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.     

Eukaryotic plankton communities across reef environments in Bocas del Toro Archipelago,Panamá

Variation in light and temperature can influence the genetic diversity and structure of marine plankton communities. While open-ocean plankton communities receive much scientific attention, little is known about how environmental variation affects plankton communities on tropical coral reefs. Here, we characterize eukaryotic plankton communities on coral reefs across the Bocas del Toro Archipelago, Panamá. Temperature loggers were deployed, and midday light levels were measured to quantify environmental differences across reefs at four inshore and four offshore sites (Inshore = Punta Donato, Smithsonian Tropical Research Institute (STRI) Point, Cristobal, Punta Laurel and Offshore = Drago Mar, Bastimentos North, Bastimentos South, and Cayo de Agua). Triplicate vertical plankton tows were collected midday, and high-throughput 18S ribosomal DNA metabarcoding was leveraged to investigate the relationship between eukaryotic plankton community structure and inshore/offshore reef environments. Plankton communities from STRI Point were additionally characterized in the morning (~ 08:00), midday (~ 12:00), and late-day (~ 16:00) to quantify temporal variation within a single site. We found that inshore reefs experienced higher average seawater temperatures, while offshore sites offered higher light levels, presumably associated with reduced water turbidity on reefs further from shore. These significant environmental differences between inshore and offshore reefs corresponded with overall plankton community differences. We also found that temporal variation played a structuring role within these plankton communities, and conclude that time of community sampling is an important consideration for future studies. Follow-up studies focusing on more intensive sampling efforts across space and time, coupled with techniques that can detect more subtle genetic differences between and within communities will more fully capture plankton dynamics in this region and beyond.

     

How corals made rocks through the ages

Hard, or stony, corals make rocks that can, on geological time scales, lead to the formation of massive reefs in shallow tropical and subtropical seas. In both historical and contemporary oceans, reef‐building corals retain information about the marine environment in their skeletons, which is an organic–inorganic composite material. The elemental and isotopic composition of their skeletons is frequently used to reconstruct the environmental history of Earth's oceans over time, including temperature, pH, and salinity. Interpretation of this information requires knowledge of how the organisms formed their skeletons. The basic mechanism of formation of calcium carbonate skeleton in stony corals has been studied for decades. While some researchers consider coral skeletons as mainly passive recorders of ocean conditions, it has become increasingly clear that biological processes play key roles in the biomineralization mechanism. Understanding the role of the animal in living stony coral biomineralization and how it evolved has profound implications for interpreting environmental signatures in fossil corals to understand past ocean conditions. Here we review historical hypotheses and discuss the present understanding of how corals evolved and how their skeletons changed over geological time. We specifically explain how biological processes, particularly those occurring at the subcellular level, critically control the formation of calcium carbonate structures. We examine the different models that address the current debate including the tissue–skeleton interface, skeletal organic matrix, and biomineralization pathways. Finally, we consider how understanding the biological control of coral biomineralization is critical to informing future models of coral vulnerability to inevitable global change, particularly increasing ocean acidification.     

New insights into global patterns of ocean temperature anomalies: implications for coral reef health and management

Aim Coral reefs are widely considered to be particularly vulnerable to changes in ocean temperatures, yet we understand little about the broad‐scale spatio‐temporal patterns that may cause coral mortality from bleaching and disease. Our study aimed to characterize these ocean temperature patterns at biologically relevant scales. Location Global, with a focus on coral reefs. Methods We created a 4‐km resolution, 21‐year global ocean temperature anomaly (deviations from long‐term means) database to quantify the spatial and temporal characteristics of temperature anomalies related to both coral bleaching and disease. Then we tested how patterns varied in several key metrics of disturbance severity, including anomaly frequency, magnitude, duration and size. Results Our analyses found both global variation in temperature anomalies and fine‐grained spatial variability in the frequency, duration and magnitude of temperature anomalies. However, we discovered that even during major climatic events with strong spatial signatures, like the El Niño–Southern Oscillation, areas that had high numbers of anomalies varied between years. In addition, we found that 48% of bleaching‐related anomalies and 44% of disease‐related anomalies were less than 50 km², much smaller than the resolution of most models used to forecast climate changes. Main conclusions The fine‐scale variability in temperature anomalies has several key implications for understanding spatial patterns in coral bleaching‐ and disease‐related anomalies as well as for designing protected areas to conserve coral reefs in a changing climate. Spatial heterogeneity in temperature anomalies suggests that certain reefs could be targeted for protection because they exhibit differences in thermal stress. However, temporal variability in anomalies could complicate efforts to protect reefs, because high anomalies in one year are not necessarily predictive of future patterns of stress. Together, our results suggest that temperature anomalies related to coral bleaching and disease are likely to be highly heterogeneous and could produce more localized impacts of climate change.     

Scale-dependent spatial variability of coral assemblages along the Florida Reef Tract

 Coral reef communities of the western Atlantic have changed over the past two to three decades, but the magnitude and causes of this change remain controversial. Part of the problem is that small-scale patterns observed on individual reefs have been erroneously extrapolated to landscape and geographic scales. Understanding how reef coral assemblages vary through space is an essential prerequisite to devising sampling strategies to track the dynamics of coral reefs through time. In this paper we quantify variation in the cover of hard corals in spur-and-groove habitats (13–19 m depth) at spatial scales spanning five orders of magnitude along the Florida Reef Tract. A videographic sampling program was conducted to estimate variances in coral cover at the following hierarchical levels and corresponding spatial scales: (1) among transects within sites (0.01- to 0.1-km scale), (2) among sites within reefs (0.5- to 2-km scale), (3) among reefs within sectors of the reef tract (10- to 20-km scale), and (4) among sectors of the reef tract (50- to 100-km scale). Coral cover displayed low variability among transects within sites and among sites within reefs. This means that transects from a site adequately represented the variability of the spur-and-groove habitat of the reef as a whole. Variability among reefs within sectors was highly significant, compared with marginally significant variability among sectors. Estimates from an individual reef, therefore, did not adequately characterize nearby reefs, nor did those estimates sufficiently represent variability at the scale of the sector. The structure and composition of coral reef communities is probably determined by the interaction of multiple forcing functions operating on a variety of scales. Hierarchical analyses of coral assemblages from other geographic locations have detected high variability at scales different from those in the present study. A multiscale analysis should, therefore, precede any management decisions regarding large reef systems such as the Florida Reef Tract. Accepted: 19 July 1999     

Temporal patterns in coral reef, seagrass and mangrove communities from Chengue bay CARICOMP site (Colombia): 1993-2008

Few monitoring programs have simultaneously assessed the dynamics of linked marine ecosystems (coral reefs, seagrass beds and mangroves) to document their temporal and spatial variability. Based on CARICOMP protocol we evaluated permanent stations in coral reefs, seagrass beds and mangroves from 1993 to 2008 in Chengue Bay at the Tayrona Natural Park, Colombian Caribbean. Overall, the studied ecosystems showed a remarkable stability pattern over the monitoring period. While there were annual variations in coral reefs (coral cover) and mangroves (litterfall) caused by hurricane Lenny in 1999, particular trends in seagrass (leaf area index and leaf productivity) appear to reflect the natural variability in this ecosystem. We suggest that monitoring sites at the three marine ecosystems had in general a healthy development in the last 16 years. Our results are critical to locally improve the management strategies (Tayrona Natural Park) and to understand the long-term dynamics of closely associated marine ecosystems in the Caribbean.     

Characterization of measurement errors using structure‐from‐motion and photogrammetry to measure marine habitat structural complexity

Habitat structural complexity is one of the most important factors in determining the makeup of biological communities. Recent advances in structure‐from‐motion and photogrammetry have resulted in a proliferation of 3D digital representations of habitats from which structural complexity can be measured. Little attention has been paid to quantifying the measurement errors associated with these techniques, including the variability of results under different surveying and environmental conditions. Such errors have the potential to confound studies that compare habitat complexity over space and time. This study evaluated the accuracy, precision, and bias in measurements of marine habitat structural complexity derived from structure‐from‐motion and photogrammetric measurements using repeated surveys of artificial reefs (with known structure) as well as natural coral reefs. We quantified measurement errors as a function of survey image coverage, actual surface rugosity, and the morphological community composition of the habitat‐forming organisms (reef corals). Our results indicated that measurements could be biased by up to 7.5% of the total observed ranges of structural complexity based on the environmental conditions present during any particular survey. Positive relationships were found between measurement errors and actual complexity, and the strength of these relationships was increased when coral morphology and abundance were also used as predictors. The numerous advantages of structure‐from‐motion and photogrammetry techniques for quantifying and investigating marine habitats will mean that they are likely to replace traditional measurement techniques (e.g., chain‐and‐tape). To this end, our results have important implications for data collection and the interpretation of measurements when examining changes in habitat complexity using structure‐from‐motion and photogrammetry.     

Responses of the Metabolism of the Larvae of Pocillopora damicornis to Ocean Acidification and Warming

Ocean acidification and warming are expected to threaten the persistence of tropical coral reef ecosystems. As coral reefs face multiple stressors, the distribution and abundance of corals will depend on the successful dispersal and settlement of coral larvae under changing environmental conditions. To explore this scenario, we used metabolic rate, at holobiont and molecular levels, as an index for assessing the physiological plasticity of Pocillopora damicornis larvae from this site to conditions of ocean acidity and warming. Larvae were incubated for 6 hours in seawater containing combinations of CO₂ concentration (450 and 950 µatm) and temperature (28 and 30°C). Rates of larval oxygen consumption were higher at elevated temperatures. In contrast, high CO₂ levels elicited depressed metabolic rates, especially for larvae released later in the spawning period. Rates of citrate synthase, a rate-limiting enzyme in aerobic metabolism, suggested a biochemical limit for increasing oxidative capacity in coral larvae in a warming, acidifying ocean. Biological responses were also compared between larvae released from adult colonies on the same day (cohorts). The metabolic physiology of Pocillopora damicornis larvae varied significantly by day of release. Additionally, we used environmental data collected on a reef in Moorea, French Polynesia to provide information about what adult corals and larvae may currently experience in the field. An autonomous pH sensor provided a continuous time series of pH on the natal fringing reef. In February/March, 2011, pH values averaged 8.075±0.023. Our results suggest that without adaptation or acclimatization, only a portion of naïve Pocillopora damicornis larvae may have suitable metabolic phenotypes for maintaining function and fitness in an end-of-the century ocean.     

Rubble fields shape planktonic protist communities in Indonesia at a local scale

The Coral Triangle encompasses nearly 30% of the world's coral reefs and is widely considered the epicenter of marine biodiversity. Destructive fishing practices and natural disturbances common to this region damage reefs leaving behind fields of coral rubble. While the impacts of disturbances in these ecosystems are well documented on metazoans, we have a poor understanding of their impact on microbial communities at the base of the food web. We use metabarcoding to characterize protist community composition in sites of varying fisheries management schemes and benthic profiles across the island of Lombok, Indonesia. Our study shows that rubble coverage and net primary productivity are the strongest explainers of variation in protist communities across Lombok. More specifically, rubble fields are characterized by increases in small heterotrophic protists, including ciliates and cercozoans. In addition to shifts in heterotrophic protist communities, we also observed increases in diatom relative abundance in rubble fields, which corresponded to sites with higher net primary productivity. These results are the first to characterize protist communities in tropical marine rubble fields and provide insight on environmental factors potentially driving these shifts on a local scale.     

Government conservation policies on Mexican coastal areas: is "top-down" management working?

Marine and terrestrial ecosystems are declining globally due to environmental degradation and poorly planned resource use. Traditionally, local government agencies have been responsible of the management of natural reserves to preserve biodiversity. Nonetheless, much of these approaches have failed, suggesting the development of more integrative strategies. In order to discuss the importance of a holistic approach in conservation initiatives, coastal and underwater landscape value and biological/environmental indicators of coral reef degradation were assessed using the study case of Zihuatanejo, Guerrero coastal area. This area shelters representative coral reef structures of the Eastern Pacific coast and its terrestrial biodiversity and archaeology enhance the high value of its coastal area. This study explored the landscape value of both terrestrial and marine ecosystems using the geomorphosite approach in two sites on the Zihuatanejo coastal area: Caleta de Chon and Manzanillo Beach. Sedimentation rate, water transparency, chlorophyll and total suspended solids were recorded underwater in each site for environmental characterization. 50 photo-quadrants on five transects were surveyed between 3-4m depth to record coverage (%) of living corals, dead corals, algae, sand and rocks. The conservation status of coral reefs was assessed by the coral mortality index (MI). Landscape values showed that both terrestrial and marine ecosystems had important scientific and aesthetic values, being Manzanillo Beach the site with the highest potential for conservation initiatives (TtV = 14.2). However, coral reefs face elevated sedimentation rates (up to 1.16 kg/m2d) and low water transparency (less of 5m) generated by coastal land use changes that have increased soil erosion in the adjacent coastal area. High coverage of dead corals (23.6%) and algae (up to 29%) confirm the low values in conservation status of coral reefs (MI = 0.5), reflecting a poorly-planned management. Current conditions are the result of "top-down" conservation strategies in Zihuatanejo, as Federal and Municipal authorities do not coordinate, disregard local community in coral reef management, and ignore the intimate relationship between the coastal and marine realms. This work confirms the importance of conservation strategies with a holistic approach, considering both terrestrial and marine ecosystems in coastal areas; and that these initiatives should include local coastal communities in management and decision-taking processes done by government authorities.     

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.     

Diel Variability in Seawater pH Relates to Calcification and Benthic Community Structure on Coral Reefs

Community structure and assembly are determined in part by environmental heterogeneity. While reef-building corals respond negatively to warming (i.e. bleaching events) and ocean acidification (OA), the extent of present-day natural variability in pH on shallow reefs and ecological consequences for benthic assemblages is unknown. We documented high resolution temporal patterns in temperature and pH from three reefs in the central Pacific and examined how these data relate to community development and net accretion rates of early successional benthic organisms. These reefs experienced substantial diel fluctuations in temperature (0.78°C) and pH (>0.2) similar to the magnitude of 'warming' and 'acidification' expected over the next century. Where daily pH within the benthic boundary layer failed to exceed pelagic climatological seasonal lows, net accretion was slower and fleshy, non-calcifying benthic organisms dominated space. Thus, key aspects of coral reef ecosystem structure and function are presently related to natural diurnal variability in pH.     

Into the depth of population genetics: pattern of structuring in mesophotic red coral populations

Deep-sea reef-building corals are among the most conspicuous invertebrates inhabiting the hard-bottom habitats worldwide and are particularly susceptible to human threats. The precious red coral (Corallium rubrum, L. 1758) has a wide bathymetric distribution, from shallow up to 800 m depth, and represents a key species in the Mediterranean mesophotic reefs. Several studies have investigated genetic variability in shallow-water red coral populations, while geographic patterns in mesophotic habitats are largely unknown. This study investigated genetic variability of C. rubrum populations dwelling between 55 and 120 m depth, from the Ligurian to the Ionian Sea along about 1500 km of coastline. A total of 18 deep rocky banks were sampled. Colonies were analyzed by means of a set of microsatellite loci and the putative control region of the mitochondrial DNA. Collected data were compared with previous studies. Both types of molecular markers showed high genetic similarity between populations within the northern (Ligurian Sea and Tuscan Archipelago) and the southern (Tyrrhenian and Ionian seas) study areas. Variability in habitat features between the sampling sites did not affect the genetic variability of the populations. Conversely, the patchy distribution of suitable habitats affected populations’ connectivity within and among deep coral banks. Based on these results and due to the emphasis on red coral protection in the Mediterranean Sea by international institutions, red coral could be promoted as a ‘focal species’ to develop management plans for the conservation of deep coralligenous reefs, a reservoir of marine biodiversity.     

Recruitment of coral reef fishes along a cross-shelf gradient in the Red Sea peaks outside the hottest season

Knowledge on the early life history, ecology, and biology of marine species is crucial for future projections of the resilience of coral reef ecosystems and for adequate management strategies. A fundamental component of population dynamics is the recruitment of new individuals, and in some marine populations, this may be a limiting factor. Recruitment peaks of coral reef fishes commonly occur during the warmer months of the year in many subtropical and temperate locations worldwide. In the Red Sea, very little is known about the influence of temperature on reproductive patterns of coral reef fishes and studies on recruitment are missing. The Red Sea is one of the hottest and most isolated tropical seas in the world. We hypothesized that sea surface temperatures (SSTs) during the Red Sea’s hottest season may exceed the optimum for successful recruitment of some coral reef fishes, which therefore has to occur during other, cooler seasons, unlike recruitment among coral reef ecosystems around the world. We identified taxa among fish recruits by matching mitochondrial DNA sequences (using COI, commonly known as “barcoding”) and assessed potential biological and environmental drivers of recruitment. We studied three reefs located along a cross-shelf gradient for 12 consecutive months in the central Red Sea to capture seasonal changes in biotic and abiotic parameters along this gradient. Our results indicated that recruitment peaks did not occur during the hottest SSTs for most taxa, especially at the hottest inshore and mid-shelf reefs, and identified fish recruitment to be mainly and strongly correlated with the biomass of planktonic invertebrates. Moreover, temporal patterns of fish recruitment differed within and among taxonomic families among the reefs.

     

Diet and niche breadth variation in the marbled parrotfish,Leptoscarus vaigiensis,among coral reef sites in Kenya

Studies on feeding ecology of fishes are important for understanding ecosystem structure and function. This study tested the hypothesis of diet and niche breath variation in the marbled parrotfish (Leptoscarus vaigiensis) among coral reefs of different protection levels in Kenya. Fish samples were obtained from protected (Malindi and Watamu marine parks), moderately fished (Malindi and Watamu marine reserves) and highly fished (Vipingo and Kanamai) reefs. Total lengths of fish samples were measured and their stomach contents quantified using the point method. Seasonal dietary composition, niche breaths and feeding intensities were compared between the sites using multivariate statistics. Results showed the parrotfish is a predominantly reef macroalgal grazer. Fish from protected sites fed on diverse dietary items compared to those from reserves and highly fished sites. Fish niche breadths differed between sites and seasons. Higher niche breadths occurred in protected sites during the north‐east monsoon, while higher values occurred at fished sites during the south‐east monsoon season. This study, the first of its kind in Kenya and most of the western Indian Ocean, describes feeding in the marbled parrotfish and spatial variation in niche breadth as influenced by fishing pressure, environmental variability and biological interactions.     

Coral-algal competition on damaged reefs

Natural and anthropogenic catastrophes occurred at the end of the previous and in the beginning of the current centuries at the coral reefs of the World Ocean, and their consequences for the tropical shelf ecosystems have been described based on published data and our own investigations. It has been shown that in recent decades coral populations on reefs of tropical and subtropical regions of the World Ocean have been reduced by 80%, and in some areas have completely vanished. The biodiversity of reef ecosystems has been considerably reduced. The main reason for such changes is a 1-2°C increase in the temperature of surface waters in comparison with the monthly mean temperature in the hot season. The fate of the damaged coral reefs is under discussion. It is thought that in clean waters partially damaged coral reefs can recover, whereas in waters polluted as the result of human activity they collapse. The rate of coral reef restoration depends on the hydrological and hydrochemical conditions, frequency of natural calamities and competitive interrelation of algae and corals on the damaged sites of coral reefs. The nature of competitive interrelation between algae and corals is considered, viz., the dynamics of obliteration of damaged and dead coral colonies by various algal species, mechanisms of competitive interrelation, effects of the environment on the competitive ability of corals and algae, the internal and external conditions for victory in competitive activity. It has been suggested that coral reefs can be restored through temporary transformation into a vegetable reef. In the absence of natural calamities damaged reefs can be clearly restored to their original or altered state over several decades, but only in clean waters.     

Symbiotic specificity,association patterns,and function determine community responses to global changes: defining critical research areas for coral‐Symbiodinium symbioses

Climate change‐driven stressors threaten the persistence of coral reefs worldwide. Symbiotic relationships between scleractinian corals and photosynthetic endosymbionts (genus Symbiodinium) are the foundation of reef ecosystems, and these associations are differentially impacted by stress. Here, we couple empirical data from the coral reefs of Moorea, French Polynesia, and a network theoretic modeling approach to evaluate how patterns in coral‐Symbiodinium associations influence community stability under climate change. To introduce the effect of climate perturbations, we simulate local ‘extinctions’ that represent either the loss of coral species or the ability to engage in symbiotic interactions. Community stability is measured by determining the duration and number of species that persist through the simulated extinctions. Our results suggest that four factors greatly increase coral‐Symbiodinium community stability in response to global changes: (i) the survival of generalist hosts and symbionts maximizes potential symbiotic unions; (ii) elevated symbiont diversity provides redundant or complementary symbiotic functions; (iii) compatible symbiotic assemblages create the potential for local recolonization; and (iv) the persistence of certain traits associate with symbiotic diversity and redundancy. Symbiodinium may facilitate coral persistence through novel environmental regimes, but this capacity is mediated by symbiotic specificity, association patterns, and the functional performance of the symbionts. Our model‐based approach identifies general trends and testable hypotheses in coral‐Symbiodinium community responses. Future studies should consider similar methods when community size and/or environmental complexity preclude experimental approaches.     

The effects of marine heatwaves on acute heat tolerance in corals

Scleractinian coral populations are increasingly exposed to conditions above their upper thermal limits due to marine heatwaves, contributing to global declines of coral reef ecosystem health. However, historic mass bleaching events indicate there is considerable inter- and intra-specific variation in thermal tolerance whereby species, individual coral colonies and populations show differential susceptibility to exposure to elevated temperatures. Despite this, we lack a clear understanding of how heat tolerance varies across large contemporary and historical environmental gradients, or the selective pressures that underpin this variation. Here we conducted standardised acute heat stress experiments to identify variation in heat tolerance among species and isolated reefs spanning a large environmental gradient across the Coral Sea Marine Park. We quantified the photochemical yield (F_v/F_m) of coral samples in three coral species, Acropora cf humilis, Pocillopora meandrina, and Pocillopora verrucosa, following exposure to four temperature treatments (local ambient temperatures, and + 3°C, +6°C and + 9°C above local maximum monthly mean). We quantified the temperature at which F_v/F_m decreased by 50% (termed ED50) and used derived values to directly compare acute heat tolerance across reefs and species. The ED50 for Acropora was 0.4–0.7°C lower than either Pocillopora species, with a 0.3°C difference between the two Pocillopora species. We also recorded 0.9°C to 1.9°C phenotypic variation in heat tolerance among reefs within species, indicating spatial heterogeneity in heat tolerance across broad environmental gradients. Acute heat tolerance had a strong positive relationship to mild heatwave exposure over the past 35 years (since 1986) but was negatively related to recent severe heatwaves (2016–2020). Phenotypic variation associated with mild thermal history in local environments provides supportive evidence that marine heatwaves are selecting for tolerant individuals and populations; however, this adaptive potential may be compromised by the exposure to recent severe heatwaves.     

Prioritizing key resilience indicators to support coral reef management in a changing climate

Managing coral reefs for resilience to climate change is a popular concept but has been difficult to implement because the empirical scientific evidence has either not been evaluated or is sometimes unsupportive of theory, which leads to uncertainty when considering methods and identifying priority reefs. We asked experts and reviewed the scientific literature for guidance on the multiple physical and biological factors that affect the ability of coral reefs to resist and recover from climate disturbance. Eleven key factors to inform decisions based on scaling scientific evidence and the achievability of quantifying the factors were identified. Factors important to resistance and recovery, which are important components of resilience, were not strongly related, and should be assessed independently. The abundance of resistant (heat-tolerant) coral species and past temperature variability were perceived to provide the greatest resistance to climate change, while coral recruitment rates, and macroalgae abundance were most influential in the recovery process. Based on the 11 key factors, we tested an evidence-based framework for climate change resilience in an Indonesian marine protected area. The results suggest our evidence-weighted framework improved upon existing un-weighted methods in terms of characterizing resilience and distinguishing priority sites. The evaluation supports the concept that, despite high ecological complexity, relatively few strong variables can be important in influencing ecosystem dynamics. This is the first rigorous assessment of factors promoting coral reef resilience based on their perceived importance, empirical evidence, and feasibility of measurement. There were few differences between scientists' perceptions of factor importance and the scientific evidence found in journal publications but more before and after impact studies will be required to fully test the validity of all the factors. The methods here will increase the feasibility and defensibility of including key resilience metrics in evaluations of coral reefs, as well as reduce costs. Adaptation, marine protected areas, priority setting, resistance, recovery.     

Small-scale variability in the size structure of scleractinian corals around Moorea, French Polynesia: patterns across depths and locations

The size structure of coral populations is influenced by biotic and physical factors, as well as species-specific demographic rates (recruitment, colony growth, mortality). Coral reefs surrounding Moorea Island are characterized by strong environmental gradients at small spatial scales, and therefore, we expected that the size structure of coral populations would vary greatly at this scale. This study aimed at determining the degree of spatial heterogeneity in the population size structure of two coral taxa, Pocillopora meandrina and massive Porites spp., among depths (6, 12, and 18 m) and among locations (Vaipahu, Tiahura and Haapiti) representing different exposure to hydrodynamic forces. Our results clearly underlined the strong heterogeneity in the size structure of both P. meandrina and massive Porites spp., with marked variation among depths and among locations. However, the lack of any consistent and regular trends in the size structure along depths or among locations, and the lack of correlation between size structure and mean recruitment rates may suggest that other factors (e.g., stochastic life history processes, biotic interactions, and disturbances) further modify the structure of coral populations. We found that the size structure of P. meandrina was fundamentally different to that of massive Porites spp., reflecting the importance of life history characteristics in population dynamics. Handling editor: I. Nagelkerken