ecosystem services they provide.     

Micro-topography mediates interactions between corals,algae, and herbivorous fishes on coral reefs

Processes occurring during the early life stages of corals are important for the replenishment of coral assemblages and the resilience of coral reefs. However, the factors influencing early life stages of corals are not well understood, and the role of micro-topographic complexity for habitat associations of juvenile corals is largely unexplored. This study investigated the microhabitat distribution patterns of early life stages of corals and a potential macroalgal competitor (Turbinaria ornata) across two reef zones (reef crest and outer reef flat) on Lizard Island, Great Barrier Reef. In both reef zones, both corals and T. ornata were significantly more abundant in concealed microhabitats than in semi-concealed or open microhabitats (GLMM: P < 0.001). The prevalence of juvenile corals and T. ornata within concealed environments suggests that they might be effective refuges from grazing by herbivorous fishes. The density of juvenile corals was positively related, and density of T. ornata negatively related to the abundance of two groups of herbivorous fishes, pairing rabbitfishes, and surgeonfishes in the genus Zebrasoma (BEST ENV-BIO: r _s  = 0.72, P < 0.01), which feed in concealed microhabitats. This correlative evidence suggests that crevices may be important for early life stages of both coral and macroalgae, and that a specific suite of crevice-feeding fishes may influence benthic community dynamics in these microhabitats.