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Recurrent climate-driven warming events, which can induce severe coral bleaching and mortality on tropical reefs, are predicted to cause homogenisation of coral communities and loss of ecosystem functions in shallow reef systems (< 30 m). However, data documenting the variation in coral carbonate production across depth are limited. Here we explore differences in coral cover, community composition, coral colony size structure and carbonate production rates between two depths (10 m and 17.5 m) across four atolls in the remote Chagos Archipelago. We show higher coral carbonate production rates at 10 m (4.82 ± 0.27 G, where G = kg CaCO3 m−2 yr−1) compared to sites at 17.5 m (3.1 ± 0.18 G). The main carbonate producers at 10 m consisted of fast-growing branching and tabular corals (mainly Acroporids) and massive corals (mainly Porites), with high abundances of medium- and large-sized colonies. In contrast, coral carbonate production at 17.5 m was driven by slow-growing encrusting and foliose morphotypes and small colony sizes. Utilising a dataset following 6–7 years of recovery after the 2015–2017 bleaching event, our results show that depth-homogenisation of coral communities was temporary and carbonate production rates at 10 m depth recovered quicker at 3 of 4 studied atolls. The exception is Great Chagos Bank where slower recovery of branching and tabular corals at 10 m has led to a longer-lasting depth-homogenisation of carbonate production rates. The latter example cautions that more frequent bleaching events may drive increasing homogenisation of carbonate production rates across depth gradients, with implications for vital reef geo-ecological functions. [ABSTRACT FROM AUTHOR]

Rapid acute heat stress assays are increasingly used to assess reef coral heat tolerance and identify resilient corals for research and restoration. However, concerns remain about (1) how representative they are of natural bleaching events, and (2) how reproducible they are in resolving differences in heat tolerance among corals. To address these gaps, we (1) compared rapid assays with an 8-day 'classic' bleaching experiment on Acropora pulchra genets (n = 20), and (2) tested and retested rapid assay responses of Acropora cervicornis (n = 85 genets) up to a year apart. In both species, rapid assays revealed a ~ 2.5 °C range in heat tolerance thresholds (Fv/Fm ED50s) among genets, and these thresholds were strongly predictive of individual bleaching responses in the classic bleaching experiment (R = 0.74). Retesting genets with rapid assays showed ED50 differences < 0.99 °C in 90% of cases (median = 0.47 °C), and controlling for environmental effects reduced these to < 0.54 °C (median = 0.23 °C). Even so, large differences (> 0.93 °C) were needed between two individual genets to reliably retest in the same rank order, though smaller margins were reproducible for groups (e.g., 0.29 °C for groups of 10). These results demonstrate that rapid assays may not resolve fine-scale individual heat tolerance differences, but they can easily identify top- and bottom-performing individuals, and differential tolerance between groups of corals. These findings provide critical validation and quantitative guidelines for the use of rapid assays, which may transform coral heat tolerance research and its applications to reef restoration. [ABSTRACT FROM AUTHOR]

Recovery of ecosystem function in the aftermath of climate extremes such as cyclones and marine heat waves occurs in contest of highly variable environmental conditions and more chronic disturbances such as ocean acidification, which can further alter community structure and function. The present study investigated short-term responses of reef-scale primary production (Net Ecosystem Production; NEP), calcification (Net Ecosystem Calcification; NEC) and community structure in 2018 and again five years later in 2022 on a coral reef flat in Lizard Island on Australia's Great Barrier Reef, between and following multiple consecutive stressors, namely two cyclones (2014 and 2015) and back-to-back bleaching events (2016–2017 and 2020). NEC in 2022 was highly variable compared to what it was in 2018. Conversely, NEP was higher in 2022 even though light availability was often reduced by cloud cover. High variability in NEC indicated that environmental parameters may have immediate impacts on carbonate chemistry in seawater and may largely and quickly affect short-term recovery trajectories. Therefore, comparison of metabolic rates over short time scales across decades should be done with caution. We also found that cover of calcifiers and particularly algae were highest in coral rubble suggesting that typical benthic surveys in the open reef flat largely underestimate their abundance and possible contribution to NEP and NEC. This study adds to the evidence that NEC and NEP might not be exclusively related to coral cover and likely not tied to vertical reef accretion. [ABSTRACT FROM AUTHOR]

In recent decades, extensive coral mortality throughout the Persian/Arabian Gulf (PAG) from thermal stress events has led to increasing reef degradation and the loss of biodiversity across the region. To quantify these dynamics, water temperatures and benthic cover were monitored on ten reefs spanning about 350 km in the Southeastern PAG (Abu Dhabi) over a 10-year period. Water temperatures measured on the reefs fell into cooler (2010–2015) and warmer (2015–2020) periods. 2010–2015 had lower mean winter minimum (19 °C vs. 19.56 °C) and lower mean summer maximum (35.3 °C vs. 35.8 °C, coral bleaching threshold is 35.7 °C). Over the decade, mass coral bleaching occurred in seven years with four bleaching years after 2015. Coral cover decreased by 78% while turf and coralline algae strongly increased (66% and 154%, respectively), and fleshy macroalgae also collapsed in cover (− 83%). Cyanobacteria increased by 980% from 2017–20 with concurrent coral bleaching but without becoming spatially dominant. Despite the decline in coral cover, no shift into a macroalgae-dominated system occurred. [ABSTRACT FROM AUTHOR]

The coral-dinoflagellate endosymbiosis is based on nutrient exchanges that impact holobiont energetics. Of particular concern is the breakdown or dysbiosis of this partnership that is seen in response to elevated temperatures, where loss of symbionts through coral bleaching can lead to starvation and mortality. Here we extend a dynamic bioenergetic model of coral symbioses to explore the mechanisms by which temperature impacts various processes in the symbiosis and to enable simulational analysis of thermal bleaching. Our model tests the effects of two distinct mechanisms for how increased temperature impacts the symbiosis: 1) accelerated metabolic rates due to thermodynamics and 2) damage to the photosynthetic machinery of the symbiont caused by heat stress. Model simulations show that the model can capture key biological responses to different levels of increased temperatures. Moderately increased temperatures increase metabolic rates and slightly decrease photosynthesis. The slightly decreased photosynthesis rates cause the host to receive less carbon and share more nitrogen with the symbiont. This results in temporarily increased symbiont growth and a higher symbiont/host ratio. In contrast, higher temperatures cause a breakdown of the symbiosis due to escalating feedback that involves further reduction in photosynthesis and insufficient energy supply for CO 2 concentration by the host. This leads to the accumulation of excess light energy and the generation of reactive oxygen species, eventually triggering symbiont expulsion and coral bleaching. Importantly, bleaching does not result from accelerated metabolic rates alone; it only occurs as a result of the photodamage mechanism due to its effect on nutrient cycling. Both higher light intensities and higher levels of DIN render corals more susceptible to heat stress. Conversely, heterotrophic feeding can increase the maximal temperature that can be tolerated by the coral. Collectively these results show that a bioenergetics model can capture many observed patterns of heat stress in corals, such as higher metabolic rates and higher symbiont/host ratios at moderately increased temperatures and symbiont expulsion at strongly increased temperatures. [ABSTRACT FROM AUTHOR]

Most comparative studies assessing reef health focus on living hard coral cover as the key metric. In Indonesia, in situ monitoring of coral cover has been ongoing for over five decades. However, as monitoring data and research findings are predominantly published in the local language (Bahasa Indonesia), local data often escape global attention, resulting in Indonesian coral reefs receiving less scientific attention despite accounting for ~ 15% of all coral reef area globally. Here, we systematically compiled both globally and locally published data on coral cover across Indonesia to assess changes over recent decades. We analysed 7,614 data entries extracted from 621 publications and found that the majority (79.1%) of the publications were written in Bahasa Indonesia, constituting 63.4% of the total data entries. Our dataset revealed limited evidence of net declines in coral cover over the last three decades (1994–2022). There was also no clear relationship between coral cover and human density, as well as with the thirteen environmental/anthropogenic drivers examined. We discuss several factors that may contribute to this lack of detectable large-scale change including: recent data potentially representing a 'shifted baseline'; the 'averaging out' of localised changes in coral cover dynamics at a broad scale; sampling biases; and/or the potential resilience of Indonesian coral reefs compared to other regions. This study highlights the wealth of accessible local coral reef data published in languages other than English and emphasises the importance of using such data to enhance our understanding of the long-term dynamics of coral reef ecosystems worldwide. [ABSTRACT FROM AUTHOR]

Background: Subtropical coral reefs are comparatively understudied compared to tropical coral reef ecosystems, yet also host a diverse and abundant array of marine life and provide substantial socio-economic benefits to communities. Research into the impacts of ocean warming on subtropical coral reefs has increased over the past two decades due to increase frequency and intensity of bleaching and degradation of these ecosystems. Understanding the extent of research effort and type of evidence assessing the response of subtropical corals and reefs to ocean warming provides valuable insight into global patterns in research efforts allowing critical knowledge gaps to be identified. A comprehensive understanding the impact of ocean warming on these systems will underpin our ability to predict and respond to future changes on subtropical coral reefs. Here, a systematic-map approach is used to identify recent research effort, from 2010 to 2023, and highlight patterns in the type, scale, and location of research conducted and as well as identify the availability of data and evidence reported. Methods: Primary literature was identified by searching Scopus and Science Citation Index Expanded through Web of Science Core Collection databases. The methodologies provided in a previously published systematic map protocol were applied, and 90 primary research publications were subsequently identified. Data extraction from the identified literature included bibliometric data, discipline and type of research, type of data reported and how it was recorded, and data availability. Findings: The identified literature consisted primarily of experimental (49%) and observational (39%) studies. The majority of the primary literature investigated corals in the ecoregions of Southern China (13%), Western Mediterranean (10%) and across a total of seven ecoregions grouped within Oceania (29%). Stressors reported in the literature as drivers of ocean warming reflect the standardisation of methods applied in reporting of events within the literature. Standardised metrics related to degree heating weeks (DHW) and marine heatwaves (MHW) have been reported when assessing the occurrence and severity of drivers, and are increasing in recent years, particularly in Australia. Finally, the need for increased research effort across much of the subtropics is evident, particularly for understudied regions such as the Western Indian Ocean where there are far fewer studies than other similar subtropical coral reef ecosystems. Conclusions: Climatic change, increasing ocean temperatures, and the impacts to subtropical and temperate coral reefs are of increasing concern to policy makers and researchers alike. This systematic map provides a broad overview of research topics and effort around the globe since 2010 and identifies areas where more research effort is urgently needed. Our study has identified major research clusters in Asia, Australia, the Mediterranean, and North America and gaps of research in regions such as the East Indian Oceans. Of the research conducted to date approximately one third reports on evidence related to marine protected areas and the vast majority of evidence is from close/territorial sea locations, providing important knowledge base for management of these areas. Of the 17 studies reporting on specific extreme events (rather than experimental studies which is the majority of evidence identified here) 13 have been published since 2019, with the majority reporting on events occurring in 2019/20 indicating a trend of increasing evidence in recent years (a total of 7 studies from 2010 to 2013, compared to over 10 studies published annually since 2019 up to mid-2023). [ABSTRACT FROM AUTHOR]

Atlantic reef-building corals and coral reefs continue to experience extensive decline due to increased stressors related to climate change, disease, pollution, and numerous anthropogenic threats. To understand the impact of ocean warming and reef loss on the estimated extinction risk of shallow water Atlantic reef-building scleractinians and milleporids, all 85 valid species were reassessed under the IUCN Red List Categories and Criteria, updating the previous Red List assessment of Atlantic corals published in 2008. For the present assessment, individual species declines were estimated based on the modeled coral cover loss (1989–2019) and projected onset of annual severe bleaching events (2020–2050) across the Atlantic. Species traits were used to scale species' relative vulnerability to the modeled cover declines and forecasted bleaching events. The updated assessments place 45.88%–54.12% of Atlantic shallow water corals at an elevated extinction risk compared to the previous assessments conducted in 2008 (15.19%–40.51%). However, coral cover loss estimates indicate an improvement in reef coverage compared to the historic time-series used for the 2008 assessments. Based on this, we infer that, although remaining dangerously high, the rate of Atlantic reef coral cover decline has surprisingly slowed in recent decades. However, based on modeled projections of sea-surface temperature that predict the onset of annual severe bleaching events within the next 30 years, we listed 26 (out of 85) species as Critically Endangered in the IUCN Red List. Each of these species had previously been listed under a lower threatened category and this result alone highlights the severe threat future bleaching events pose to coral survival and the reef ecosystems they support. [ABSTRACT FROM AUTHOR]

ABSTRACT Coral reef fisheries support livelihoods and provide an affordable source of essential dietary nutrients to coastal people. However, climate‐driven coral bleaching is dramatically altering reef habitats and changing reef fish composition, diversity, and productivity. We used data from fisheries independent surveys and artisanal trap landings to explore how reefs with different responses to coral bleaching differed in habitat configurations, fisheries catch rates, economic returns, and nutritional content. Coral‐associated fishes supported the highest catch rates, greatest species diversity, highest rates of economic returns for fishers, and a wide price range for consumers. Macroalgae‐associated fishes supported the greatest overall fisheries yields, which indicated higher fishery dependence on these habitats. Nutrient content was high in catches across all habitats, but concentrations varied by nutrient, which suggested that fishing across a range of reef habitats should provide the greatest variety of nutrients to coastal communities. [ABSTRACT FROM AUTHOR]

Coral bleaching, a consequence of stressed symbiotic relationships between corals and algae, has escalated due to intensified heat stress events driven by climate change. Despite global efforts, current early warning systems lack local precision. Our study, spanning 2015–2017 in the Mesoamerican Reef, revealed prevalent intermediate bleaching, peaking in 2017. By scrutinizing 23 stress exposure and sensitivity metrics, we accurately predicted 75% of bleaching severity variation. Notably, distinct thermal patterns—particularly the climatological seasonal warming rate and various heat stress metrics—emerged as better predictors compared to conventional indices (such as Degree Heating Weeks). Surprisingly, deeper reefs with diverse coral communities showed heightened vulnerability. This study presents a framework for coral reef bleaching vulnerability assessment, leveraging accessible data (including historical and real-time sea surface temperature, habitat variables, and species composition). Its operational potential lies in seamless integration with existing monitoring systems, offering crucial insights for conservation and management. A study on the Mesoamerican Reef shows that the climatological rate of seasonal warming and heat stress metrics more accurately predict coral bleaching severity than conventional indices, enhancing regional early warning systems for better conservation strategies. [ABSTRACT FROM AUTHOR]

Desert dust is an important source of essential metals for marine primary productivity, especially in oligotrophic systems surrounded by deserts, such as the Red Sea. However, there are very few studies on the effects of dust on reef-building corals and none on the response of corals to heat stress. We therefore supplied dust to two coral species (Stylophora pistillata and Turbinaria reniformis) kept under control conditions (26 °C) or heat stress (32 °C). Since dust releases large amounts of iron (Fe) in seawater, among other metals, the direct effect of different forms of Fe enrichment on coral photosynthesis was also tested. First, our results show that the desert dust altered the coral metallome by increasing the content of metals that are important for coral physiology (e.g. lithium (up to 5-fold), manganese (up to 4-fold in S. pistillata), iron (up to 3-fold in S. pistillata), magnesium (up to 1.3-fold), molybdenum (up to 1.5-fold in S. pistillata)). Overall, metal enrichment improved the photosynthetic performance of corals, especially under thermal stress (e.g. Pgross (up to 2-fold), Pnet (up to 10-fold), chlorophyll (up to 1.5-fold), symbionts (up to 1.6-fold)). However, Fe exposure (ferric chloride or ferric citrate) did not directly improve photosynthesis, suggesting that it is the combination of metals released by the dust, the so-called "metal cocktail effect", that has a positive impact on coral photophysiology. Dust also led to a decrease in Ni uptake (up to 1.4-fold in the symbionts), likely related to the nitrogen metabolism. Finally, we found that the isotopic signature of metals such as iron, zinc and copper is a good indicator of heat stress and dust exposure in corals. In conclusion, desert dust can increase coral resistance to bleaching by supplying corals with essential metals. [ABSTRACT FROM AUTHOR]

Sea temperature increases may compromise ecological restoration as a tool for recovering degraded coral reefs. A potential solution may lay within using corals with naturally higher thermal resilience, such as intertidal corals. This study aimed at comparing thermal resilience, growth and survival between intertidal and subtidal corals in a reciprocal transplant experiment. Sixty coral nurseries were installed in a shallow coral reef area in Kenya: half were placed in the intertidal zone and half in the subtidal zone. At both zones, intertidal and subtidal Pocillopora cf. damicornis coral fragments were cultured in equal proportions, resulting in 15 replicate nurseries for four treatments. After an initial culture phase of 1 month in situ, six nurseries per treatment were thermally stressed ex situ by exposing corals for 5 days to a temperature of 32 °C (3 °C above summer maximum), after which they were returned in situ to recover. Fragment brightness was measured as the response variable to thermal stress. Intertidal and subtidal corals increased brightness (i.e., bleached) at a similar rate, but during recovery intertidal corals returned quicker to their original brightness in both culture environments. Coral growth was highest for intertidal corals in the intertidal zone during cooler months and was highest for subtidal corals in the subtidal zone during peak temperatures. Intertidal corals transplanted to the subtidal zone registered the lowest survival. Thus, intertidal corals display higher thermal resilience through quicker recovery, but potential trade-offs require further investigation before these corals can be used as a climate-proof broodstock for reef restoration. [ABSTRACT FROM AUTHOR]

The 2014–2017 global coral bleaching event caused mass coral mortality and reshaped benthic communities across the Pacific. Swains Island (11.0° S, 171.1° W), a remote and uninhabited island within American Samoa, was exposed to moderate heat stress (6 °C-weeks) during this event. Temporal patterns in benthic cover and coral demography were monitored across 13 years straddling this heat stress event to assess the impacts across depth and the recovery trajectory. While Swains's reefs retain some of the highest calcifier cover in the US Pacific Islands, successional trajectories across depth following the 2016 heat stress suggest that these reefs are experiencing a more nuanced pattern of resilience to disturbance, with early signs of recovery in shallow reefs (3–6 m), a shift to non-calcifier dominance at mid depth (6–18 m), and stability on deep reefs (18–30 m). Shallow reefs experienced the largest changes with a relative 50% decline in coral cover, which was replaced by CCA between 2015 and 2018. Shifts in shallow coral community composition were strongly driven by the loss of Pocillopora and early recovery seven years after the event evidenced by an increase in small colonies. Mid-depth reefs experienced a 33% loss in coral cover between 2015 and 2023, and corresponding increase in upright macroalgae. The degree to which increasing macroalgae represents a temporary shift or gradual decline in calcifiers remains to be seen. While Swains's recovery bodes well for persistence of shallow reefs, its remoteness from broodstock and dominance of thermally sensitive taxa pose a threat to future climate resilience. [ABSTRACT FROM AUTHOR]

The article discusses the threats faced by coral reefs due to climate change, including bleaching and aggressive algal blooms. Scientists are working on ways to track and analyze reef health, as well as constructing artificial reefs to protect these ecosystems. Additionally, research shows that playing healthy reef sounds can encourage coral larvae to recolonize damaged reefs, offering hope for reef restoration efforts. French researchers have developed a non-invasive device to analyze dissolved compounds in seawater, providing insights into ecosystem health. [Extracted from the article]

Seawater temperature and the availability of dissolved inorganic nutrients (DINut) have a major influence on the stability of the symbiosis between corals and Symbiodiniaceae. In particular, seawater warming or DINut depletion can lead to coral bleaching, the loss of Symbiodiniaceae from coral tissue. However, the combined effects of heat stress and DINut deficiency on the coral energy metabolism are still understudied. Here, we investigated the physiological and energetic responses of the octocoral Heteroxenia fuscescens and the hexacoral Stylophora pistillata exposed to two levels of inorganic nutrients in seawater (control, depleted) and two temperatures, 25°C (control) and 30°C (high temperature), in a crossed factorial design. Our results show that thermal and DINut stress both decreased the photosynthesis to respiration ratio of the two species and induced bleaching in H. fuscescens. While nutrient deprivation had little effect on the corals' energy metabolism, heat stress led to higher concentrations of macromolecules such as carbohydrates and lipids, as well as anaerobic metabolism, and decreased ATP production in H. fuscescens. Given that the intensity and frequency of marine heatwaves will significantly increase in the future, there is an urgent need to investigate the processes by which corals can overcome starvation. [ABSTRACT FROM AUTHOR]

Understanding how coral reefs respond to disturbances is fundamental to assessing their resistance and resilience, particularly in the context of climate change. Due to the escalating frequency and intensity of coral bleaching events, it is essential to evaluate spatio-temporal responses of coral reef communities to disentangle the mechanisms underlying ecological changes. Here, we used benthic data collected from 59 reefs in the Red Sea over five years (2014–2019), a period that encompasses the 2015/2016 mass bleaching event. Reefs were located within three different geographic regions with different environmental settings: north (Duba; Al Wajh), central (Jeddah; Thuwal), and south (Al Lith; Farasan Banks; Farasan Islands). Coral community responses were region-specific, with communities in the south being more promptly affected than those in the northern and central regions, with hard and soft coral cover dropping drastically in several reefs from around > 40% to < 5% two years after bleaching. Coral bleaching effects were particularly evident in the decrease of cover in branching corals. Overall, we documented a shift towards a dominance of macroalgae, turf algae, and crustose coralline algae (CCA). Using remote sensing data, we analyzed sea surface temperature (SST) regimes at the study sites to infer potential drivers of changes in benthic composition. Both SST and Degree Heating Weeks (DHW) only partially aligned with the responses of benthic communities, highlighting the need for more accurate predictors of coral bleaching in the Red Sea. In times of intense coastal development along Saudi Arabia's Red Sea coast, our study provides crucial baseline information on developments in coral reef community composition, as well as to guide decision-making, namely restoration efforts. [ABSTRACT FROM AUTHOR]

The frequencies of marine heatwaves and thermal coral bleaching events (CBEs) over the Great Barrier Reef (GBR) continue to increase with five mass CBEs reported since 2016. While changes in the local meteorology, such as reduced wind speeds and decreased cloud cover, are known to heat the shallow reef waters, little consideration has been given to the overriding synoptic meteorology. The 2022 CBE, occurring under La Niña conditions, saw ocean temperatures at Davies Reef increase 1.9 °C over 19-days and subsequently cool 2.1 back to seasonal norms over eight days. This event was found to be triggered by repeated Rossby wave breaking disrupting the local trade winds, thus inhibiting the latent heat flux. Latent heat fluxes, the primary driver of the event, tripled as the trade winds returned via rapid coastal ridging. These same synoptic features are concurrent with the historic Lismore flooding located hundreds of kilometres south of the GBR. [ABSTRACT FROM AUTHOR]

El Niño typically induces cooling in the Southwest Pacific Ocean during austral summers, usually leading to decreased marine heatwave frequency and severity. However, the 2016 extreme El Niño unexpectedly coincided with the longest and most extensive marine heatwave ever recorded in the region. This heatwave, spanning over 1.7 million square kilometers, persisting for 24 days with a peak intensity of 1.5°C, resulted in massive coral bleaching and fish mortality. This exceptional warming resulted from anomalously strong shortwave radiation and reduced heat loss via latent heat fluxes, owing to low wind speed and increased air humidity. These anomalies are attributed to a rare combined event "Madden-Julian Oscillation and extreme El Niño." Following 10 February, the rapid dissipation of this marine heatwave results from the most intense cyclone ever recorded in the South Pacific. The hazardous ecological impacts of this extreme event highlight the needs for improving our understanding of marine heatwave-driving mechanisms that may result in better seasonal predictions. [ABSTRACT FROM AUTHOR]

The 1997/1998 El Niño event caused mass coral bleaching and mortality in many tropical and subtropical regions, including corals on Green Island, Taiwan, in the northwestern Pacific Ocean. This study analyzed coral carbon isotope ratios (δ13C), oxygen isotope ratios (δ18O), and Sr/Ca ratios for 29 years, including the 1997/1998 El Niño period, to examine how high water temperature events are recorded in coral geochemical indicators. Sr/Ca ratios in coral skeletons from Green Island show the lowest peak, means the highest temperature during the 1997/1998 El Niño period. However, we couldn't observe high-temperature events on δ18O. Furthermore, a negative δ13C shift was observed after El Niño events. The regime shift of δ13C might have been caused by temporal bleaching and/or a decrease in symbiotic algae due to high water temperature stress under the continuous decrease in δ13C in DIC due to the Suess effect. [ABSTRACT FROM AUTHOR]

The services provided by the world's coral reefs are threatened by increasingly frequent and severe marine heatwaves. Heatwave-induced degradation of reefs has often been inferred from the extent of the decline in total coral cover, which overlooks extreme variation among coral taxa in their susceptibility and responses to thermal stress. Here, we provide a continental-scale assessment of coral cover changes at 262 shallow tropical reef sites around Australia, using ecological survey data on 404 coral taxa before and after the 2016 mass bleaching event. A strong spatial structure in coral community composition along large-scale environmental gradients largely dictated how coral communities responded to heat stress. While heat stress variables were the best predictors of change in total coral cover, the pre-heatwave community composition best predicted the temporal beta-diversity index (an indicator of change in community composition over time). Indicator taxa in each coral community differed before and after the heatwave, highlighting potential winners and losers of climate-driven coral bleaching. Our results demonstrate how assessment of change in total cover alone may conceal very different responses in community structure, some of which showed strong regional consistency, and may provide a telling outlook of how coral reefs may reorganize in a warmer future. [ABSTRACT FROM AUTHOR]

ABSTRACT The current rapid climate warming is expected to cause an ocean temperature increase of 3°C–5°C by 2100, leading to deoxygenated and acidified tropical seas. Without mitigation measures, the total loss of tropical corals is inevitable. Already, one‐third of tropical reefs are considered permanently lost. Coral bleaching initiated by the loss of symbionts, the photosynthetic zooxanthellae, is the main process whereby corals respond to thermal stress, followed by recovery. However, increased thermal stress and frequency of bleaching have caused widespread coral recovery failure. Zooxantheallae of the genus Symbiodinium are considered the thermally vulnerable part of the coral symbiosis. In recent decades, warming has displaced genotypes of lower thermal resilience to subtropical latitudes; few genotypes of higher temperature tolerance remain abundant in tropical seas, but these will not withstand warming predictions either. Interestingly, high temperatures in the Red Sea have selected for exceptionally heat‐resistant coral genotypes and for the highest known thermal resilience in endemic zooxanthellae at the same time. Actions to overcome the coral bleaching crisis have been proposed by combining coral ecophysiology and mass culturing of thermally resilient Red Sea symbionts for naturalisation to the global tropical ocean, including restoration of collapsed reefs using corals with thermally resilient symbiont genotypes. [ABSTRACT FROM AUTHOR]

Tropical reef ecosystems are strongly influenced by the composition of coral species, but the factors influencing coral diversity and distributions are not fully understood. Here we demonstrate that large variations in the relative abundance of three major coral species across adjacent Caribbean reef sites are strongly related to their different low O2 tolerances. In laboratory experiments designed to mimic reef conditions, the cumulative effect of repeated nightly low O2 drove coral bleaching and mortality, with limited modulation by temperature. After four nights of repeated low O2, species responses also varied widely, from > 50% bleaching in Acropora cervicornis to no discernable sensitivity of Porites furcata. A simple metric of hypoxic pressure that combines these experimentally derived species sensitivities with high‐resolution field data accurately predicts the observed relative abundance of species across three reefs. Only the well‐oxygenated reef supported the framework‐building hypoxia‐sensitive Acropora cervicornis, while the hypoxia‐tolerant weedy species Porites furcata was dominant on the most frequently O2‐deplete reef. Physiological exclusion of acroporids from these O2‐deplete reefs underscores the need for hypoxia management to reduce extirpation risk. [ABSTRACT FROM AUTHOR]

Jeju Island, located in the northern East China Sea, is experiencing a rapid rise in water temperature due to climate change. This has led to the increased activity of subtropical species and extreme fluctuations in coastal ecosystems, such as macroalgal blooms and coral bleaching. Additionally, the region is experiencing more frequent and intense typhoons. This study investigated the green tides caused by Ulva, particularly Ulva ohnoi, a subtropical species, and the effects of typhoons on these blooms through photographic analysis of the Jeju coastline. The study area was consistently covered by Ulva species every August from 2020 to 2022. Super typhoons struck Jeju Island every September during the study period, with wind speeds exceeding 20 m/s. In 2020 and 2022, the green tides largely dissipated following the typhoons. This ironic outcome highlights how climate-driven increases in subtropical Ulva biomass are being mitigated by the increasing frequency of super typhoons. However, despite the impact of super typhoon Chanthu in September 2021, there was no significant reduction in the Ulva bloom area. This anomaly may be attributable to the dominant easterly wind system in 2021, as the study area faces east, preventing the typhoon from influencing the distribution of Ulva blooms. These findings suggest that the wind intensity and direction of annual typhoons play a critical role in determining the resolution of green tide outbreaks. [ABSTRACT FROM AUTHOR]

In the background of global warming, coral bleaching induced by elevated seawater temperature is the primary cause of coral reef degradation. Coral microbiome engineering using the beneficial microorganisms for corals (BMCs) has become a hot spot in the field of coral reef conservation and restoration. Investigating the potential of alleviating thermal stress by quorum quenching (QQ) bacteria may provide more tools for coral microbial engineering remediation. In this study, QQ bacteria strain Pseudoalteromonas piscicida SCSIO 43740 was screened among 75 coral-derived bacterial strains, and its quorum sensing inhibitor (QSI) compound was isolated and identified as 2,4-di-tert-butylphenol (2,4-DTBP). Then, the thermal stress alleviating potential of QQ bacteria on coral Pocillopora damicornis was tested by a 30-day controlled experiment with three different treatments: control group (Con: 29 °C), high temperature group (HT: 31 °C), and the group of high temperature with QQ bacteria inoculation (HTQQ: 31 °C + QQ bacteria). The results showed that QQ bacteria SCSIO 43740 inoculation can significantly mitigate the loss of symbiotic algae and impairment of photosynthesis efficiency of coral P. damicornis under thermal stress. Significant difference in superoxide dismutase (SOD) and catalase (CAT) enzyme activities between HT and HTQQ was not observed. In addition, QQ bacteria inoculation suppressed the coral microbial community beta-dispersion and improved the stability of microbial co-occurrence network under thermal stress. It was suggested that QQ bacteria inoculation can alleviate coral thermal stress via reshaping microbial interaction and maintain community stability of coral microbiome. This study provided new evidence for the probiotic function of QQ bacteria in corals, which shedding light on the development of new microbiological tools for coral reef conservation. [ABSTRACT FROM AUTHOR]

Coral bleaching is occurring more frequently as the climate changes, with multiple mass mortality events recently recorded on the Great Barrier Reef. Thermal stress coupled with high irradiance have previously been shown to be primary causes for coral bleaching. Therefore, a reduction in either of these pressures could reduce coral stress and eventual bleaching. Herein, we report the early development of a novel technology capable of reducing the amount of light entering a water body by ~20% in open ocean conditions. This mono-particle "sun shield" consists of an ultra-thin monolayer material and reflective calcium carbonate particles. The monolayer enables spreading of the particles into a thin film across the water surface, with only small amounts of material needed: 7.1 g/m2. A numerical modelling case study of residence times and the build-up of reactive oxygen stress in corals showed that the successful application of a stable film over the Lizard Island reef flat could reduce the reactive oxygen stress to below bleaching levels across approximately 1.5 km2 of reef area. With further development, mono-particle films such as this have the potential to be deployed over at-risk coral reefs at relatively small scales during predicted heatwave conditions, potentially reducing the severity of bleaching on coral reefs. [ABSTRACT FROM AUTHOR]

Hybridisation is an evolutionary process that generates genetic diversity in organisms. However, the relationship between reproductive features, such as spawning synchronisation and gamete compatibility, and the degree of introgression leading to hybridisation are poorly understood. The reef-building coral Acropora spp. have a complex evolutionary history, and the link between their ecology, life-history traits, and potential to hybridise is disputed. Here, we examined the relationship among the reproductive features involved in the intercrossing of three species, Acropora florida, Acropora gemmifera, and Acropora intermedia, at two sites: Akajima and the Sesoko islands in southern Japan. Although the examined species showed synchronous spawning and high rates of gamete compatibility, spawning synchronisation and gamete compatibility were less strongly associated with high rates of interbreeding among the three species. Model-based genetic clustering and site-pattern frequency-based tests with single nucleotide polymorphisms supported genetic admixture among the three species in each location. Demographic analyses using fastsimcoal implied that the admixture among the three species in each location might have occurred in the past (> 2,000 generations) and recently (< 50 generations). Furthermore, the recent admixture of these three species is potentially associated with heavy bleaching events and population declines. The principal component analysis, structure, and fastsimcoal showed that the extensive admixture of A. intermedia and A. gemmifera on Sesoko Island occurred recently. Therefore, gamete interactions that lead to hybridisation in the field must be clarified. Furthermore, the connectivity between the two locations needs to be identified; however, our results implied that population fluctuations could be associated with introgression. [ABSTRACT FROM AUTHOR]

Coral reefs are exposed to various environmental stressors that cause bleaching events, whereby endosymbiotic microalgae (Symbiodiniaceae) disassociate from coral hosts. Bleached corals are compromised and face mortality. The combination of high-light exposure and elevated seawater temperature often lead to coral bleaching. The physiological properties of the Symbiodiniaceae within the coral tissues contribute to the thermal tolerance of the holobiont (the host and all its symbionts). The present study aimed to investigate the effects of light and temperature stress on four Symbiodiniaceae species from three genera with respect to photosynthetic oxygen production and consumption. Under control conditions, the species displayed predominantly low-to-moderate light requirements for photosynthesis with increased photoinhibition at higher photon flux rates. After 30 days of heat acclimation at 32 °C, maximum photosynthetic activity declined in Effrenium voratum, doubled in Fugacium kawagutii, and remained unchanged in Breviolum psygmophilum. In subsequent acute heating assays, species-specific effects on maximum photosynthetic activity were observed. Photosynthesis in all species declined across a temperature gradient between 25 and 39 °C in the acute heating assays; full inhibition occurred at 37 °C in B. psygmophilum and E. voratum and at 39 °C in B. aenigmaticum and F. kawagutii. In contrast, respiration remained largely constant in all species across temperatures. Our data point to species-specific photophysiological traits that lead to different thermal tolerances among Symbiodiniaceae. [ABSTRACT FROM AUTHOR]

Rubble is ubiquitous on coral reefs and can aggregate into fields, forming a significant component of the reef substrate. Rubble fields often remain unconsolidated, with the component rubble pieces subject to movement that is dependent on hydrodynamic forcing, rubble size, shape, and other factors. Settlement of corals to rubble fields has long been assumed, but the dynamic movement of rubble pieces has been presumed to deter settlement and is thought to contribute to high post-settlement mortality. Rubble often forms on coral reefs following severe disturbances, and is predicted to increase under climate change, with the potential to impact settlement and recruitment-dependent recovery processes. Through a series of laboratory and field experiments, we demonstrate that corals from broadcast spawning species on the Great Barrier Reef will settle on unstable substrates, even those in constant motion. We also observed more coral spat on settlement tiles suspended in the water column than those fixed to the reef using a common approach to censusing settlement. Sampling of natural rubble on the reef 50 days after a mass-spawning event confirmed the presence of similar numbers of coral settlers on rubble and on tiles fixed to the reef. These results suggest that rubble fields are places of significant settlement for broadcast spawning corals. Suspended tiles were also surprisingly effective in collecting coral settlers, demonstrating that a change in sampling protocol can produce significant variation in settlement data and strengthening the argument for standardisation of settlement-monitoring protocols, particularly at a time of growing need for reliable metrics. These results also suggest that movement of rubble is not precluding settlement outright, but rather post-settlement processes (i.e. competition, predation, shading or burial by shifting rubble) are limiting recruitment to rubble patches. Consequently, rubble stabilisation may increase the survival of spat that have settled in these environments. [ABSTRACT FROM AUTHOR]

The degradation of tropical coral reefs continues unabated as global climate change causes mass "coral bleaching" events. At the organismal level, there is significant evidence that the production of reactive oxygen (ROS) and nitrogen (RNS) species, followed by programmed cell death, causes coral bleaching. Additionally, in tropical marine environments exposure to high irradiances of solar radiation contributes to the photooxidative production of ROS in corals. But most thermal stress experiments on corals have not manipulated and tested the direct and interactive effects of solar radiation on coral bleaching, which is further compounded by the ecologically unrealistic low irradiances used in many experiments. Using published data, a direct relationship between excitation pressure (Qm) on photosystem II for the photosymbionts of corals with irradiance, when exposed to thermal stress, is demonstrated here. Using these results, the photoinhibition model of oxidative stress and coral bleaching is refined for shallow coral reefs; high irradiances increase Qm and when exposed to thermal stress result in an increase in ROS and coral bleaching, but under low irradiances the production of ROS decreases while the production of RNS increases, leading to coral bleaching. This suggests that irradiance-dependent effector molecules of coral bleaching (i.e., ROS versus RNS) may dominant the oxidative stress landscape in the coral holobiont. Incorporating measurements of irradiance, tissue oxygen concentrations and ROS/RNS levels, in addition to temperature, into experiments and predictive models is required in order to better understand the full range of environmental conditions that cause coral bleaching. [ABSTRACT FROM AUTHOR]

When coral cover declines, numeric responses of parrotfish can facilitate top-down control of algae and help reefs recover. Yet many parrotfish are facultative corallivores and we know surprisingly little about how their numeric or functional responses to coral decline modify their interactions with coral prey to shape their impacts on surviving corals. Here, we use benthic and fish surveys conducted in the Florida Keys more than a decade apart to assess how coral communities have changed, and how these changes have impacted parrotfish and their predation rates on corals. We found that disturbances and disease have continued to drive declines in coral cover and changes in coral community composition, but that the parrotfish abundance has not changed. In turn, while parrotfish corallivory has remained relatively constant or even declined for some coral taxa, predation on preferred branching Porites species increased 10% in frequency and, when normalized to live tissue area, > 50% in intensity. These coral-mediated shifts in predation correlated with declines in conspecific cover and are indicative of depensatory predation, which can destabilize trophic interactions and drive prey to low densities or even extinction. While coral reefs cannot recover from disturbances without robust parrotfish populations, our study suggests that parrotfish corallivory has important ramifications for coral community structure and, after prolonged degradation, the ability of some diminished coral populations to recover or persist. In a world where corals bleach annually, understanding the functional responses of corallivorous parrotfish to changes in resource abundance will be increasingly important for effective ecosystem-based management. [ABSTRACT FROM AUTHOR]

High sea surface temperatures recorded in summer 2021 introduced a unique opportunity for 'real-time' assessment of Exmouth Gulf turbid reef's resilience to a marine heatwave event. Four sites along a turbidity and temperature gradient were surveyed during (March 2021) and after (October 2021) the event to assess bleaching rates (Bleaching Index = BI), differences in coral morphological responses to the heat wave, and post-event changes in benthic and coral community structure. Despite experiencing higher temperatures (> 30 °C) and Degree Heating Weeks (DHW = 8), the most turbid reef site, Somerville, displayed greater resilience to heat stress (BI = 14) compared to the "clear water" site, Bundegi (BI = 19.3), where temperatures never exceeded 30 °C (3 DHW). Our results also reveal that encrusting and massive corals, often considered more resilient to bleaching, displayed increased bleaching susceptibility at the turbid sites, potentially due to the synergistic effects of sedimentation and heat stress. In contrast, branching and foliose corals showed greater resilience to the heat wave in turbid water settings, while encrusting and branching corals exhibited lower resilience in the clearwater site. These findings highlight complex interactions between heat and reduced UV stress on turbid reefs potentially increasing resilience to bleaching but likely only for those coral morphologies that are not heavily impacted by sedimentation. [ABSTRACT FROM AUTHOR]

A mass coral bleaching event occurred in the summer of 2022 in subtropical Hong Kong, driven by two marine heatwaves (MHWs) with high intensities of 1.56 and 0.86 °C above a mean climate condition, both MHWs 7 days with a short gap of 4 days during the strong La Niña year. A transect survey was conducted at nine study sites in three regions, which revealed widespread coral bleaching with bleached coral cover ranging from 2.4 to 70.3%. In situ environmental data revealed the presence of a thermocline and halocline. Local conditions, including depth and wave exposure, significantly influenced the bleaching response. Shallow-water (2–4 m) corals were primarily affected, particularly in sheltered and moderately sheltered sites that exhibited higher levels of bleached coral cover (42.97 ± 15.4% and 44.93 ± 29.4%, respectively) compared to the exposed sites (31.8 ± 5.2%). Bleaching in deep waters (4–6 m) was minimal, with only a few colonies of Goniopora at two of the three sheltered sites exhibiting bleaching (1.7 ± 1.5%). Heat stress resistance differed between coral genera. Recovery rate for four common coral genera is low for Acropora tumida. Additionally, a minor hypoxia event was found to cause mortality of non-coral benthos at a sheltered site (Sharp Island). These findings highlight the alarming impact of extreme heatwaves on subtropical coral communities and underscore the importance of monitoring coral bleaching. [ABSTRACT FROM AUTHOR]

Abstract The frequencies of marine heatwaves and thermal coral bleaching events (CBEs) over the Great Barrier Reef (GBR) continue to increase with five mass CBEs reported since 2016. While changes in the local meteorology, such as reduced wind speeds and decreased cloud cover, are known to heat the shallow reef waters, little consideration has been given to the overriding synoptic meteorology. The 2022 CBE, occurring under La Niña conditions, saw ocean temperatures at Davies Reef increase 1.9 $$^\circ \hbox {C}$$ ∘ C over 19-days and subsequently cool 2.1 $$^\circ \hbox {C}$$ ∘ C back to seasonal norms over eight days. This event was found to be triggered by repeated Rossby wave breaking disrupting the local trade winds, thus inhibiting the latent heat flux. Latent heat fluxes, the primary driver of the event, tripled as the trade winds returned via rapid coastal ridging. These same synoptic features are concurrent with the historic Lismore flooding located hundreds of kilometres south of the GBR.

Abstract One of the main challenges in coral reef conservation and restoration is the identification of coral populations resilient under global warming. Seascape genomics is a powerful tool to uncover genetic markers potentially involved in heat tolerance among large populations without prior information on phenotypes. Here, we aimed to provide first insights on the role of candidate heat associated loci identified using seascape genomics in driving the phenotypic response of Acropora millepora from New Caledonia to thermal stress. We subjected 7 colonies to a long-term ex-situ heat stress assay (4 °C above the maximum monthly mean) and investigated their physiological response along with their Symbiodiniaceae communities and genotypes. Despite sharing similar thermal histories and associated symbionts, these conspecific individuals differed greatly in their tolerance to heat stress. More importantly, the clustering of individuals based on their genotype at heat-associated loci matched the phenotypic variation in heat tolerance. Colonies that sustained on average lower mortality, higher Symbiodiniaceae/chlorophyll concentrations and photosynthetic efficiency under prolonged heat stress were also the closest based on their genotypes, although the low sample size prevented testing loci predictive accuracy. Together these preliminary results support the relevance of coupling seascape genomics and long-term heat stress experiments in the future, to evaluate the effect size of candidate heat associated loci and pave the way for genomic predictive models of corals heat tolerance.

Light is critical to coral growth through endosymbiont photosynthesis but can also act with elevated temperatures to cause coral bleaching. When more light is absorbed than can be used for photosynthesis, elevated irradiance can damage symbiont photosynthetic machinery. Hence, solar-radiation management through shading has been suggested to alleviate coral bleaching during marine heatwaves. Acropora divaricata and Acropora kenti were tested at two temperatures with 30% shading and an unshaded control to determine the relative impacts of light and temperature on coral bleaching severity. The coral bleaching response was assessed by photochemical (pulse amplitude modulated fluorometry), physiological (symbiont density, chlorophyll a concentration, catalase activity, and lipid peroxidation), and physical (mean intensity of grey or 'percentage whiteness') markers. Shading significantly reduced the bleaching response in A. divaricata, whilst for some parameters A. kenti responded negatively to shade. In A. divaricata, shading prevented photochemical collapse up to the experiment's maximum 4.4 degree-heating weeks (DHW). Biomarkers of coral bleaching stress responded to shade and water temperature at 4.4 DHW; catalase activity was greatest in the shaded and ambient temperature treatment. Shading did not reduce the effects of bleaching in A. kenti; the mean intensity of grey and light saturation coefficient was greatest in the shaded treatment. Shading did, however, reduce lipid peroxidation at 3 DHW. Our results suggest shading during thermal stress may only protect some coral species, highlighting the need to consider species-specific responses when evaluating the potential efficacy of coral bleaching interventions. [ABSTRACT FROM AUTHOR]

Assisted sexual coral propagation, resulting in greater genet diversity via genetic recombination, has been hypothesized to lead to more adaptable and, hence, resilient restored populations compared to more common clonal techniques. Coral restoration efforts have resulted in substantial populations of 'Assisted sexual Recruits' (i.e., juvenile corals derived from assisted sexual reproduction; AR) of multiple species outplanted to reefs or held in in situ nurseries across many locations in the Caribbean. These AR populations provided context to evaluate their relative resilience compared to co-occurring coral populations during the 2023 marine heat wave of unprecedented duration and intensity that affected the entire Caribbean. Populations of six species of AR, most ranging in age from 1–4 years, were surveyed across five regions during the mass bleaching season in 2023 (Aug-Dec), alongside co-occurring groups of corals to compare prevalence of bleaching and related mortality. Comparison groups included conspecific adult colonies as available, but also the extant co-occurring coral assemblages in which conspecifics were rare or lacking, as well as small, propagated coral fragments. Assisted sexual recruits had significantly lower prevalence of bleaching impacts (overall pooled ~ 10%) than conspecific coral populations typically comprised of larger colonies (~ 60–100% depending on species). In addition, small corals derived from fragmentation (rather than sexual propagation) in two regions showed bleaching susceptibility intermediate between AR and wild adults. Overall, AR exhibited high bleaching resistance under heat stress exposure up to and exceeding Degree Heating Weeks of 20°C-weeks. As coral reefs throughout the globe are subject to increasingly frequent and intense marine heatwaves, restoration activities that include sexual reproduction and seeding can make an important contribution to sustain coral populations. [ABSTRACT FROM AUTHOR]

Summary: Coral thermal bleaching resilience can be improved by enhancing photosymbiont thermal tolerance via experimental evolution. While successful for some strains, selection under stable temperatures was ineffective at increasing the thermal threshold of an already thermo‐tolerant photosymbiont (Durusdinium trenchii). Corals from environments with fluctuating temperatures tend to have comparatively high heat tolerance. Therefore, we investigated whether exposure to temperature oscillations can raise the upper thermal limit of D. trenchii.We exposed a D. trenchii strain to stable and fluctuating temperature profiles, which varied in oscillation frequency. After 2.1 yr (54–73 generations), we characterised the adaptive responses under the various experimental evolution treatments by constructing thermal performance curves of growth from 21 to 31°C for the heat‐evolved and wild‐type lineages. Additionally, the accumulation of extracellular reactive oxygen species, photophysiology, photosynthesis and respiration rates were assessed under increasing temperatures.Of the fluctuating temperature profiles investigated, selection under the most frequent oscillations (diurnal) induced the greatest widening of D. trenchii's thermal niche. Continuous selection under elevated temperatures induced the only increase in thermal optimum and a degree of generalism.Our findings demonstrate how differing levels of thermal homogeneity during selection drive unique adaptive responses to heat in a coral photosymbiont. [ABSTRACT FROM AUTHOR]

Structural habitats support high biodiversity by providing refuge, forage resources, and recruitment habitat that upwardly influence the broader faunal community structure. However, there are few system-wide studies that empirically measure communities before and after major shifts in habitat structure or availability, limiting our ability to predict the consequences of changes in structural habitat above local scales. We used the collapse of the Apalachicola Bay, Florida oyster population as a natural experiment to assess the impacts of estuary-wide structural habitat loss on the nekton community through long-term faunal monitoring data. Habitat losses of this magnitude are expected to decrease diversity and alter composition, so we expected to observe these changes in Apalachicola Bay after the oyster population collapse. We assessed changes in Gini-Simpson diversity and composition over a 21-year period encompassing the 2012 oyster collapse using generalized linear mixed models to account for confounding drivers. We surprisingly found no evidence that Gini-Simpson diversity or composition differed immediately before or following the collapse, which may be explained if estuarine fauna were able to effectively use other habitats. This suggests that proportional changes in diversity or composition from loss or gain of structural habitats cannot be assumed at the system-wide scale. [ABSTRACT FROM AUTHOR]

Adaptation of reef-building corals to global warming depends upon standing heritable variation in tolerance traits upon which selection can act. Yet limited knowledge exists on heat-tolerance variation among conspecific individuals separated by metres to hundreds of kilometres. Here, we performed standardized acute heat-stress assays to quantify the thermal tolerance traits of 709 colonies of Acropora spathulata from 13 reefs spanning 1060 km (9.5° latitude) of the Great Barrier Reef. Thermal thresholds for photochemical efficiency and chlorophyll retention varied considerably among individual colonies both among reefs (approximately 6°C) and within reefs (approximately 3°C). Although tolerance rankings of colonies varied between traits, the most heat-tolerant corals (i.e. top 25% of each trait) were found at virtually all reefs, indicating widespread phenotypic variation. Reef-scale environmental predictors explained 12–62% of trait variation. Corals exposed to high thermal averages and recent thermal stress exhibited the greatest photochemical performance, probably reflecting local adaptation and stress pre-acclimatization, and the lowest chlorophyll retention suggesting stress pre-sensitization. Importantly, heat tolerance relative to local summer temperatures was the greatest on higher latitude reefs suggestive of higher adaptive potential. These results can be used to identify naturally tolerant coral populations and individuals for conservation and restoration applications. [ABSTRACT FROM AUTHOR]

Human activities and climate change have accelerated species losses and degradation of ecosystems to unprecedented levels. Both theoretical and empirical evidence suggest that extinction cascades contribute substantially to global species loss. The effects of extinction cascades can ripple across levels of ecological organization, causing not only the secondary loss of taxonomic diversity but also functional diversity erosion. Here, we take a step forward in coextinction analysis by estimating the functional robustness of reef fish communities to species loss. We built a tripartite network with nodes and links based on a model output predicting reef fish occupancy (113 species) as a function of coral and turf algae cover in Southwestern Atlantic reefs. This network comprised coral species, coral‐associated fish (site occupancy directly related to coral cover), and co‐occurring fish (occupancy indirectly related to coral cover). We used attack‐tolerance curves and estimated network robustness (R) to quantify the cascading loss of reef fish taxonomic and functional diversity along three scenarios of coral species loss: degree centrality (removing first corals with more coral‐associated fish), bleaching vulnerability and post‐bleaching mortality (most vulnerable removed first), and random removal. Degree centrality produced the greatest losses (lowest R) in comparison with other scenarios. In this scenario, while functional diversity was robust to the direct loss of coral‐associated fish (R = 0.85), the taxonomic diversity was not robust to coral loss (R = 0.54). Both taxonomic and functional diversity showed low robustness to indirect fish extinctions (R = 0.31 and R = 0.57, respectively). Projections of 100% coral species loss caused a reduction of 69% of the regional trait space area. The effects of coral loss in Southwestern Atlantic reefs went beyond the direct coral‐fish relationships. Ever‐growing human impacts on reef ecosystems can cause extinction cascades with detrimental consequences for fish assemblages that benefit from corals. [ABSTRACT FROM AUTHOR]

Ecosystem responses to disturbance depend on the nature of the perturbation and the ecological legacies left behind, making it critical to understand how climate‐driven changes in disturbance regimes modify resilience properties of ecosystems. For coral reefs, recent increases in severe marine heat waves now co‐occur with powerful storms, the historic agent of disturbance. While storms kill coral and remove their skeletons, heat waves bleach and kill corals but leave their skeletons intact. Here, we explored how the material legacy of dead coral skeletons modifies two key ecological processes that underpin coral reef resilience: the ability of herbivores to control macroalgae (spatial competitors of corals), and the replenishment of new coral colonies. Our findings, grounded by a major bleaching event at our long‐term study locale, revealed that the presence of structurally complex dead skeletons reduced grazing on turf algae by ~80%. For macroalgae, browsing was reduced by >40% on less preferred (unpalatable) taxa, but only by ~10% on more preferred taxa. This enabled unpalatable macroalgae to reach ~45% cover in 2 years. By contrast, herbivores prevented macroalgae from becoming established on adjacent reefs that lacked skeletons. Manipulation of unpalatable macroalgae revealed that the cover reached after 1 year (~20%) reduced recruitment of corals by 50%. The effect of skeletons on juvenile coral growth was contingent on the timing of settlement relative to the disturbance. If corals settled directly after bleaching (before macroalgae colonized), dead skeletons enhanced colony growth by 34%, but this benefit was lost if corals colonized dead skeletons a year after the disturbance once macroalgae had proliferated. These findings underscore how a material legacy from a changing disturbance regime can alter ecosystem resilience properties by disrupting key trophic and competitive interactions that shape post‐disturbance community dynamics. [ABSTRACT FROM AUTHOR]

Reef restoration has gained attention as it has strategic actions and powerful means in sustaining and maintaining coastal ecosystem services. This scientometric study systematically analyzes the current trends and research hotspot in coral restoration across the last five decades (1971–2022). The metadata (12,667 articles with 652,860 cited references) were obtained from the Clarivate Web of Science platform through the Core Collection database, associated with the CiteSpace and R‐software for further analysis. The results indicated that the trend of coral restoration is increasing in paper/year, with the United States, Australia, and China as major contributors to the related research. Furthermore, James Cook University, Australia had the largest number of articles, and the Consortium of Research Libraries of the United Kingdom was the most influential institution on coral restoration. The highly cited keywords are "Great Barrier Reef," "climate change," and "coral reef," while the most influential keywords are "coral," "model," and "Atlantic." A total of 23 clusters in the field with "coral reef," "phase shift," "bacterial communities," "coral restoration," "symbiotic dinoflagellate," "stony coral tissue loss disease," "bleaching event," "ocean acidification," "oyster reef," and "quantitative reconstruction" are among the top cluster size labeled. Early‐stage researcher may use both keywords and cluster analysis to find topics attractive to their future research projects. In addition, this study contributes toward evaluating recent scientific productivity about coral restoration as well as informing researchers and policymakers regarding funding, future strategic planning, and potential collaboration opportunities. [ABSTRACT FROM AUTHOR]

The deployment of engineered substrates seeded with newly settled corals is a technique being developed to increase the numbers of juvenile corals on reefs with the goal of improving reef resilience in response to climate warming. Using a hierarchical sampling design, we explored the spatial scales at which seeded coral (spat) survival and growth varied in situ and investigated the environmental drivers of seeded spat success in the southern inshore Great Barrier Reef. After 10 months, variation in spat survival and size was greatest at the smallest spatial scale (1–2 m) (27 and 11% of variation, respectively), indicating the scale at which the main drivers of post‐settlement survival and growth are occurring. Crustose coralline algae (CCA) cover on seeding units prior to deployment was a significant driver of short‐ and long‐term spat survival (22% of variation). Survival of Acropora millepora and A. muricata spat did not differ according to benthic community variation. Increasing cover of branching Acropora corals was correlated with decreased survival and the size of Montipora aequituberculata spat, although CCA cover on plugs remained the most influential factor determining survival. Interspecific variation in spat survival and size and higher survival and size in the side‐facing orientation of the seeding units suggest natural variation in response to the seeding method, warranting further experiments to refine species selection and deployment methods prior to upscaling. High within‐site variation in seeded spat survival and size highlights the need for future studies of ecological factors driving post‐settlement mortality at fine spatial scales. [ABSTRACT FROM AUTHOR]

Guanosine Triphosphate (GTP)ases of Immunity Associated Proteins (GIMAP) are small G proteins that in vertebrates, regulate immunity, apoptosis, and autophagy. While previously thought to be limited to vertebrates and plants, this family of proteins was recently characterized in a diversity of dinoflagellates. However, information regarding the function of GIMAPs in dinoflagellates is lacking. Therefore, the goal of this study (conducted from March-November of 2022) was to assess the expression of GIMAPs in the cnidarian symbiont Breviolum minutum (formerly Symbiodinium minutum, referred to as Bm_GIMAPs) in response to low light (25 vs 8 μmol m−2 s−1 for 9 d), thermal stress (22 vs 28 °C for 48 h), and symbiotic state (cultured vs in hospite). These factors were selected due to their importance in the lifestyle of a photosynthetic symbiont and relevance to the ecologically important issue of coral bleaching. The results indicate Bm_GIMAP expression increased under both low light and elevated temperature, suggesting a role in the response to bleaching related stressors. Cultured B. minutum had lower baseline Bm_GIMAP expression than those in association with a cnidarian host, but a stronger response to thermal stress, suggesting their function is influenced by symbiosis. Lastly, further support for the responsiveness of GIMAPs to thermal stress was provided by a comparison with previously published RNA-seq data from cultured Symbiodiniaceae. Collectively, the results presented here represent the first functional investigation of GIMAPs in an ecologically important group of protists and provide a greater understanding of the molecular response of dinoflagellates to stressors related to bleaching. [ABSTRACT FROM AUTHOR]

Coral calcification is critical for reef growth and highly dependent on environmental conditions. Yet, little is known about how corals calcify under sub-optimal conditions (e.g., turbid waters, high nutrients, sedimentation) or coral growth in understudied regions such as the Colombian Caribbean. We therefore assessed the calcification and linear extension rates of five coral species across an inshore-to-offshore gradient in the Colombian Caribbean. A suite of environmental variables (temperature, light intensity, visibility, pH, nutrients) measured during the rainy season (May – November 2022) demonstrated more sub-optimal conditions inshore compared to offshore. Across all species, calcification rates were 59% and 37% lower inshore compared to the offshore and midshore sites, respectively. Across all sites, massive corals calcified up to 92% more than branching species but were more susceptible to heat stress and sub-optimal inshore conditions. However, branching species had reduced survival due to extreme climatic events (i.e., bleaching, hurricanes). A comparison with published rates for the wider Caribbean revealed that massive species in the Colombian Caribbean grow up to 11 times more than those in the wider Caribbean while branching species generally have similar growth rates, but this finding may have been influenced by fragment size and/or heat stress. Our findings indicate that present-day environmental conditions, coupled with more frequent extreme climatic events, will favor massive over branching species in midshore areas of the Colombian Caribbean. This suggests a possible shift towards faster calcifying massive species in future coral communities, possibly exacerbating the ongoing regional decline in branching species over the last decades. [ABSTRACT FROM AUTHOR]

The impacts of (repeat) bleaching events and the differential heat stress susceptibility of hard coral taxa are largely unknown in Malaysia, although it is part of the greater coral triangle. Here we determined bleaching trajectories of 46 hard coral taxa across- and within-reef scales based on data recorded during the first reported back-to-back coral bleaching occurrences in Malaysia between May 2019 and September 2020. Although the severity of coral bleaching in both years did not correspond to the rather small magnitude of heat stress observed, i.e., Degree Heating Weeks (DHW) of 1.05 °C-weeks and 0 °C-weeks in 2019 and 2020 respectively, we observed high levels of bleaching (55.21% and 26.63% of all surveyed colonies in 2019 and 2020, respectively). Notably, the bleaching response for both consecutive years was highly taxon-specific and significantly varied across- and within-reef scales. Mortality rates overall were low following the 2019 event, likely due to a rapid decrease in heat stress. Five of the 46 surveyed hard coral taxa exhibited more severe bleaching in 2020, despite a lower heat stress load. Interestingly, we observed low bleaching of ascribed susceptible taxa such as Acropora and Montipora, while we found taxa considered to be resilient, e.g. Heliopora and Porites, to exhibit severe bleaching, suggesting a reversal of bleaching hierarchies of taxa over time. Our findings provide a foundation for further coral bleaching studies in a region with few published records to enable more accurate regional assessments and to follow the trajectory of future coral bleaching events. [ABSTRACT FROM AUTHOR]

Understanding and preserving the deep sea ecosystems is paramount for marine conservation efforts. Automated object (deep-sea biota) classification can enable the creation of detailed habitat maps that not only aid in biodiversity assessments but also provide essential data to evaluate ecosystem health and resilience. Having a significant source of labelled data helps prevent overfitting and enables training deep learning models with numerous parameters. In this paper, we contribute to the establishment of a significant deep-sea remotely operated vehicle (ROV) image classification dataset with 3994 images featuring deep-sea biota belonging to 33 classes. We manually label the images through rigorous quality control with human-in-the-loop image labelling. Leveraging data from ROV equipped with advanced imaging systems, our study provides results using novel deep-learning models for image classification. We use deep learning models including ResNet, DenseNet, Inception, and Inception-ResNet to benchmark the dataset that features class imbalance with many classes. Our results show that the Inception-ResNet model provides a mean classification accuracy of 65%, with AUC scores exceeding 0.8 for each class. [ABSTRACT FROM AUTHOR]

Background: Low oxygen in marine environments, intensified by climate change and local pollution, poses a substantial threat to global marine ecosystems, especially impacting vulnerable coral reefs and causing metabolic crises and bleaching-induced mortality. Yet, our understanding of the potential impacts in tropical regions is incomplete. Furthermore, uncertainty surrounds the physiological responses of corals to hypoxia and anoxia conditions. Methods: We initially monitored in situ dissolved oxygen (DO) levels at Kham Island in the lower Gulf of Thailand. Subsequently, we conducted a 72-hour experimental exposure of corals with different morphologies—Pocillopora acuta, Porites lutea, and Turbinaria mesenterina—to low oxygen conditions, while following a 12/12-hour dark/light cycle. Three distinct DO conditions were employed: ambient (DO 6.0 ± 0.5 mg L−1), hypoxia (DO 2.0 ± 0.5 mg L−1), and anoxia (DO < 0.5 mg L−1). We measured and compared photosynthetic efficiency, Symbiodiniaceae density, chlorophyll concentration, respiratory rates, primary production, and calcification across the various treatments. Results: Persistent hypoxia was observed at the study site. Subsequent experiments revealed that low oxygen levels led to a notable decrease in the maximum quantum yield over time in all the species tested, accompanied by declining rates of respiration and calcification. Our findings reveal the sensitivity of corals to both hypoxia and anoxia, particularly affecting processes crucial to energy balance and structural integrity. Notably, P. lutea and T. mesenterina exhibited no mortality over the 72-hour period under hypoxia and anoxia conditions, while P. acuta, exposed to anoxia, experienced mortality with tissue loss within 24 hours. This study underscores species-specific variations in susceptibility associated with different morphologies under low oxygen conditions. The results demonstrate the substantial impact of deoxygenation on coral growth and health, with the compounded challenges of climate change and coastal pollution exacerbating oxygen availability, leading to increasingly significant implications for coral ecosystems. [ABSTRACT FROM AUTHOR]