Non‐reef habitats in a tropical seascape affect density and biomass of fishes on coral reefs

Nonreef habitats such as mangroves, seagrass, and macroalgal beds are important for foraging, spawning, and as nursery habitat for some coral reef fishes. The spatial configuration of nonreef habitats adjacent to coral reefs can therefore have a substantial influence on the distribution and composition of reef fish. We investigate how different habitats in a tropical seascape in the Philippines influence the presence, density, and biomass of coral reef fishes to understand the relative importance of different habitats across various spatial scales. A detailed seascape map generated from satellite imagery was combined with field surveys of fish and benthic habitat on coral reefs. We then compared the relative importance of local reef (within coral reef) and adjacent habitat (habitats in the surrounding seascape) variables for coral reef fishes. Overall, adjacent habitat variables were as important as local reef variables in explaining reef fish density and biomass, despite being fewer in number in final models. For adult and juvenile wrasses (Labridae), and juveniles of some parrotfish taxa (Chlorurus), adjacent habitat was more important in explaining fish density and biomass. Notably, wrasses were positively influenced by the amount of sand and macroalgae in the adjacent seascape. Adjacent habitat metrics with the highest relative importance were sand (positive), macroalgae (positive), and mangrove habitats (negative), and fish responses to these metrics were consistent across fish groups evaluated. The 500‐m spatial scale was selected most often in models for seascape variables. Local coral reef variables with the greatest importance were percent cover of live coral (positive), sand (negative), and macroalgae (mixed). Incorporating spatial metrics that describe the surrounding seascape will capture more holistic patterns of fish–habitat relationships on reefs. This is important in regions where protection of reef fish habitat is an integral part of fisheries management but where protection of nonreef habitats is often overlooked.     

Untangling Natural Seascape Variation from Marine Reserve Effects Using a Landscape Approach

Distinguishing management effects from the inherent variability in a system is a key consideration in assessing reserve efficacy. Here, we demonstrate how seascape heterogeneity, defined as the spatial configuration and composition of coral reef habitats, can mask our ability to discern reserve effects. We then test the application of a landscape approach, utilizing advances in benthic habitat mapping and GIS techniques, to quantify this heterogeneity and alleviate the confounding influence during reserve assessment. Seascape metrics were quantified at multiple spatial scales using a combination of spatial image analysis and in situ surveys at 87 patch reef sites in Glover''s Reef Lagoon, Belize, within and outside a marine reserve enforced since 1998. Patch reef sites were then clustered into classes sharing similar seascape attributes using metrics that correlated significantly to observed variations in both fish and coral communities. When the efficacy of the marine reserve was assessed without including landscape attributes, no reserve effects were detected in the diversity and abundance of fish and coral communities, despite 10 years of management protection. However, grouping sites based on landscape attributes revealed significant reserve effects between site classes. Fish had higher total biomass (1.5×) and commercially important biomass (1.75×) inside the reserve and coral cover was 1.8 times greater inside the reserve, though direction and degree of response varied by seascape class. Our findings show that the application of a landscape classification approach vastly improves our ability to evaluate the efficacy of marine reserves by controlling for confounding effects of seascape heterogeneity and suggests that landscape heterogeneity should be considered in future reserve design.     

Hierarchical and scale‐dependent effects of fishing pressure and environment on the structure and size distribution of parrotfish communities

Parrotfishes are considered to have a major influence on coral reef ecosystems through grazing the benthic biota and are also primary fishery targets in the Indo‐Pacific. Consequently, the impact of human exploitation on parrotfish communities is of prime interest. As anthropogenic and environmental factors interact across spatial scales, sampling programs designed to disentangle these are required by both ecologists and resource managers. We present a multi‐scale examination of patterns in parrotfish assemblage structure, size distribution and diversity across eight oceanic islands of Micronesia. Results indicate that correlates of assemblage structure are scale‐dependent; biogeographic distributions of species and island geomorphology hierarchically influenced community patterns across islands whereas biophysical features and anthropogenic pressure influenced community assemblage structure at the within‐island scale. Species richness and phylogenetic diversity increased with greater broad‐scale habitat diversity associated with different island geomorphologies. However, within‐island patterns of abundance and biomass varied in response to biophysical factors and levels of human influence unique to particular islands. While the effect of fishing activities on community composition and phylogenetic diversity was obscured across island types, fishing pressure was the primary correlate of mean parrotfish length at all spatial scales. Despite widespread fishery‐induced pressure on Pacific coral reefs, the structuring of parrotfish communities at broad spatial scales remains a story largely dependent on habitat. Thus, we propose better incorporation of scale‐dependent habitat effects in future assessments of overexploitation on reef fish assemblages. However, strong community‐level responses within islands necessitate an improved understanding of the phylogenetic and functional consequences of altering community structure.     

Human activities as a driver of spatial variation in the trophic structure of fish communities on Pacific coral reefs

Anthropogenic activities such as land‐use change, pollution and fishing impact the trophic structure of coral reef fishes, which can influence ecosystem health and function. Although these impacts may be ubiquitous, they are not consistent across the tropical Pacific Ocean. Using an extensive database of fish biomass sampled using underwater visual transects on coral reefs, we modelled the impact of human activities on food webs at Pacific‐wide and regional (1,000s–10,000s km) scales. We found significantly lower biomass of sharks and carnivores, where there were higher densities of human populations (hereafter referred to as human activity); however, these patterns were not spatially consistent as there were significant differences in the trophic structures of fishes among biogeographic regions. Additionally, we found significant changes in the benthic structure of reef environments, notably a decline in coral cover where there was more human activity. Direct human impacts were the strongest in the upper part of the food web, where we found that in a majority of the Pacific, the biomass of reef sharks and carnivores were significantly and negatively associated with human activity. Finally, although human‐induced stressors varied in strength and significance throughout the coral reef food web across the Pacific, socioeconomic variables explained more variation in reef fish trophic structure than habitat variables in a majority of the biogeographic regions. Notably, economic development (measured as GDP per capita) did not guarantee healthy reef ecosystems (high coral cover and greater fish biomass). Our results indicate that human activities are significantly shaping patterns of trophic structure of reef fishes in a spatially nonuniform manner across the Pacific Ocean, by altering processes that organize communities in both “top‐down” (fishing of predators) and “bottom‐up” (degradation of benthic communities) contexts.     

Genetic signatures through space,time and multiple disturbances in a ubiquitous brooding coral

The predominance of self‐recruitment in many reef‐building corals has fundamental and complex consequences for their genetic diversity, population persistence and responses to climate change. Knowledge of genetic structure over local scales needs to be placed within a broad spatial context, and also integrated with genetic monitoring through time to disentangle these consequences. Here, we examined patterns of genetic diversity over multiple spatio‐temporal scales across tropical Australia in the ubiquitous brooding coral, Seriatopora hystrix. We also analysed complimentary environmental and demographic data to elucidate the seascape drivers of these patterns. Large genetic differences were detected between the east vs. west coasts of Australia. In northwest Australia, geographic differentiation dominated genetic structure over multiple scales. However, three sympatric lineages were detected at the largest offshore reef system (Scott Reef). Similar to the differences observed among putative species in eastern Australia, these lineages were associated with different levels of wave exposure. Local genetic structure within the Scott Reef system was relatively stable over 10 years, but temporal differences were observed that reflected small but important genetic changes over a few generations during recovery after severe bleaching. These results highlight the importance of self‐recruitment together with occasional longer distance connectivity for the persistence of a metapopulation across spatially and temporally variable environments. Our multidimensional research provides a foundation for further long‐term genetic monitoring to inform conservation strategies and highlights that sampling scales, ecological effects and cryptic diversity are important considerations to develop realistic understanding of the evolutionary resilience of corals.     

Local and Regional Impacts of Pollution on Coral Reefs along the Thousand Islands North of the Megacity Jakarta,Indonesia

Worldwide, coral reefs are challenged by multiple stressors due to growing urbanization, industrialization and coastal development. Coral reefs along the Thousand Islands off Jakarta, one of the largest megacities worldwide, have degraded dramatically over recent decades. The shift and decline in coral cover and composition has been extensively studied with a focus on large-scale gradients (i.e. regional drivers), however special focus on local drivers in shaping spatial community composition is still lacking. Here, the spatial impact of anthropogenic stressors on local and regional scales on coral reefs north of Jakarta was investigated. Results indicate that the direct impact of Jakarta is mainly restricted to inshore reefs, separating reefs in Jakarta Bay from reefs along the Thousand Islands further north. A spatial patchwork of differentially degraded reefs is present along the islands as a result of localized anthropogenic effects rather than regional gradients. Pollution is the main anthropogenic stressor, with over 80% of variation in benthic community composition driven by sedimentation rate, NO₂, PO₄ and Chlorophyll a. Thus, the spatial structure of reefs is directly related to intense anthropogenic pressure from local as well as regional sources. Therefore, improved spatial management that accounts for both local and regional stressors is needed for effective marine conservation.     

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.     

How much time can herbivore protection buy for coral reefs under realistic regimes of hurricanes and coral bleaching?

Coral reefs have been more severely impacted by recent climate instability than any other ecosystem on Earth. Corals tolerate a narrow range of physical environmental stress, and increases in sea temperature of just 1 °C over several weeks can result in mass coral mortality, often exceeding 95% of individuals over hundreds of square kilometres. Even conservative climate models predict that mass coral bleaching events could occur annually by 2050. Unfortunately, managers of coral‐reef resources have few options available to meet this challenge. Here, we investigate the role that fisheries conservation tools, including the designation of marine reserves, can play in altering future trajectories of Caribbean coral reefs. We use an individual‐based model of the ecological dynamics to test the influence of spatially realistic regimes of disturbance on coral populations. Two major sources of disturbance, hurricanes and coral bleaching, are simulated in contrasting regions of the Caribbean: Belize, Bonaire, and the Bahamas. Simulations are extended to 2099 using the HadGEM1 climate model. We find that coral populations can maintain themselves under all levels of hurricane disturbance providing that grazing levels are high. Regional differences in hurricane frequency are found to cause strikingly different spatial patterns of reef health with greater patchiness occurring in Belize, which has less frequent disturbance, than the Bahamas. The addition of coral bleaching led to a much more homogenous reef state over the seascape. Moreover, in the presence of bleaching, all reefs exhibited a decline in health over time, though with substantial variation among regions. Although the protection of herbivores does not prevent reef degradation it does delay rates of coral loss even under the most severe thermal and hurricane regimes. Thus, we can estimate the degree to which local conservation can help buy time for reefs with values ranging between 18 years in the Bahamas and over 50 years in Bonaire, compared with heavily fished systems. Ultimately, we demonstrate that local conservation measures can benefit reef ecosystem services but that their impact will vary spatially and temporally. Recognizing where such management interventions will either help or fail is an important step towards both achieving sustainable use of coral‐reef resources and maximizing resource management investments.     

Coral reefs modify their seawater carbon chemistry – case study from a barrier reef (Moorea,French Polynesia)

Changes in the carbonate chemistry of coral reef waters are driven by carbon fluxes from two sources: concentrations of CO₂ in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air‐sea flux of CO₂ driven by benthic community processes can exceed that due to increases in atmospheric CO₂ (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae, and sand. Building on data from previous carbon flux studies along a reef‐flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon (C_T) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity (A_T) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ω_a). We use the model to test how changes in atmospheric CO₂ forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream–downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies.     

Isolation by resistance across a complex coral reef seascape

A detailed understanding of the genetic structure of populations and an accurate interpretation of processes driving contemporary patterns of gene flow are fundamental to successful spatial conservation management. The field of seascape genetics seeks to incorporate environmental variables and processes into analyses of population genetic data to improve our understanding of forces driving genetic divergence in the marine environment. Information about barriers to gene flow (such as ocean currents) is used to define a resistance surface to predict the spatial genetic structure of populations and explain deviations from the widely applied isolation-by-distance model. The majority of seascape approaches to date have been applied to linear coastal systems or at large spatial scales (more than 250 km), with very few applied to complex systems at regional spatial scales (less than 100 km). Here, we apply a seascape genetics approach to a peripheral population of the broadcast-spawning coral Acropora spicifera across the Houtman Abrolhos Islands, a high-latitude complex coral reef system off the central coast of Western Australia. We coupled population genetic data from a panel of microsatellite DNA markers with a biophysical dispersal model to test whether oceanographic processes could explain patterns of genetic divergence. We identified significant variation in allele frequencies over distances of less than 10 km, with significant differentiation occurring between adjacent sites but not between the most geographically distant ones. Recruitment probabilities between sites based on simulated larval dispersal were projected into a measure of resistance to connectivity that was significantly correlated with patterns of genetic divergence, demonstrating that patterns of spatial genetic structure are a function of restrictions to gene flow imposed by oceanographic currents. This study advances our understanding of the role of larval dispersal on the fine-scale genetic structure of coral populations across a complex island system and applies a methodological framework that can be tailored to suit a variety of marine organisms with a range of life-history characteristics.     

Coral Reef Disturbance and Recovery Dynamics Differ across Gradients of Localized Stressors in the Mariana Islands

The individual contribution of natural disturbances, localized stressors, and environmental regimes upon longer-term reef dynamics remains poorly resolved for many locales despite its significance for management. This study examined coral reefs in the Commonwealth of the Northern Mariana Islands across a 12-year period that included elevated Crown-of-Thorns Starfish densities (COTS) and tropical storms that were drivers of spatially-inconsistent disturbance and recovery patterns. At the island scale, disturbance impacts were highest on Saipan with reduced fish sizes, grazing urchins, and water quality, despite having a more favorable geological foundation for coral growth compared with Rota. However, individual drivers of reef dynamics were better quantified through site-level investigations that built upon island generalizations. While COTS densities were the strongest predictors of coral decline as expected, interactive terms that included wave exposure and size of the overall fish assemblages improved models (R² and AIC values). Both wave exposure and fish size diminished disturbance impacts and had negative associations with COTS. However, contrasting findings emerged when examining net ecological change across the 12-year period. Wave exposure had a ubiquitous, positive influence upon the net change in favorable benthic substrates (i.e. corals and other heavily calcifying substrates, R² = 0.17 for all reeftypes grouped), yet including interactive terms for herbivore size and grazing urchin densities, as well as stratifying by major reeftypes, substantially improved models (R² = 0.21 to 0.89, lower AIC scores). Net changes in coral assemblages (i.e., coral ordination scores) were more sensitive to herbivore size or the water quality proxy acting independently (R² = 0.28 to 0.44). We conclude that COTS densities were the strongest drivers of coral decline, however, net ecological change was most influenced by localized stressors, especially herbivore sizes and grazing urchin densities. Interestingly, fish size, rather than biomass, was consistently a better predictor, supporting allometric, size-and-function relationships of fish assemblages. Management implications are discussed.     

Extreme temperature events will drive coral decline in the Coral Triangle

In light of rapid environmental change, quantifying the contribution of regional‐ and local‐scale drivers of coral persistence is necessary to characterize fully the resilience of coral reef systems. To assess multiscale responses to thermal perturbation of corals in the Coral Triangle (CT), we developed a spatially explicit metacommunity model with coral–algal competition, including seasonal larval dispersal and external spatiotemporal forcing. We tested coral sensitivity in 2,083 reefs across the CT region and surrounding areas under potential future temperature regimes, with and without interannual climate variability, exploring a range of 0.5–2.0°C overall increase in temperature in the system by 2054. We found that among future projections, reef survival probability and mean percent coral cover over time were largely determined by the presence or absence of interannual sea surface temperature (SST) extremes as well as absolute temperature increase. Overall, reefs that experienced SST time series that were filtered to remove interannual variability had approximately double the chance of survival than reefs subjected to unfiltered SST. By the end of the forecast period, the inclusion of thermal anomalies was equivalent to an increase of at least 0.5°C in SST projections without anomalies. Change in percent coral cover varied widely across the region within temperature scenarios, with some reefs experiencing local extinction while others remaining relatively unchanged. Sink strength and current thermal stress threshold were found to be significant drivers of these patterns, highlighting the importance of processes that underlie larval connectivity and bleaching sensitivity in coral networks.     

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems

We quantify the relative importance of multi‐scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo‐Pacific biogeographical provinces. Large (>30 cm), functionally‐important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km²). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local‐scale variables, ‘distance from port’, a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re‐emphasise the importance that historical processes play in structuring contemporary biotic communities.     

Water column contributions to coral reef productivity: overcoming challenges of context dependence

Coral reefs are declining at an unprecedented rate. Effective management and conservation initiatives necessitate improved understanding of the drivers of production because the high rates found in these ecosystems are the foundation of the many services they provide. The water column is the nexus of coral reef ecosystem dynamics, and functions as the interface through which essentially all energy and nutrients are transferred to fuel both new and recycled production. Substantial research has described many aspects of water column dynamics, often focusing on specific components because water column dynamics are highly spatially and temporally context dependent. Although necessary, a cost of this approach is that these dynamics are often not well linked to the broader ecosystem or across systems. To help overcome the challenge of context dependence, we provide a comprehensive review of this literature, and synthesise it through the perspective of ecosystem ecology. Specifically, we provide a framework to organise the drivers of temporal and spatial variation in production dynamics, structured around five primary state factors. These state factors are used to deconstruct the environmental contexts in which three water column sub-food webs mediate ‘new’ and ‘recycled’ production. We then highlight critical pathways by which global change drivers are altering coral reefs via the water column. We end by discussing four key knowledge gaps hindering understanding of the role of the water column for mediating coral reef production, and how overcoming these could improve conservation and management strategies. Throughout, we identify areas of extensive research and those where studies remain lacking and provide a database of 84 published studies. Improved integration of water column dynamics into models of coral reef ecosystem function is imperative to achieve the understanding of ecosystem production necessary to develop effective conservation and management strategies needed to stem global coral loss.     

Identifying multiple coral reef regimes and their drivers across the Hawaiian archipelago

Loss of coral reef resilience can lead to dramatic changes in benthic structure, often called regime shifts, which significantly alter ecosystem processes and functioning. In the face of global change and increasing direct human impacts, there is an urgent need to anticipate and prevent undesirable regime shifts and, conversely, to reverse shifts in already degraded reef systems. Such challenges require a better understanding of the human and natural drivers that support or undermine different reef regimes. The Hawaiian archipelago extends across a wide gradient of natural and anthropogenic conditions and provides us a unique opportunity to investigate the relationships between multiple reef regimes, their dynamics and potential drivers. We applied a combination of exploratory ordination methods and inferential statistics to one of the most comprehensive coral reef datasets available in order to detect, visualize and define potential multiple ecosystem regimes. This study demonstrates the existence of three distinct reef regimes dominated by hard corals, turf algae or macroalgae. Results from boosted regression trees show nonlinear patterns among predictors that help to explain the occurrence of these regimes, and highlight herbivore biomass as the key driver in addition to effluent, latitude and depth.     

Benthic N2 fixation in coral reefs and the potential effects of human‐induced environmental change

Tropical coral reefs are among the most productive and diverse ecosystems, despite being surrounded by ocean waters where nutrients are in short supply. Benthic dinitrogen (N₂) fixation is a significant internal source of “new” nitrogen (N) in reef ecosystems, but related information appears to be sparse. Here, we review the current state (and gaps) of knowledge on N₂ fixation associated with coral reef organisms and their ecosystems. By summarizing the existing literature, we show that benthic N₂ fixation is an omnipresent process in tropical reef environments. Highest N₂ fixation rates are detected in reef‐associated cyanobacterial mats and sea grass meadows, clearly showing the significance of these functional groups, if present, to the input of new N in reef ecosystems. Nonetheless, key benthic organisms such as hard corals also importantly contribute to benthic N₂ fixation in the reef. Given the usually high coral coverage of healthy reef systems, these results indicate that benthic symbiotic associations may be more important than previously thought. In fact, mutualisms between carbon (C) and N₂ fixers have likely evolved that may enable reef communities to mitigate N limitation. We then explore the potential effects of the increasing human interferences on the process of benthic reef N₂ fixation via changes in diazotrophic populations, enzymatic activities, or availability of benthic substrates favorable to these microorganisms. Current knowledge indicates positive effects of ocean acidification, warming, and deoxygenation and negative effects of increased ultraviolet radiation on the amount of N fixed in coral reefs. Eutrophication may either boost or suppress N₂ fixation, depending on the nutrient becoming limiting. As N₂ fixation appears to play a fundamental role in nutrient‐limited reef ecosystems, these assumptions need to be expanded and confirmed by future research efforts addressing the knowledge gaps identified in this review.     

Spatial resilience of the Great Barrier Reef under cumulative disturbance impacts

In the face of increasing cumulative effects from human and natural disturbances, sustaining coral reefs will require a deeper understanding of the drivers of coral resilience in space and time. Here we develop a high‐resolution, spatially explicit model of coral dynamics on Australia's Great Barrier Reef (GBR). Our model accounts for biological, ecological and environmental processes, as well as spatial variation in water quality and the cumulative effects of coral diseases, bleaching, outbreaks of crown‐of‐thorns starfish (Acanthaster cf. solaris), and tropical cyclones. Our projections reconstruct coral cover trajectories between 1996 and 2017 over a total reef area of 14,780 km², predicting a mean annual coral loss of ?0.67%/year mostly due to the impact of cyclones, followed by starfish outbreaks and coral bleaching. Coral growth rate was the highest for outer shelf coral communities characterized by digitate and tabulate Acropora spp. and exposed to low seasonal variations in salinity and sea surface temperature, and the lowest for inner‐shelf communities exposed to reduced water quality. We show that coral resilience (defined as the net effect of resistance and recovery following disturbance) was negatively related to the frequency of river plume conditions, and to reef accessibility to a lesser extent. Surprisingly, reef resilience was substantially lower within no‐take marine protected areas, however this difference was mostly driven by the effect of water quality. Our model provides a new validated, spatially explicit platform for identifying the reefs that face the greatest risk of biodiversity loss, and those that have the highest chances to persist under increasing disturbance regimes.     

Patterns in Temporal Variability of Temperature,Oxygen and pH along an Environmental Gradient in a Coral Reef

Spatial and temporal environmental variability are important drivers of ecological processes at all scales. As new tools allow the in situ exploration of individual responses to fluctuations, ecologically meaningful ways of characterizing environmental variability at organism scales are needed. We investigated the fine-scale spatial heterogeneity of high-frequency temporal variability in temperature, dissolved oxygen concentration, and pH experienced by benthic organisms in a shallow coastal coral reef. We used a spatio-temporal sampling design, consisting of 21 short-term time-series located along a reef flat-to-reef slope transect, coupled to a long-term station monitoring water column changes. Spectral analyses revealed sharp gradients in variance decomposed by frequency, as well as differences between physically-driven and biologically-reactive parameters. These results highlight the importance of environmental variance at organismal scales and present a new sampling scheme for exploring this variability in situ.     

Seascape continuity plays an important role in determining patterns of spatial genetic structure in a coral reef fish

Detecting patterns of spatial genetic structure (SGS) can help identify intrinsic and extrinsic barriers to gene flow within metapopulations. For marine organisms such as coral reef fishes, identifying these barriers is critical to predicting evolutionary dynamics and demarcating evolutionarily significant units for conservation. In this study, we adopted an alternative hypothesis‐testing framework to identify the patterns and predictors of SGS in the Caribbean reef fish Elacatinus lori. First, genetic structure was estimated using nuclear microsatellites and mitochondrial cytochrome b sequences. Next, clustering and network analyses were applied to visualize patterns of SGS. Finally, logistic regressions and linear mixed models were used to identify the predictors of SGS. Both sets of markers revealed low global structure: mitochondrial Φ_ST = 0.12, microsatellite F_ST = 0.0056. However, there was high variability among pairwise estimates, ranging from no differentiation between sites on contiguous reef (Φ_ST = 0) to strong differentiation between sites separated by ocean expanses ≥ 20 km (maximum Φ_ST = 0.65). Genetic clustering and statistical analyses provided additional support for the hypothesis that seascape discontinuity, represented by oceanic breaks between patches of reef habitat, is a key predictor of SGS in E. lori. Notably, the estimated patterns and predictors of SGS were consistent between both sets of markers. Combined with previous studies of dispersal in E. lori, these results suggest that the interaction between seascape continuity and the dispersal kernel plays an important role in determining genetic connectivity within metapopulations.     

Island biogeography of Caribbean coral reef fish

Aim The goal of our study was to test fundamental predictions of biogeographical theories in tropical reef fish assemblages, in particular relationships between fish species richness and island area, isolation and oceanographic variables (temperature and productivity) in the insular Caribbean. These analyses complement an analogous and more voluminous body of work from the tropical Indo‐Pacific. The Caribbean is more limited in area with smaller inter‐island distances than the Indo‐Pacific, providing a unique context to consider fundamental processes likely to affect richness patterns of reef fish. Location Caribbean Sea. Methods We compiled a set of data describing reef‐associated fish assemblages from 24 island nations across the Caribbean Sea, representing a wide range of isolation and varying in land area from 53 to 110,860 km². Regression‐based analyses compared the univariate and combined effects of island‐specific physical predictors on fish species richness. Results We found that diversity of reef‐associated fishes increases strongly with increasing island area and with decreasing isolation. Richness also increases with increasing nearshore productivity. Analyses of various subsets of the entire data set reveal the robustness of the richness data and biogeographical patterns. Main conclusions Within the relatively small and densely packed Caribbean basin, fish species richness fits the classical species–area relationship. Richness also was related negatively to isolation, suggesting direct effects of dispersal limitation in community assembly. Because oceanic productivity was correlated with isolation, however, the related effects of system‐wide productivity on richness cannot be disentangled. These results highlight fundamental mechanisms that underlie spatial patterns of biodiversity among Caribbean coral reefs, and which are probably also are functioning in the more widespread and heterogeneous reefs of the Indo‐Pacific.