Coral reefs and other tropical marine ecosystems face catastrophic, accelerating degradation from a well-documented range of human pressures, yet conservation outcomes continue to lag far behind the pace of decline. I here outline a framework for successful management and conservation, consisting of five overall Objectives, and 12 general Principles of good process to achieve those objectives. The five objectives are: (1) Minimise direct, physical destruction of habitats. (2) Implement Marine Protected Areas or reserves to ensure a substantial proportion of area is protected from extractive/damaging activities. (3) Manage fishing (and hunting) outside reserves to protect not only stocks of target species but also habitats, food-webs and by-catch stocks. (4) Prevent/reduce water pollution, especially land-based runoff. (5) Address Climate Change impacts: Reduce CO2 emissions (mitigation) and maximise ecosystem resilience (adaptation). The principles are: People and Context: (1) The goal is sustainable benefits for both biodiversity and people. (2) Community engagement and stewardship are essential. (3) Learn from others, but management must be appropriate and specific for each place and context. Concepts and Frameworks for good management: (4) Apply concepts of integrated and Ecosystem-Based Management and Marine Spatial Planning. (5) Manage cumulative impacts. (6) Manage for uncertainty: Precautionary and adaptive management. (7) Manage for resilience, both ecological and social-economic. Knowledge, governance and finance: (8) Manage using the best available knowledge/science, especially social and economic information, but do not delay. (9) Compliance is critical, and requires both effective engagement and enforcement. (10) Governance is critical context for effective management. (11) Sustainable and sufficient finance, resourcing and capacity are vital. Solutions: (12) Focus on solutions, not problems. The accelerating rate and scale of pressures on reefs and related ecosystems requires development of further, more active and intervention-focused approaches, but these must be in addition to the approaches above, not alternatives. Indeed, the current situation demands much greater scale and urgency of conservation across all approaches, but most especially the 5 objectives outlined here.
Lifespans of animals inform us about generation length, underpinning assessments of extinction risk and models for fishery harvest strategies. Uncertainty and contention endure about the lifespans of coral reef echinoderms, especially soft-bodied sea cucumbers. We used a photographic mark–recapture study at Lizard Island, Australia, to validate longevity, growth and displacement in the large sea cucumber Bohadschia argus. This species is harvested in fisheries throughout the western central Pacific and Southeast Asia. Using the photographic mark–recapture method, four individuals, estimated to be up to 22 years old in 2012, were recaptured 11 years later. Most eye-spots on the matched individuals persisted over the study period. The recaptures confirmed a lifespan of at least 33 years and an estimated generation length of at least 21 years. Long-term growth of the individuals was modest, with body size increasing by just 0.2–1.3
Depth plays a crucial role in shaping marine biodiversity patterns, with species richness typically decreasing with depth. Despite extensive documentation of this pattern, the drivers of richness changes across depth remain unclear. Richness–depth patterns can arise from multiple proximate mechanisms acting simultaneously, such as changes in abundance, evenness, and the spatial aggregations of individuals. Using a unified framework, we examined variation in richness patterns and their underlying mechanisms in the northern Red Sea for fishes (down to 150 m), Scleractinia, Octocorallia, and Porifera (down to 45–70 m). Our results reveal taxa-specific richness responses. Overall, abundance changes emerged as the most consistent driver of richness variation with depth, although its direction and magnitude differed among taxa. Fish richness declined with depth, primarily driven by reduced abundance and lower evenness. In contrast, Porifera exhibited increased richness with depth, largely explained by higher abundances. Scleractinia richness peaked at 10 m and slowly declined with depth, similarly linked to changes in abundance. In contrast, Octocorallia showed a slight richness increase with depth, mainly due to higher evenness at greater depths, although gaps in observations at intermediate depths may have obscured fine-scale peaks within the studied range. Increasing sampling scale (by combining sampling units) amplified these patterns. The results highlight the importance of understanding abundance gradients for richness, which may be overlooked when relying solely on cover-based estimates. The taxon-specific variability in richness–depth patterns challenges the conventional expectation of declining richness with depth, yet uncovers important commonality in the underlying mechanisms.
Coral reefs worldwide are declining under multiple anthropogenic stressors, and competitive dynamics between corals and macroalgae are key determinants of reef condition and trajectory. Yet how environmental variation and herbivory jointly shape these interactions remains incompletely resolved. We conducted an 11-month observational field study across four fringing-reef sites on Culebra Island, Puerto Rico, spanning natural gradients in sedimentation, nutrient stoichiometry, seawater temperature, salinity, and Diadema antillarum density. Integrated benthic surveys, coral–macroalgae interaction assessments, and exploratory multivariate analyses revealed strong site-level differences in benthic organization. The two sites with higher sedimentation were characterized by lower coral cover and interaction patterns less favorable to coral persistence, whereas the lower-sedimentation sites retained higher coral cover and more mixed benthic assemblages. Macroalgal functional identity significantly influenced competitive outcomes with coral: Filamentous turf algae (FTA) won significantly more contact interactions than either fleshy macroalgae (FA) or coralline algae (CA), while FA was disproportionately represented at coral tissue margins at the two higher-sedimentation sites. Exploratory ordination was broadly consistent with these patterns, identifying sedimentation, D. antillarum density, and salinity as the variables most strongly associated with among-site differences in community structure, although the limited four-site observational design precludes strong causal inference. Overall, the results support a context-dependent view of coral–macroalgae interactions in which herbivory appears most likely to contribute to favorable benthic states where local environmental conditions are comparatively less stressful.
Shallow-water scleractinian corals are critical coral-reef architects that grow in especially saline ocean waters. While coral skeleton-based trace element proxies are the standard for evaluating past sea surface temperature (SST), global sea surface salinity (SSS) has been overlooked as a variable that may also be linked with coral skeletal geochemistry and mineralogy. The underpinnings of coral skeleton formation and its response to local environmental conditions are important when evaluating trace element-based paleoproxies and predicting coral health under future climate. Here, we systematically survey massive Porites species from the National Coral Collection that grew across a wide range of SSS ( 31–41 PSU) from around the world. Some paleoproxy-relevant trace element (TE)/Ca ratios (B, 87Sr, U, Li) positively correlate with SSS, but only U/Ca exhibits correlations with aragonite crystal unit cell parameters. The only clear correlation between SSS and unit cell parameters exists for b-axis lengthening for a subset of the samples growing at typical SSSs (30–36 PSU). As expected, SST is negatively correlated with SSS and expected TEs (87Sr, Li, Li/Mg) across the full dataset. Our quantitative crystallographic measurements also provide calcite phase
Crown-of-thorns starfish (CoTS: Acanthaster spp.) remain one of the foremost causes of coral mortality on coral reefs throughout the Indo West-Pacific, and recurrent population irruptions compound upon other major disturbances, especially climate-induced coral bleaching. Renewed scientific and management interest in CoTS stems from both the initiation of new and renewed population irruptions and sustained degradation of coral reef ecosystems. This perspective reflects on recent research advances and innovations in prediction, detection and responses to changing abundance and ecological impacts of CoTS, which were partly facilitated by a co-ordinated large-scale research program conducted on Australia’s GBR. The collection of papers in the subsequent Special Issue, together with other recent publications, highlight substantial advances in CoTS research, but also critical knowledge gaps and highly tractable and urgent research priorities.
Herbivorous coral reef fishes are often assigned to different functional groups based on feeding mode and presumed ecosystem processes, such as algal removal (i.e., functional herbivory). However, these functional assignments do not necessarily identify assimilated resources nor predict nutritional pathways supporting fish biomass. We used stable carbon and nitrogen isotopes of amino acids to refine our understanding of herbivory among three nominally herbivorous fishes: Chlorurus spilurus, Ctenochaetus striatus, and Naso lituratus. Amino acid carbon isotope fingerprinting indicated much higher and more variable algal carbon contribution for N. lituratus (52.0
Coral reefs are among the most biodiverse and productive ecosystems on Earth, yet increasingly frequent and intense marine heatwaves threaten the persistence of susceptible coral taxa. Identifying the traits that underpin variation in bleaching susceptibility is critical to understanding how corals with contrasting life-history strategies respond to thermal stress. Here, we examined relationships between physiology and bleaching severity in six coral taxa (arborescent Acropora, Goniastrea, Lobophyllia, Merulina, Pavona and Seriatopora) in the central Great Barrier Reef during the mass bleaching event which occurred in 2024. We also assessed changes in size frequency distributions of these taxa over a decade to determine whether physiological differences during bleaching mapped onto long-term demographic trends. Physiological traits differed among taxa, reflecting distinct energy acquisition and allocation strategies, but these traits alone did not adequately explain variation in bleaching severity, likely due to small-scale environmental and microhabitat effects. Over a decadal timescale, physiological and bleaching differences did not translate into consistent demographic shifts, indicating that environmental conditions can interact with traits in complex ways to drive among-species variation in demographic rates and responses to heat stress. To better understand relationships between coral physiology and long-term demographic trends, future studies should evaluate among-species differences in physiology over seasonal changes, ontogenetic phases and reproductive phenology. Taken together, these findings advance understanding of how physiological diversity among coral taxa can shape responses to ocean warming and highlight the need to integrate physiology, local environmental conditions and life-history strategies to predict coral persistence under future climate extremes.
Reef-building cold-water corals form large seabed structures known as coral mounds. As demonstrated in studies from the Northeast Atlantic and Mediterranean Sea, coral mounds accumulate large amounts of carbon(ate). However, beyond the scale of individual mounds, long-term accumulation of both organic (Corg) and inorganic carbon (Cinorg) at the mound province scale remains poorly quantified. In this study, we investigate the Campeche Mound Province, southern Gulf of Mexico, which consists of interconnected coral mound ridges covering an area of > 40 km2. Using sediment cores, we reconstruct total carbon (Corg and Cinorg) accumulation in the Campeche Mounds over the past 250 kyr. The results show mean total carbon accumulation rates of 0.5–5.6 g C cm−2 kyr−1. This is three to nine times higher than on the surrounding seafloor. We then upscale obtained carbon concentration data to the entire mound province using high-resolution bathymetry and the CoMMa toolbox, a novel morphometric mapping tool. The total carbon storage of the Campeche Mounds amounts to an estimated 18.5 megatons of carbon that is transferred to the long-term carbon cycle and immobilised for millions of years. For the first time, we present a combination of core-based analysis and spatial mapping. Through accounting for different approaches and time scales, we provide reliable value ranges for carbon accumulation rates in coral mounds. The Campeche Mound Province is not fully mapped and likely much larger, highlighting the substantial, albeit overlooked long-term carbon burial through benthic deep-sea ecosystems in the southern Gulf of Mexico and beyond.
Coral reefs are experiencing increased frequency and severity of thermal stress events, underscoring the need for rapid and scalable methods to assess coral bleaching susceptibility. Quantifying bleaching responses typically relies on pulse-amplitude modulated (PAM) fluorometry, an expensive tool that limits widespread implementation. Digital photography, by contrast, is low-cost, accessible, and easily standardized, yet its quantitative potential remains underutilized. Here, we evaluated whether RGB image analysis can serve as an accessible proxy for physiological bleaching metrics using two coral species (Acropora hemprichii and Stylophora pistillata) in an acute heat-stress experiment. RGB values were extracted from coral fragments using a semi-automated segmentation pipeline, and 63 color indices were computed and correlated with PAM-derived Fv/Fm, Symbiodiniaceae cell density, chlorophyll content, and host protein content. We calculated D_toWhite, the Euclidean distance in CIELAB color space between each coral fragment and a co-imaged white reference patch, extracted directly from uncorrected photographs. Across both species, D_toWhite performed nearly identically to the best color-corrected index (DeltaE76). The stronger association of D_toWhite with Symbiodiniaceae cell density and chlorophyll content compared to Fv/Fm reflects their distinct biological axes: D_toWhite tracks Symbiodiniaceae and pigment loss while Fv/Fm reflects photochemical efficiency. Green-weighted indices best approximated Fv/Fm and host protein content, demonstrating that a single standardized image can simultaneously provide information about bleaching severity and Symbiodiniaceae photophysiological state. These results demonstrate that a simple whitening metric derived from uncorrected photographs provides a reliable, scalable, and inexpensive proxy for bleaching severity, supporting higher-throughput thermal tolerance screening in resource-limited settings.
Recruitment is a critical demographic bottleneck that governs coral population persistence and reef recovery, yet the fine-scale environmental gradients that regulate settlement remain poorly resolved. Submarine groundwater discharge (SGD) creates spatially structured, multivariate biogeochemical gradients in nearshore reefs, altering salinity, carbonate chemistry, and nutrient availability. Here, we tested whether SGD regulates settlement of the brooding coral Pocillopora acuta through physiological effects on larvae and demographic feedbacks mediated by adult coral populations. We combined controlled 24-h settlement experiments using groundwater–seawater dilutions with an 8-month in situ deployment of settlement tiles along natural SGD gradients at two reefs in Moorea, French Polynesia, characterized by distinct groundwater chemistry and hydrodynamics. In laboratory assays, settlement responses to SGD were site dependent: Larvae exposed to groundwater from one site exhibited increased settlement with increasing SGD influence, whereas no effect of SGD was detected at the second site. In situ, SGD exhibited nonlinear relationships with both adult Pocillopora cover and settler abundance at one reef, peaking at intermediate groundwater influence. Across both reefs, adult coral cover positively predicted settler density, consistent with a demographic feedback linking local stock to recruitment. Together, these results demonstrate that SGD can directly alter larval settlement and indirectly regulate recruitment by restructuring adult populations. Our findings reveal that spatially heterogeneous, land-based inputs may fuel demographic feedbacks at ecologically relevant scales. As groundwater fluxes shift with climate change, understanding how multivariate environmental gradients shape recruitment will be essential for predicting reef resilience in a rapidly changing world.
Smaller animals may have an enhanced ability to convert microscopic food into biomass, a form of energy that is accessible to larger predators. Small-bodied cryptobenthic reef fishes (CRFs) exploit a variety of small food items and may themselves be important food sources for other coral reef dwellers. However, knowledge regarding the trophic niches of small and abundant CRFs of the genus Trimma is lacking. The aim of this study was to investigate the trophic dynamics of Trimma benjamini, T. capostriatum, and T. yanoi by examining their feeding behaviour, food items consumed, food origins (benthic or pelagic), trophic interactions, and ecological morphology. The majority of individuals (79.7–93.4
Coral reefs of the Florida Keys experienced the hottest summer on record in 2023, causing mass bleaching and mortality of scleractinian corals. Sea surface temperatures remained above 31°C for 41 days, exceeding all prior records for the region. Branching corals fared especially poorly, especially Acropora palmata, which has now been deemed functionally extinct across the entire Florida Reef Tract. High temperatures and prolonged thermal stress were the major causes of mortality. Our study investigates additional stressors contributing to coral mortality during the heatwave. Using benthic imagery, we show that during bleaching, coral tissue death is accelerated by proximity to disease. Using a Cox proportional hazard model, we found that, compared to initially healthy tissue on the same colony, disease lesions and neighboring tissue had a 3.8 times and 1.5 times higher risk of death, respectively. We show that these two stressors, working at different spatial scales, acted synergistically to increase mortality. Furthermore, from our in situ reef structural measurements, we found that during bleaching, coral survival was greatest along the reef edge. The reef displaces water, resulting in faster local velocity, which we hypothesize reduces the boundary layer at the tissue-water interface and thus simultaneously enhances the removal of cytotoxic metabolic wastes and the opportunity for coral heterotrophic feeding. Our findings reinforce the importance of the interactive effects of disease and reef topography on coral mortality, and suggest that restoration efforts should focus on reef edges where the chance of survival is improved relative to the reef interior.
While corals from high-latitude marginal reefs are hypothesized to possess enhanced stress tolerance, their acclimatization mechanisms to local environmental fluctuations, particularly seasonal light and temperature variations, remain incompletely characterized. This study investigated the trophic strategies of three coral species (Galaxea fascicularis, Pocillopora damicornis, and Acropora hyacinthus) on Luhuitou reef, a relatively high-latitude reef in China subject to pronounced seasonal shifts between rising-temperature, high-light springs and cooling-temperature, low-light autumns. We assessed trophic plasticity by integrating seasonal measurements of photosynthetic performance, energy reserve dynamics, and stable isotope signatures. Clear interspecific differences in seasonal responses were observed. By adopting a heterotrophically reliant dual assurance strategy, G. fascicularis increased both heterotrophic input and photosynthetic capacity, which together helped to counterbalance the loss in photosynthetic efficiency resulting from its elevated symbiont populations in autumn. Pocillopora damicornis relied on enhanced photosynthetic efficiency under baseline heterotrophy, optimizing light capture during low-light periods in autumn. Acropora hyacinthus maintained a mixotrophic strategy, exhibiting minimal seasonal shift and thus the lowest trophic flexibility among the studied species. These findings highlight that there is no single optimal strategy for highly variable reef systems, but rather that interspecific variation in trophic strategy is critical to community resilience under environmental change.
The increasing frequency and intensity of thermal anomalies, combined with local stressors, have reshaped our understanding of coral thermal vulnerability worldwide. In this study, we tracked bleaching and mortality trajectories across eight surveys conducted during the fourth global mass bleaching event in 2024, which reached 21.37 °C-weeks in the study region. We individually monitored 290 colonies from eight major reef-building species in a Northeastern Brazilian coastal reef using video and photographic surveys, complemented by 3D models for data validation. Our results revealed marked differences in species vulnerability, with mortality reaching 99
The ecological effects of high densities of crown-of-thorns starfish (CoTS, Acanthaster spp.) are driven by their cumulative feeding pressure on coral assemblages, making accurate predictions of feeding impacts essential for management. Despite this, a limited understanding of the spatiotemporal dynamics of feeding behaviour, and the environmental and biological drivers underlying them constrains our capacity to predict feeding impacts. We quantified daily feeding rates for 565 individual Western Pacific CoTS (Acanthaster cf. solaris) across a broad gradient of environmental conditions and population densities on Australia’s Great Barrier Reef (GBR). CoTS body size and local coral cover emerged as the strongest predictors of daily feeding rates, whilst population density, season, and water temperature had no significant effect. Notably, large CoTS (> 40 cm) at high coral cover sites consumed over ten times more coral tissue compared to smaller individuals (15–25 cm) at low coral cover sites, with mean daily consumption rates of 221.99 and 18.86 cm2 (planar area), respectively. These estimates of daily feeding are aggregated across all different coral genera consumed. We present estimates of daily feeding rates for different size classes and coral cover that are directly compatible with existing monitoring methodologies used on the GBR, providing ecologically relevant parameters to improve outbreak impact modelling and enable more accurate forecasting of coral loss for targeted CoTS control on the GBR.
This study examined early-stage recovery of the colorful outer mantle in Tridacna squamosa over 11 days at 26 °C following partial thermal bleaching at 31 °C. Recovery of symbiotic dinoflagellates was assessed through mantle coloration, symbiont density, transcript and protein levels of form II ribulose-1,5-bisphosphate carboxylase/oxygenase (Zoox-RBCII), and concentrations of total chlorophyll and peridinin. Host recovery was evaluated via iridocyte abundance and spatial organization using immunofluorescence microscopy with vacuolar H⁺-ATPase subunit A (ATP6V1A) as a marker and a novel quantification scheme. Restorations of transcript and protein levels of ATP6V1A and carbonic anhydrase 2-like (CA2), key enzymes in the host carbon concentrating mechanism (CCM), were also examined. Partial recovery occurred in giant clams returned to plain seawater at 26 °C, whereas NH4+ and PO43− supplementation substantially accelerated restoration across nearly all recovery metrics. Supplemented symbionts rapidly regained carbon fixation capacity, as increases in Zoox-RBCII protein abundance preceded rises in symbiont density. Notably, proliferation and reorganization of iridocytes essential for photosynthesis were evident as early as day 1 of recovery, with or without nutrient supplementation. Moreover, supplementation enhanced restoration of host ATP6V1A and CA2 protein abundances to levels exceeding pre-bleaching values on day 5 and 11, underscoring the pivotal role of the host CCM in supporting symbiont functional recovery. Overall, successful restoration of the T. squamosa–dinoflagellate bidirectional nutrient exchange depends on coordinated recovery of host photo-physiological system and symbiont photosynthesis, aided by sufficient nitrogen and phosphorus. Hence, inorganic nutrient supplementation may help mitigate thermal bleaching impacts on Indo-Pacific giant clams.
Coral reefs in the Persian/Arabian Gulf (PAG) are subject to extreme heat stress. Moreover, effects of temperature-induced bleaching on local coral assemblages are being further compounded by coral disease. This manuscript explores taxonomic and seasonal variation in disease prevalence, at Ras Ghanada, Abu Dhabi, from 2010 to 2024. Thirty-two image-based surveys were conducted across winter, spring, and summer seasons which looked at active diseases, partial mortality, bleaching, encroachment by neighboring biota and general health from images. Seafloor temperature was also recorded across the monitoring period. Elevated disease prevalence in 2013, 2019, 2021, and 2024 followed marked summer heat stress with significant coral bleaching. Disease was most prevalent in winter after summer thermal stress. Porites harrisoni showed highest disease prevalence, while species within the genus Dipsastraea spp. were more resilient. Acropora spp. suffered moderate disease prevalence after bleaching and disappeared from the Ras Ghanada dataset after 2015 likely as a result of both stressors. Relative prevalence of diseases increased from 1.42
On April 15th 2024 the National Oceanic and Atmospheric Association of the US announced the onset of the fourth global coral bleaching event, coinciding with the 2023-24 El Niño Southern Oscillation. Through a coordinated, nationwide collaboration of scientists, dive centers and citizen observers, we assessed bleaching responses across six reef regions in India, spanning most of the subcontinent’s major reef areas, from oceanic atolls and island slopes to mainland fringing and patchy reef formations. While bleaching intensity increased with accumulated heat stress (Degree Heating Weeks or DHW) as expected, it showed distinct regional variability, revealing the limits of DHW as a universal predictor. Among the regions, Lakshadweep was the most affected with severe bleaching even at intermediate DHW. In contrast, Mahatma Gandhi Marine National Park bleached less than other regions, likely reflecting cooling from large amplitude internal waves that could create mesoscale thermal refugia. Across sites, Acropora , Pocillopora , Galaxea , and Montipora , were the most affected genera while Pavona, Platygyra, Goniastrea and Favites were among the least affected. Palk Bay displayed a reversal of canonical genus-level susceptibilities, with only modest bleaching in the normally susceptible Acropora colonies, but high mortality in usually resistant Porites colonies. These contrasting regional and taxonomic responses highlight how context-specific resistance patterns, and local oceanography mediate thermal stress and underscore the need to integrate these local geographical contexts in our understanding of bleaching impacts on tropical reefs.
