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Effective treatment and prevention of any disease necessitates knowledge of the causative agent, yet the causative agents of most coral diseases remain unknown, in part due to the difficulty of distinguishing the pathogenic microbe(s) among the complex microbial backdrop of coral hosts. Stony coral tissue loss disease (SCTLD) is a particularly destructive disease of unknown etiology, capable of transmitting through the water column and killing entire colonies within a matter of weeks. Here we used a previously described method to (i) isolate diseased and apparently healthy coral colonies within individual mesocosms containing filtered seawater with low microbial background levels; (ii) incubate for several days to enrich the water with coral-shed microbes; (iii) use tangential-flow filtration to concentrate the microbial community in the mesocosm water; and then (iv) filter the resulting concentrate through a sequential series of different pore-sized filters. To investigate the size class of microorganism(s) associated with SCTLD transmission, we used 0.8 µm pore size filters to capture microeukaryotes and expelled zooxanthellae, 0.22 µm pore size filters to capture bacteria and large viruses, and 0.025 µm pore size filters to capture smaller viruses. In an attempt to further refine which size fraction(s) contained the transmissible element of SCTLD, we then applied these filters to healthy "receiver" coral fragments and monitored them for the onset of SCTLD signs over three separate experimental runs. However, several factors outside of our control confounded the transmission results, rendering them inconclusive. As the bulk of prior studies of SCTLD in coral tissues have primarily investigated the associated bacterial community, we chose to characterize the prokaryotic community associated with all mesocosm 0.22 µm pore size filters using Illumina sequencing of the V4 region of the 16S rRNA gene. We identified overlaps with prior SCTLD studies, including the presence of numerous previously identified SCTLD bioindicators within our mesocosms. The identification in our mesocosms of specific bacterial amplicon sequence variants that also appear across prior studies spanning different collection years, geographic regions, source material, and coral species, suggests that bacteria may play some role in the disease. [ABSTRACT FROM AUTHOR]

Coral reef productivity depends on nutrient supply, mediated partly by enzymatic breakdown of organic matter. Alkaline phosphatases hydrolyse phosphomonoesters and are one of the key enzymes involved in marine phosphorus cycling. They are expressed by many marine organisms including planktonic microbes and metazoans such as corals, often in response to phosphate limitation, and are potentially important for coral P nutrition and reef biogeochemical cycling. However, most alkaline phosphatase activity (APA) data are from open-ocean environments, and the rates and drivers of APA in coastal waters are not well understood. Here, we measured both bulk seawater APA and the extracellular APA of three coral species at reefs in Singapore, where the monsoonal ocean current reversal creates strong seasonal changes in dissolved nutrient availability. Seawater APA was always measurable, averaging 9 ± 10 nmol l−1 h−1, but was not correlated with dissolved phosphate or other biogeochemical parameters. Experimental phosphate addition did not reduce seawater APA but addition of labile organic carbon increased seawater APA, indicating that seawater APA was driven by heterotrophic activity rather than phosphate stress. Coral APA ranged from 12 to 163 µmol m−2 h−1 depending on species, which was equivalent to the seawater APA in several metres of the overlying water column. While most coral APA was associated with the coral holobiont rather than the coral mucus, the mucus release added 13–56 µmol m−2 h−1 of APA into the water column, suggesting that corals can potentially contribute significantly to seawater APA. [ABSTRACT FROM AUTHOR]

Ocean warming is increasingly affecting marine ecosystems across the globe. Reef‐building corals are particularly affected by warming, with mass bleaching events increasing in frequency and leading to widespread coral mortality. Yet, some corals can resist or recover from bleaching better than others. Such variability in thermal resilience could be critical to reef persistence; however, the scientific community lacks standardized diagnostic approaches to rapidly and comparatively assess coral thermal vulnerability prior to bleaching events. We present the Coral Bleaching Automated Stress System (CBASS) as a low‐cost, open‐source, field‐portable experimental system for rapid empirical assessment of coral thermal thresholds using standardized temperature stress profiles and diagnostics. The CBASS consists of four or eight flow‐through experimental aquaria with independent water masses, lighting, and individual automated temperature controls capable of delivering custom modulating thermal profiles. The CBASS is used to conduct daily thermal stress exposures that typically include 3‐h temperature ramps to multiple target temperatures, a 3‐h hold period at the target temperatures, and a 1‐h ramp back down to ambient temperature, followed by an overnight recovery period. This mimics shallow water temperature profiles observed in coral reefs and prompts a rapid acute heat stress response that can serve as a diagnostic tool to identify putative thermotolerant corals for in‐depth assessments of adaptation mechanisms, targeted conservation, and possible use in restoration efforts. The CBASS is deployable within hours and can assay up to 40 coral fragments/aquaria/day, enabling high‐throughput, rapid determination of thermal thresholds for individual genotypes, populations, species, and sites using a standardized experimental framework. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Agricultural Sciences is the property of South China Agricultural University, Guangdong Academy of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coral reefs are one of the most biodiverse and productive ecosystems on Earth, and color has been shown to indicate coral health in Australian and Hawaiian reef systems. However, no standardized method exists to quantify coral health for Caribbean corals. Therefore, a health assessment card using coral color was developed for five species of Caribbean corals to monitor coral health non-invasively. To quantify coral health, individual corals of each species were photographed in a controlled environment to develop color profiles. Simultaneously, nondestructive measurements of "health" were quantified by measuring photosynthetic efficiency (Fv/Fm) using pulse amplitude modulation (PAM) fluorometry, which determines how efficiently the symbiotic algae provides energy to the coral host. The results of this work successfully corresponded photosynthetic efficiency to coral color for five dominant species of Caribbean corals to develop a Coral Health Assessment Card for Caribbean reefs. Implementing a standardized assessment of symbiont performance can assist in monitoring changes in coral health, which can consequently be implemented into long-term and widespread monitoring projects to track overall Caribbean reef health. [ABSTRACT FROM AUTHOR]

Ocean warming and marine heatwaves induced by climate change are impacting coral reefs globally, leading to coral bleaching and mortality. Yet, coral resistance and resilience to warming are not uniform across reef sites and corals can show inter- and intraspecific variability. To understand changes in coral health and to elucidate mechanisms of coral thermal tolerance, baseline data on the dynamics of coral holobiont performance under non-stressed conditions are needed. We monitored the seasonal dynamics of algal symbionts (family Symbiodiniaceae) hosted by corals from a chronically warmed and thermally variable reef compared to a thermally stable reef in southern Taiwan over 15 months. We assessed the genera and photochemical efficiency of Symbiodiniaceae in three coral species: Acropora nana, Pocillopora acuta, and Porites lutea. Both Durusdinium and Cladocopium were present in all coral species at both reef sites across all seasons, but general trends in their detection (based on qPCR cycle) varied between sites and among species. Photochemical efficiency (i.e., maximum quantum yield; Fv/Fm) was relatively similar between reef sites but differed consistently among species; no clear evidence of seasonal trends in Fv/Fm was found. Quantifying natural Symbiodiniaceae dynamics can help facilitate a more comprehensive interpretation of thermal tolerance response as well as plasticity potential of the coral holobiont. [ABSTRACT FROM AUTHOR]

Mutualisms are prevalent in many ecosystems, yet little is known about how symbioses are affected by ecological pressures. Here, we show delayed recovery for 13 coral‐dwelling goby fishes (genus Gobiodon) compared with their host Acropora corals following four consecutive cyclones and heatwaves. While corals became twice as abundant in 3 years postdisturbances, gobies were only half as abundant relative to predisturbances and half of the goby species disappeared. Although gobies primarily occupied one coral species in greater abundance predisturbances, surviving goby species shifted hosts to newly abundant coral species when their previously occupied hosts became rare postdisturbances. As host specialization is key for goby fitness, shifting hosts may have negative fitness consequences for gobies and corals alike and affect their survival in response to environmental changes. Our study is an early sign that mutualistic partners may not recover similarly from multiple disturbances, and that goby host plasticity, while potentially detrimental, may be the only possibility for early recovery. [ABSTRACT FROM AUTHOR]

Copyright of Asian Journals of Ecotoxicology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Heat waves are causing declines in coral reefs globally. Coral thermal responses depend on multiple, interacting drivers, such as past thermal exposure, endosymbiont community composition, and host genotype. This makes the understanding of their relative roles in adaptive and/or plastic responses crucial for anticipating impacts of future warming. Here, we extracted DNA and RNA from 102 Pocillopora colonies collected from 32 sites on 11 islands across the Pacific Ocean to characterize host-photosymbiont fidelity and to investigate patterns of gene expression across a historical thermal gradient. We report high host-photosymbiont fidelity and show that coral and microalgal gene expression respond to different drivers. Differences in photosymbiotic association had only weak impacts on host gene expression, which was more strongly correlated with the historical thermal environment, whereas, photosymbiont gene expression was largely determined by microalgal lineage. Overall, our results reveal a three-tiered strategy of thermal acclimatization in Pocillopora underpinned by host-photosymbiont specificity, host transcriptomic plasticity, and differential photosymbiotic association under extreme warming. Using data from the Tara Pacific expedition to investigate symbiont fidelity and patterns of gene expression across a thermal gradient, this study shows that Pocillopora corals have a three-tiered strategy of thermal acclimatization that is underpinned by host–photosymbiont specificity, host transcriptomic plasticity, and differential photosymbiotic associations under extreme warming. [ABSTRACT FROM AUTHOR]

Parrotfish are key agents of bioerosion and sediment production in coral reef ecosystems; however, their dietary targets and therefore potential sources of variation in carbonate cycling lack resolution. Here we address this knowledge shortfall in our current understanding of parrotfish diets by testing the concept that protein-rich micro-photoautotrophs are the target prey for many Scarinine parrotfishes. We focus at fine spatial scales on the feeding substrata of 12 syntopic Indo-Pacific parrotfish species at mid-shelf sites around Lizard Island, Great Barrier Reef, Australia. We followed individual parrotfish on snorkel until biting was observed, and then extracted a reef core around each bite. The surface of each bite core was scraped to ~1 mm for quantitative microscopic analysis (up to 630 × magnification) and for 16S and 18S rRNA metabarcoding. The most dominant photoautotrophic group in terms of surface cover was filamentous cyanobacteria, followed by crustose coralline algae. Epiphytic, epilithic, endophytic and endolithic filamentous cyanobacteria were consistent bite core biota. Although the density of filamentous cyanobacteria on bite cores was largely consistent among the 12 parrotfish species, the quantitative microscopic data and rRNA metabarcoding revealed distinct differences between parrotfish species in the taxonomic composition of core biota. Our data provide further evidence that these syntopic parrotfish species partition feeding resources. [ABSTRACT FROM AUTHOR]

Coral reefs are iconic examples of climate change impacts because climate-induced heat stress causes the breakdown of the coral-algal symbiosis leading to a spectacular loss of color, termed 'coral bleaching'. To examine the fine-scale dynamics of this process, we re-sampled 600 individually marked Montipora capitata colonies from across Kāne'ohe Bay, Hawai'i and compared the algal symbiont composition before and after the 2019 bleaching event. The relative proportion of the heat-tolerant symbiont Durusdinium in corals increased in most parts of the bay following the bleaching event. Despite this widespread increase in abundance of Durusdinium, the overall algal symbiont community composition was largely unchanged, and hydrodynamically defined regions of the bay retained their distinct pre-bleaching compositions. We explain ~ 21% of the total variation, of which depth and temperature variability were the most significant environmental drivers of Symbiodiniaceae community composition by site regardless of bleaching intensity or change in relative proportion of Durusdinium. We hypothesize that the plasticity of symbiont composition in corals may be constrained to adaptively match the long-term environmental conditions surrounding the holobiont, despite an individual coral's stress and bleaching response. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is a severe threat to coral reefs mainly by reducing their calcification rate. Identifying the resilience factors of corals to decreasing seawater pH is of paramount importance to predict the survivability of coral reefs in the future. This study compared corals adapted to variable pHT (i.e., 7.23–8.06) from the semi‐enclosed lagoon of Bouraké, New Caledonia, to corals adapted to more stable seawater pHT (i.e., 7.90–8.18). In a 100‐day aquarium experiment, we examined the physiological response and genetic diversity of Symbiodiniaceae from three coral species (Acropora tenuis, Montipora digitata, and Porites sp.) from both sites under three stable pHNBS conditions (8.11, 7.76, 7.54) and one fluctuating pHNBS regime (between 7.56 and 8.07). Bouraké corals consistently exhibited higher growth rates than corals from the stable pH environment. Interestingly, A. tenuis from Bouraké showed the highest growth rate under the 7.76 pHNBS condition, whereas for M. digitata, and Porites sp. from Bouraké, growth was highest under the fluctuating regime and the 8.11 pHNBS conditions, respectively. While OA generally decreased coral calcification by ca. 16%, Bouraké corals showed higher growth rates than corals from the stable pH environment (21% increase for A. tenuis to 93% for M. digitata, with all pH conditions pooled). This superior performance coincided with divergent symbiont communities that were more homogenous for Bouraké corals. Corals adapted to variable pH conditions appear to have a better capacity to calcify under reduced pH compared to corals native to more stable pH condition. This response was not gained by corals from the more stable environment exposed to variable pH during the 100‐day experiment, suggesting that long‐term exposure to pH fluctuations and/or differences in symbiont communities benefit calcification under OA. [ABSTRACT FROM AUTHOR]

Global habitat degradation heightens the need to better understand patterns of genetic connectivity and diversity of marine biota across geographical ranges to guide conservation efforts. Corals across the Red Sea are subject to pronounced environmental differences, but studies so far suggest that animal populations are largely connected, excepting evidence for a genetic break between the northern‐central and southern regions. Here, we investigated population structure and holobiont assemblage of two common pocilloporid corals, Pocillopora verrucosa and Stylophora pistillata, across the Red Sea. We found little evidence for population differentiation in P. verrucosa, except for the southernmost site. Conversely, S. pistillata exhibited a complex population structure with evidence for within‐reef and regional genetic differentiation, in line with differences in their reproductive mode (P. verrucosa is a broadcast spawner and S. pistillata is a brooder). Analysis for genomic loci under positive selection identified 85 sites (18 of which were in coding sequences) that distinguished the southern P. verrucosa population from the remainder of the Red Sea population. By comparison, we found 128 loci (24 of which were residing in coding sequences) in S. pistillata with evidence for local adaptation at various sites. Functional annotation of the underlying proteins revealed putative roles in the response to stress, lipid metabolism, transport, cytoskeletal rearrangement, and ciliary function (among others). Microbial assemblages of both coral species showed pervasive association with microalgal symbionts from the genus Symbiodinium (former clade A) and bacteria from the genus Endozoicomonas that exhibited significant differences according to host genotype and environment. The disparity of population genetic and holobiont assemblage patterns even between closely related species (family Pocilloporidae) highlights the need for multispecies investigations to better understand the role of the environment in shaping evolutionary trajectories. It further emphasizes the importance of networks of reef reserves to achieve conservation of genetic variants critical to the future survival of coral ecosystems. [ABSTRACT FROM AUTHOR]

Confronting a sustained coral reef conservation crisis, we need new opportunities to rethink how to protect areas successfully and efficiently in the face of a changing world. We studied the benthic community, including foraminifera, fish community, and genetic connectivity (SSRs and SNPs) of main reef-building corals, Orbicella faveolata and Agaricia undata, along a Non-Protected Area (NPA) reef tract in Barú peninsula, including some isolated banks, near Cartagena and the National Natural Park Corales del Rosario y San Bernando (NNP CRySB), Colombia. The fringing reef track is homogeneous in benthic components, including algae, sponges, and foraminifera between all the studied sites, while corals exhibited differences between sites and depth ranges. Many reef sites sustain between 42.8 and 53% coral cover, which are among the highest recorded in this region, even higher than the nearby NNP. A total of 82 fish species were found, and the Foram Index-FI varies between 2 and 2.5, showing environmental conditions marginal for reef growth. The Barú NPA reef system can be considered spatial refugia under climate change and Anthropocene conditions, including resilient reefs at the mouth of Cartagena Bay (Magdalena River), a place of increased stressing factors. The admixture between NPA and NNP populations, the high coral cover in the NPA, the fish density and composition, the uniqueness of the diapiric banks, and the disturbance resistance are major arguments to protect this reef tract. We suggest designing a co-management scheme to ensure species connectivity, avoid further degradation, and involve different stakeholders. [ABSTRACT FROM AUTHOR]

Worldwide decline in coral populations has led to the development of numerous coral conservation and restoration groups. These groups have established successful methods for propagating and growing corals in nurseries for outplanting to degraded reefs. However, the environment within land-based nurseries differs from natural reef environments since nursery conditions are optimized to aid coral health and accelerate growth. This study compares the physiological condition of Mote Marine Laboratory's land-based nursery corals to over two decades of coral physiology data collected seasonally from wild conspecific populations of the Florida Keys. Coral metabolism metrics suggest that nursery corals are similar to wild conspecifics. Despite this, coral biomass and symbiotic algae pigmentation suggest that Mote's land-based nursery corals are acclimated to low light, and maintain different Symbiodiniaceae populations compared to wild conspecifics. Our findings elucidate how the biology and physiology of corals raised in land-based nurseries are different from wild coral populations and indicate nursery corals likely incur substantial photoacclimation processes during outplanting. These insights provide a physiological framework for coral conservation and management efforts that can be used when considering the condition of nursery-raised corals before outplanting to a reef. [ABSTRACT FROM AUTHOR]

Aim: The symbioses between corals and endosymbiotic dinoflagellates have been described as a flexible relationship whose dynamics could serve as a source of resilience for coral reef ecosystems. However, the factors that drive the establishment and maintenance of this co‐evolutionary relationship remain unclear. We examined the environmental and geographical factors structuring dinoflagellate communities in a wide‐ranging Indo‐Pacific coral to begin to address this gap. Location: Djibouti, Oman, Taiwan and French Polynesia. Taxon: Cauliflower corals (Pocillopora spp.), dinoflagellates (family Symbiodiniaceae). Methods: We analysed publicly available amplicon sequence data from the nuclear ribosomal DNA internal transcribed spacer 2, originating from Pocillopora spp. We also compiled environmental data such as sea surface temperature (SST) and time since the last local mass bleaching event. We ran generalized least squares models, PERMANOVAs and indicator species analyses, to understand how thermal regimes and geographical distances impacted Pocillopora spp.'s Symbiodiniaceae community composition. Results: Sea surface temperature was the most important factor driving Symbiodiniaceae community differences, with the largest effect size of the statistically significant factors. When focusing on individual Symbiodiniaceae genera, SST was likewise the most important factor. Our indicator species analyses revealed that specimens that had recently bleached were characterized by roughly equal proportions of Cladocopium spp. and Durusdinium spp., while specimens that had not recently bleached had a similar proportion of Durusdinium spp. as those that had recently bleached, but also showed a reduction in Cladocopium spp., with this deficiency made up by the presence of Symbiodinium spp. Main Conclusions: We provide further support for the hypothesis that coral's Symbiodiniaceae communities could facilitate host resilience to thermal stress. Our work is in direct conversation with a larger body of biogeography literature that highlights how local environmental regimes can impact contemporary population structure, even in marine taxa with widespread distributions. [ABSTRACT FROM AUTHOR]

Background: Tropical coral reefs cover only ca. 0.1% of the Earth's surface but harbour exceptional marine biodiversity and provide vital ecosystem services to millions of people living nearby. They are currently threatened by global (e.g. climate change) and local (e.g. chemical pollution) stressors that interact in multiple ways. While global stressors cannot be mitigated by local actions alone, local stressors can be reduced through ecosystem management. Here, we aimed to systematically review experimental studies assessing the toxicity of chemical pollutants to tropical reef-building corals to generate accessible and usable knowledge and data that can be used to calculate measurement endpoints in ecological risk assessment. From the quantitative estimates of effects, we determined toxicity thresholds as the highest exposures tested at which no statistically significant adverse effects were observed, and we compared them to regulatory predicted no effect concentrations for the protection of marine organisms, to assess whether these reference values are indeed protective of corals. Methods: The evidence was taken from a systematic map of the impacts of chemicals arising from human activity on tropical reef-building corals published in 2021. All studies in the map database corresponding to the knowledge cluster "Evidence on the ecotoxicological effects of chemicals on corals" were selected. To identify subsequently published literature, the search was updated using a subset of the search string used for the systematic map. Titles, abstracts and full-texts were screened according to the criteria defining the selected cluster of the map. Because the eligibility criteria for the systematic review are narrower than the criteria used to define the cluster in the systematic map, additional screening was performed. Studies included were critically appraised and each study was rated as low, unclear, medium, or high risk of bias. Data were extracted from the studies and synthesised according to a strategy dependent on the type of exposure and outcome. Review findings: The systematic review reports the known effects of chemical exposures on corals from 847 studies corresponding to 181 articles. A total of 697 studies (161 articles) were included in the quantitative synthesis and 150 studies (50 articles) in the narrative synthesis of the findings. The quantitative synthesis records the effects of 2706 exposure concentrations-durations of 164 chemicals or mixtures of chemicals, and identifies 105 toxicity thresholds corresponding to 56 chemicals or mixtures of chemicals. When toxicity thresholds were compared to reference values set for the protection of marine organisms by environmental agencies, the reference values appear to be protective of corals for all but three chemicals assessed: the metal copper and the pesticides diuron and irgarol 1051. Conclusions: This open-access database of known ecotoxicological effects of chemical exposures on corals can assist managers in the ecological risk assessment of chemicals, by allowing easy determination of various ecotoxicological thresholds. Several limitations of the toxicity tests synthesised here were noted (in particular the lack of measurement of effective concentrations for more than half of the studies). Overall, most of the currently available data on coral toxicity should be replicated independently and extended to corals from less studied geographical regions and functional groups. [ABSTRACT FROM AUTHOR]

Coral reefs in Southeast Asia are becoming progressively degraded due to the natural and anthropogenic disturbances which lead to poor water quality threatening the reefs' health. Coral disease is one of the threats to the coral reefs worldwide but research on coral disease in Southeast Asia is relatively scarce especially on bacterial community associated with the disease. The destructive coral black band disease (BBD) can be found widely in the southern region of the South China Sea, Malaysia. This study aims to compare the microbial communities of healthy and BBD-infected coral tissue from two different coral species Montipora turtlensis and Acropora spicifera collected at the Shark Point of Pulau Redang, Terengganu. The bacterial isolated from corals nubbins were examined by combining culture-dependent method and bacterial sequencing of 16S rDNA. A total of 18 bacteria isolates were identified from both species of coral tissue samples prior to sub-culturing colonies samples. The sequences detected were derived from a wide taxonomic range, including representatives of Actinobacteria, Furmicutes and Proteobacteria phyla. Bacteria belonging to the phyla Proteobacteria were further divided into alpha and gammaproteobacteria. Most of the bacteria identified can be found on healthy and BBD-affected coral tissue samples; however, there are few bacteria which can be only found on BBD-affected tissue of respective coral species such as Lelliottia sp., Salnicola salarius and Microbacterium petrolearium for M. turtlensis while Pseudomonas stutzeri and Erythrobacter sp. for A. spicifera. [ABSTRACT FROM AUTHOR]

Aim: The aims were to test the role of temperature in latitudinal patterns of egg size and investigate maternal investment trade‐offs among coral taxa. Location: Global, from 34° S to 34° N. Time period: 1981–2020. Major taxa studied: Reef coral species from the order Scleractinia. Methods: We compiled a comprehensive geo‐referenced global dataset of egg sizes (diameter or volume) and fecundity (number of eggs per area) for colonial corals (Scleractinia; 123 species, 5359 observations and 39 localities), substantially enhanced by new field collections (>88% of observations). We used Bayesian phylogenetic multilevel models to test for Rass' rule (a hypothesized negative relationship between egg size and temperature); we also included other environmental variables and life history traits. We also tested whether a trade‐off exists between egg size and fecundity in broadcast spawning hermaphroditic corals with horizontal symbiont transmission (HHT). Results: We found a significant relationship between coral egg size and symbiont transmission. Eggs from coral species with vertical symbiont transmission were c. 18.8% smaller than those from species with horizontal symbiont transmission. We also found non‐significant relationships between egg size and sea surface temperature (SST) for broadcast spawning corals and between egg size and fecundity specifically for HHT species. Main conclusions: Contrary to recognized latitudinal patterns of egg size across taxa, our study does not provide support for Rass' rule in corals. Additionally, our findings do not support a maternal investment trade‐off between egg size and fecundity for HHT species. Our study used a phylogenetic framework that should be a standard practice when studying interspecific variation, including investigation of maternal investment and identification of the influence of multiple predictors on larval fitness (egg size), in addition to trade‐offs affecting propagule influx (fecundity). Both these functional traits are vital and have direct consequences for population maintenance and connectivity in sessile organisms, such as corals. [ABSTRACT FROM AUTHOR]

Context: Coral reef resilience is the product of multiple interacting processes that occur across various interacting scales. This complexity presents challenges for identifying solutions to the ongoing worldwide decline of coral reef ecosystems that are threatened by both local and global human stressors. Objectives: We highlight how coral reef resilience is studied at spatial, temporal, and functional scales, and explore emerging technologies that are bringing new insights to our understanding of reef resilience. We then provide a framework for integrating insights across scales by using new and existing technological and analytical tools. We also discuss the implications of scale on both the ecological processes that lead to declines of reefs, and how we study those mechanisms. Methods: To illustrate, we present a case study from Kāneʻohe Bay, Hawaiʻi, USA, linking remotely sensed hyperspectral imagery to within-colony symbiont communities that show differential responses to stress. Results: In doing so, we transform the scale at which we can study coral resilience from a few individuals to entire ecosystems. Conclusions: Together, these perspectives guide best practices for designing management solutions that scale from individuals to ecosystems by integrating multiple levels of biological organization from cellular processes to global patterns of coral degradation and resilience. [ABSTRACT FROM AUTHOR]

Coral reef ecosystem, which is one of the most important marine ecosystems, is suffered from serious degradation due to climate change (such as global warming and ocean acidification) and human activities (such as overfishing, chemical pollution). Organic ultraviolet absorbents (OUVs) are a kind of emerging "pseudo-persistent" organic pollutants. Previous studies indicated that OUVs have an importantly negative influence on coral health and are ubiquitous in various coral reef regions. To systematically understand the toxicity mechanism and ecological risk of OUVs to corals, this paper reviewed the toxicological effects of OUVs on corals from the perspectives of toxicological experiment design and toxicological effect endpoint. The results show that OUVs are toxic to corals at individual, tissular and molecular levels, with the toxicological endpoints of lethality, bleaching, tentacle retraction, [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) enrichment and ocean warming both negatively affect hard corals, but studies on their combined effects on other reef organisms are scarce. Octocorals are likely to become key players in future reef communities, but they are still highly under-investigated with regard to their responses to global and local environmental changes. Thus, we evaluated the individual and combined effects of DOC enrichment (10, 20 and 40 mg L-1 DOC, added as glucose) and warming (stepwise from 26 to 32 °C) on the widespread Indo-Pacific gorgonian Pinnigorgia flava in a 45-day laboratory experiment. Oxygen fluxes (net photosynthesis and respiration), as well as Symbiodiniaceae cell density and coral growth were assessed. Our results highlight a differential ecophysiological response to DOC enrichment and warming as well as their combination. Individual DOC addition did not significantly affect oxygen fluxes nor Symbiodiniaceae cell density and growth, while warming significantly decreased photosynthesis rates and Symbiodiniaceae cell density. When DOC enrichment and warming were combined, no effect on P. flava oxygen fluxes was observed while growth responded to certain DOC conditions depending on the temperature. Our findings indicate that P. flava is insensitive to the individual effect of DOC enrichment, but not to warming and the two stressors combined. This suggests that, if temperature remains below certain thresholds, this gorgonian species may gain a competitive advantage over coral species that are reportedly more affected by DOC eutrophication. However, under the expected increasing temperature scenarios, it is also likely that this octocoral species will be negatively affected, with potential consequences on community structure. This study contributes to our understanding of the conditions that drive phase shift dynamics in coastal coral reef ecosystemds. [ABSTRACT FROM AUTHOR]

Reef-building corals owe their evolutionary success to their symbiosis with unicellular algae (Symbiodiniaceae). However, increasingly frequent heat waves lead to coral mass-bleaching events and pose a serious threat to the survival of reef ecosystems. Despite significant efforts, a mechanistic understanding of coral–algal symbiosis functioning, what leads to its breakdown and what can prevent it, remains incomplete. The main obstacles are low amenability of corals to experimental handling and, owing to its obligatory nature, the difficulties of manipulating the coral–algal association. Indeed, many studies on the symbiotic partnership are conducted on other cnidarian model organisms and their results may therefore not be fully transferable to tropical reef-building corals. Here, we identify the tropical stony coral species Galaxea fascicularis as a novel candidate coral model system. Individual polyps of this species can be separated, enabling highly replicated genotype studies, and are well suited to experimental investigation of the symbiosis as they can be easily and effectively rid of their algal symbionts (bleached). We show that bleached adult individuals can reestablish symbiosis with non-native symbionts, and we report the completion of the gametogenic cycle ex situ, with the successful spawning in aquaria over multiple years. These achievements help overcome several of the major limitations to direct research on corals and highlight the potential of G. fascicularis as an important new model system for investigations of symbiosis functioning and manipulation. [ABSTRACT FROM AUTHOR]

Coral-associated microbial symbionts, particularly dinoflagellates from the family Symbiodiniaceae, play a significant role in corals' ability to survive and recover from marine heatwaves and mass bleaching events. Yet, there remain limited data on the extent to which microalgal endosymbiont associations shift in situ during and after prolonged heat stress and over small spatial scales, potentially limiting the alteration of symbiont communities as a restoration tool. In 2019, Mo'orea, French Polynesia experienced a massive thermal anomaly accompanied by widespread coral bleaching and mortality. Using ITS2 amplicon sequencing, we assessed the possibility of microalgal assemblages explaining the observed variability in Acropora hyacinthus thermal tolerance and recovery dynamics between reef habitats. Our data reveal flexibility in A. hyacinthus symbiont associations, but show that these associations were strongly linked to both heat stress response and the reef habitat in which the colony resided, indicating a prominent role of local environments in shaping in hospite symbiont communities and, consequently, holobiont thermal tolerance. Notably, bleaching resistant colonies were invariably dominated by Symbiodinium during and after the bleaching event. Although we did not detect temporal changes in symbiont communities during recovery from thermal stress, this novel observation of A. hyacinthus in association with Symbiodinium suggests that heat stress may have facilitated a shift. Further, we identify symbiont type profiles that are potentially diagnostic of bleaching susceptibility. Our findings illuminate the extent of symbiont flexibility for this species and location, with important implications for coral reef recovery and management in a rapidly changing ocean. [ABSTRACT FROM AUTHOR]

Summer upwelling areas may serve as a thermal refuge for coral reefs under climate change, and the environmental adaptation of scleractinian coral to upwelling environments remains to be further understood. In this work, we systematically analyzed how the coral holobionts of Galaxea fascicularis respond to different environments between the Qiongdong upwelling and non‐upwelling regions. The presence of colder and more saline water was found in seasonal upwelling region east of Hainan Island. Compared with the corals in the non‐upwelling environment, the corals from the upwelling environment generally had higher Symbiodiniaceae density, tissue biomass, and protein content. Evident spatial differences existed in Symbiodiniaceae composition among different regions, and the corals in the upwelling region had remarkably higher symbiont diversity. Importantly, the coastal upwelling under anthropogenic influence (i.e., nutrient pollution and coastal development) shaped coral bacterial communities significantly and decreased their diversity. Local adaptations of coral to environmental changes can be inferred from the flexibility and ecological functions of the coral core microbiome. In particular, the coastal upwelling environment led assembly of coral‐associated bacteria more deterministic rather than stochastic. In the upwelling region, microbial co‐occurrences had more positive interactions but the ecological network structure had a lower stability. These findings deepen the understanding of the ecological impact of upwelling on coral adaptation in the Anthropocene. Plain Language Summary: With the progress of global climate change, the frequency and severity of coral bleaching are expected to increase significantly. Fortunately, upwelling exposes corals to cool and nutrient‐rich waters, thereby helping to reduce the thermal impacts of climate change and serving as a potential thermal refuge. We investigated and sampled in coral reefs with different environmental gradients, including upwelling and non‐upwelling in Hainan Island. The Galaxea fascicularis samples from the upwelling region exhibited better coral physiological parameters (higher values of Symbiodiniaceae density, tissue biomass, and protein content). In addition, upwelling changed the diversity and structure of the coral microbiota (microalgal endosymbionts and bacteria) significantly. Coral hosts could act as filters for microorganisms, allowing certain microbial taxa to colonize or persist and selecting the most favorable and beneficial microbiome in a specific environment. Upwelling habitats might promote positive cooperation and simple interaction between bacterial communities associated with the coral host, which is crucial for the acclimatization of the holobiont to quickly respond to environmental changes. This study provides detailed analysis of how coral responds to the summer upwelling environment from a microbial perspective. Key Points: Galaxea fascicularis in upwelling under anthropogenic influence suggested high physiological plasticity and symbiont specificityMicrobiome flexibility facilitated local acclimatization of coral holobiont by readily responding to the upwelling environmentUpwelling promoted bacterial assembly more deterministic, but reduced the complexity and stability of the microbial network [ABSTRACT FROM AUTHOR]

Genomic studies are uncovering extensive cryptic diversity within reef‐building corals, suggesting that evolutionarily and ecologically relevant diversity is highly underestimated in the very organisms that structure coral reefs. Furthermore, endosymbiotic algae within coral host species can confer adaptive responses to environmental stress and may represent additional axes of coral genetic variation that are not constrained by taxonomic divergence of the cnidarian host. Here, we examine genetic variation in a common and widespread, reef‐building coral, Acropora tenuis, and its associated endosymbiotic algae along the entire expanse of the Great Barrier Reef (GBR). We use SNPs derived from genome‐wide sequencing to characterize the cnidarian coral host and organelles from zooxanthellate endosymbionts (genus Cladocopium). We discover three distinct and sympatric genetic clusters of coral hosts, whose distributions appear associated with latitude and inshore–offshore reef position. Demographic modelling suggests that the divergence history of the three distinct host taxa ranges from 0.5 to 1.5 million years ago, preceding the GBR's formation, and has been characterized by low‐to‐moderate ongoing inter‐taxon gene flow, consistent with occasional hybridization and introgression typifying coral evolution. Despite this differentiation in the cnidarian host, A. tenuis taxa share a common symbiont pool, dominated by the genus Cladocopium (Clade C). Cladocopium plastid diversity is not strongly associated with host identity but varies with reef location relative to shore: inshore colonies contain lower symbiont diversity on average but have greater differences between colonies as compared with symbiont communities from offshore colonies. Spatial genetic patterns of symbiont communities could reflect local selective pressures maintaining coral holobiont differentiation across an inshore–offshore environmental gradient. The strong influence of environment (but not host identity) on symbiont community composition supports the notion that symbiont community composition responds to habitat and may assist in the adaptation of corals to future environmental change. [ABSTRACT FROM AUTHOR]

By the century's end, many tropical seas will reach temperatures exceeding most coral species' thermal tolerance on an annual basis. The persistence of corals in these regions will, therefore, depend on their abilities to tolerate recurrent thermal stress. Although ecologists have long recognized that positive interspecific interactions can ameliorate environmental stress to expand the realized niche of plants and animals, coral bleaching studies have largely overlooked how interactions with community members outside of the coral holobiont shape the bleaching response. Here, we subjected a common coral, Pocillopora grandis, to 10 days of thermal stress in aquaria with and without the damselfish Dascyllus flavicaudus (yellowtail dascyllus), which commonly shelter within these corals, to examine how interactions with damselfish impacted coral thermal tolerance. Corals often benefit from nutrients excreted by animals they interact with and prior to thermal stress, corals grown with damselfish showed improved photophysiology (Fv/Fm) and developed larger endosymbiont populations. When exposed to thermal stress, corals with fish performed as well as control corals maintained at ambient temperatures without fish. In contrast, corals exposed to thermal stress without fish experienced photophysiological impairment, a more than 50% decline in endosymbiont density, and a 36% decrease in tissue protein content. At the end of the experiment, thermal stress caused average calcification rates to decrease by over 80% when damselfish were absent but increase nearly 25% when damselfish were present. Our study indicates that damselfish‐derived nutrients can increase coral thermal tolerance and are consistent with the Stress Gradient Hypothesis, which predicts that positive interactions become increasingly important for structuring communities as environmental stress increases. Because warming of just a few degrees can exceed corals' temperature tolerance to trigger bleaching and mortality, positive interactions could play a critical role in maintaining some coral species in warming regions until climate change is aggressively addressed. [ABSTRACT FROM AUTHOR]

Coral reefs worldwide are at risk due to climate change. Coral bleaching is becoming increasingly common and corals that survive bleaching events can suffer from temporary reproductive failure for several years. While water temperature is a key driver in causing coral bleaching, other environmental factors are involved, such as solar radiation. We investigated the individual and combined effects of temperature, photosynthetically active radiation (PAR), and ultraviolet radiation (UVR) on the spawning patterns and reproductive physiology of the Hawaiian mushroom coral Lobactis scutaria, using long-term experiments in aquaria. We examined effects on spawning timing, fertilisation success, and gamete physiology. Both warmer temperatures and filtering UVR altered the timing of spawning. Warmer temperatures caused a drop in fertilisation success. Warmer temperatures and higher PAR both negatively affected sperm and egg physiology. These results are concerning for the mushroom coral L. scutaria and similar reproductive data are urgently needed to predict future reproductive trends in other species. Nonetheless, thermal stress from global climate change will need to be adequately addressed to ensure the survival of reef-building corals in their natural environment throughout the next century and beyond. Until then, reproduction is likely to be increasingly impaired in a growing number of coral species. [ABSTRACT FROM AUTHOR]

Coral-associated bacteria play critical roles in the regulation of coral health and function. Environmental perturbations that alter the bacterial community structure can render the coral holobiont more susceptible and less resilient to disease. Understanding the natural variation of the coral microbiome across space and host species provides a baseline that can be used to distinguish shifts in community structure. Using a 16S rRNA gene metabarcoding approach, this study examines bacterial community structure across three scleractinian coral hosts. Our results show that corals of three regions—eastern and western Peninsular Malaysia and Singapore—host distinct bacterial communities; despite these differences, we were able to identify a core microbiome shared across all three species. This core microbiome was also present in samples previously collected in Thailand, suggesting that these core microbes play an important role in promoting and maintaining host health. For example, several have been identified as dimethylsulfoniopropionate (DMSP) metabolizers that have roles in sulfur cycling and the suppression of bacterial pathogens. Pachyseris speciosa has the most variable microbiome, followed by Porites lutea, with the composition of the Diploastrea heliopora microbiome the least variable throughout all locations. Microbial taxa associated with each region or site are likely shaped by local environmental conditions. Taken together, host identity is a major driver of differences in microbial community structure, while environmental heterogeneity shapes communities at finer scales. [ABSTRACT FROM AUTHOR]

For instance, in situ hybridization of coral tissue sections with probes targeting mRNAs showed that certain coral genes were only expressed in gastrodermal cells harbouring Symbiodiniaceae (Traylor-Knowles et al., [35]). Historically, coral research has had a strong microbiological focus because corals engage in symbioses not only with prokaryotes, viruses and fungi - microbes found in association with most animals - but also with unicellular photosymbionts in the family Symbiodiniaceae (Dinophyceae). However, the most common approach to study coral-associated microbes (e.g., genotyping, amplicon sequencing, or various omics techniques) involves the homogenization of coral fragments. [Extracted from the article]

The world's coral reef ecosystems are built by a symbiotic relationship between reef corals and the dinoflagellates of the family Symbiodiniaceae. Climate change has already impacted the world's coral reef ecosystems. Some corals can survive in extreme environmental conditions through the acquisition of stress-tolerant endosymbionts. In the present study, the genetic diversity of endosymbionts of fourteen coral genera such as Porites (Five), Favia (Two), and Acropora (Seven) sampled from the reefs of Mandapam and Rameswaram, Palk Bay, Tamil Nadu, India was assessed by sequencing both large (LSU) and small subunit (SSU) gene fragments. The phylogenetic construction of LSU revealed the diversity of thermo tolerant Clade D that was monophyletic throughout various coral taxa. Comparison of thermo tolerant clade D with SST (> 32 °C) has provided valid evidence for the presence of the endosymbiont Durusdinium sp. (Clade D) across different coral species in the Palk Bay. [ABSTRACT FROM AUTHOR]

Dinoflagellates are important components of marine ecosystems and essential coral symbionts, yet little is known about their genomes. We report here on the analysis of a high-quality assembly from the 1180-megabase genome of Symbiodinium kawagutii. We annotated protein-coding genes and identified Symbiodinium-specific gene families. No whole-genome duplication was observed, but instead we found active (retro) transposition and gene family expansion, especially in processes important for successful symbiosis with corals. We also documented genes potentially governing sexual reproduction and cyst formation, novel promoter elements, and a microRNA system potentially regulating gene expression in both symbiont and coral. We found biochemical complementarity between genomes of S. kawagutii and the anthozoan Acropora, indicative of host-symbiont coevolution, providing a resource for studying the molecular basis and evolution of coral symbiosis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pocillopora damicornis is more sensitive to cold than heat stress. • The coral symbionts shuffle under either heat or cold stress. • Inverse shuffling to thermo-sensitive Cladocopium is observed after recovery. • Symbiont shuffling is correlated with photodamage caused by temperature stress. • Symbiont shuffling facilitates host's resilience to temperature stress and recovery. Reef-building corals usually form a symbiotic relationship with various photosynthetic dinoflagellates, which may determine the physiology and stress tolerance of their hosts. The mechanisms governing symbiont dynamics are still poorly understood, but may be driven by temperature. Therefore, we performed indoor experiments to examine the photochemical efficiency and symbiont dynamics in the coral Pocillopora damicornis with thermo-sensitive Cladocopium (PdC) or thermo-tolerant Durusdinium (PdD) under 6-day temperature stress and after 90-day post-stress recovery. Regardless of the symbiont type, photochemical damage was induced by both heat and cold stress. We observed PdC with greater photodamage had a faster increase in the proportion of Durusdinium when exposed to heat or cold stress, whereas an inverse shuffling to Cladocopium in both PdC and PdD after the recovery period. This is the first record of symbiont shuffling from the originally dominant Durusdinium to Cladocopium in adult corals under laboratory conditions and the degree of symbiont shuffling was highly correlated with the photodamage. Overall, our findings suggest that symbiont shuffling can act as a critical mechanism allowing corals to rapidly adjust to environmental changes, which has implications for the capacity of corals to prevail in oceans with greater temperature fluctuations in the future. [ABSTRACT FROM AUTHOR]

Background: Endozoicomonas bacteria symbiosis with various marine organisms is hypothesized as a potential indicator of health in corals. Although many amplicon analyses using 16S rRNA gene have suggested the diversity of Endozoicomonas species, genome analysis has been limited due to contamination of host-derived sequences and difficulties in culture and metagenomic analysis. Therefore, the evolutionary and functional potential of individual Endozoicomonas species symbiotic with the same coral species remains unresolved. Results: In this study, we applied a novel single-cell genomics technique using droplet microfluidics to obtain single-cell amplified genomes (SAGs) for uncultured coral-associated Endozoicomonas spp. We obtained seven novel Endozoicomonas genomes and quantitative bacterial composition from Acropora tenuis corals at four sites in Japan. Our quantitative 16S rRNA gene and comparative genomic analysis revealed that these Endozoicomonas spp. belong to different lineages (Clade A and Clade B), with widely varying abundance among individual corals. Furthermore, each Endozoicomonas species possessed various eukaryotic-like genes in clade-specific genes. It was suggested that these eukaryotic-like genes might have a potential ability of different functions in each clade, such as infection of the host coral or suppression of host immune pathways. These Endozoicomonas species may have adopted different host adaptation strategies despite living symbiotically on the same coral. Conclusions: This study suggests that coral-associated Endozoicomonas spp. on the same species of coral have different evolutional strategies and functional potentials in each species and emphasizes the need to analyze the genome of each uncultured strain in future coral-Endozoicomonas relationships studies. BqfFwXzdNKfPeBMVktWjTu Video Abstract [ABSTRACT FROM AUTHOR]

Rising oceanic temperatures create more frequent coral bleaching events worldwide and as such there exists a need for rapid, non-destructive survey techniques to gather greater and higher definition information than that offered by traditional spectral based monitoring systems. Here, we examine thermally induced laboratory bleaching of Montipora capricornis and Montipora confusa samples, utilising hyperspectral data to gain an understanding of coral bleaching from a spectral standpoint. The data revealed several characteristic spectral peaks that can be used to make health determinations. The fluorescence peaks are attributed to fluorescent proteins (FPs) and Chlorophyll-a fluorescence. The reflectance peaks can be attributed to Chlorophyll absorption and accessory pigments such as Peridinin and Diadinoxanthin. Each characteristic spectral peak or 'marker' allows for observation of each aspect of coral health and hence, simultaneous monitoring of these markers using hyperspectral imaging techniques provides an opportunity to better understand the processes occurring during bleaching and the rates at which they occur relative to one another. [ABSTRACT FROM AUTHOR]

Coral growth is an important metric of coral health and underpins reef-scale functional attributes such as structural complexity and calcium carbonate production. There persists, however, a paucity of growth data for most reef-building regions, especially for coral species whose skeletal architecture prevents the use of traditional methods such as coring and Alizarin staining. We used structure-from-motion photogrammetry to quantify a range of colony-scale growth metrics for six coral species in the Mexican Caribbean and present a newly developed workflow to measure colony volume change over time. Our results provide the first growth metrics for two species that are now major space occupiers on Caribbean reefs, Agaricia agaricites and Agaricia tenuifolia. We also document higher linear extension, volume increase and calcification rates within back reef compared to fore reef environments for four other common species: Orbicella faveolata, Porites astreoides, Siderastrea siderea and Pseudodiploria strigosa. Linear extension rates in our study were lower than those obtained via computed tomography (CT) scans of coral cores from the same sites, as the photogrammetry method averages growth in all dimensions, while the CT method depicts growth only along the main growth axis (upwards). The comparison of direct volume change versus potential volume increase calculated from linear extension emphasizes the importance of assessing whole colony growth to improve calcification estimates. The method presented here provides an approach that can generate accurate calcification estimates alongside a range of other whole-colony growth metrics in a non-invasive way. [ABSTRACT FROM AUTHOR]

Global change and local stressors are simultaneously affecting the nearshore corals, and microbiome flexibility may assist corals in thriving under such multiple stressors. Here, we investigated the effects of various environmental variables on Galaxea fascicularis holobiont from nearshore and offshore reefs. These nearshore reefs were more turbid, eutrophic, and warm than offshore reefs. However, coral physiological parameters did not differ significantly. Corals under stressful nearshore environments had low symbiont diversity and selected more tolerant Symbiodiniaceae. The bacterial diversity of offshore corals was significantly higher, and their community composition varied obviously. Diffusion limitations and environmental heterogeneity were essential in structuring microbial communities. Functional annotation analysis demonstrated significant differences between nearshore and offshore corals in bacterial functional groups. Environmental stress significantly reduced the complexity and connectivity of bacterial networks, and the abundances of keystone taxa altered considerably. These results indicated that corals could thrive nearshore through holobiont plasticity to cope with multiple environmental stresses. [ABSTRACT FROM AUTHOR]

Background: Symbionts provide a variety of reproductive, nutritional, and defensive resources to their hosts, but those resources can vary depending on symbiont community composition. As genetic techniques open our eyes to the breadth of symbiont diversity within myriad microbiomes, symbiosis research has begun to consider what ecological mechanisms affect the identity and relative abundance of symbiont species and how this community structure impacts resource exchange among partners. Here, we manipulated the in hospite density and relative ratio of two species of coral endosymbionts (Symbiodinium microadriaticum and Breviolum minutum) and used stable isotope enrichment to trace nutrient exchange with the host, Briareum asbestinum. Results: The patterns of uptake and translocation of carbon and nitrogen varied with both density and ratio of symbionts. Once a density threshold was reached, carbon acquisition decreased with increasing proportions of S. microadriaticum. In hosts dominated by B. minutum, nitrogen uptake was density independent and intermediate. Conversely, for those corals dominated by S. microadriaticum, nitrogen uptake decreased as densities increased, and as a result, these hosts had the overall highest (at low density) and lowest (at high density) nitrogen enrichment. Conclusions: Our findings show that the uptake and sharing of nutrients was strongly dependent on both the density of symbionts within the host, as well as which symbiont species was dominant. Together, these complex interactive effects suggest that host regulation and the repression of in hospite symbiont competition can ultimately lead to a more productive mutualism. 7h9js9xm2ik2K7FmJ48qFB Video Abstract [ABSTRACT FROM AUTHOR]

Microbes play a key role in reef dynamics, mediating the competition between scleractinian corals and benthic algae; however, major shifts in bacterial communities among coral species in response to increases in the abundance of algae are not well understood. We investigated the taxonomic composition of coral-associated microbial communities under algae-overgrowth conditions using 16S rRNA gene sequencing. The results showed that non-algal (i.e., healthy) tissue (HH) had lower bacterial abundance and diversity than tissue collected from the coral–algae interface boundary (HA) and areas of algae growth (AA). Specifically, the HA and AA samples had higher relative abundances of Saprospiraceae, Rhodobacteraceae, and Alteromonadaceae. Compared with Platygyra sp. and Montipora sp., the physiological response of Pocillopora sp. was more intense under algae-induced stress based on microbial gene function prediction. Our results indicate that algal pressure can significantly alter the microbial community structure and function of coral ecosystems. Our data thus provide new insight into the relationship between corals and their microbiome under environmental stress. [ABSTRACT FROM AUTHOR]

Life-history strategies play a critical role in susceptibility to environmental stresses for Scleractinia coral. Metabolomics, which is capable of determining the metabolic responses of biological systems to genetic and environmental changes, is competent for the characterization of species' biological traits. In this study, two coral species (Pocillopora meandrina and Seriatopora hystrix in the South China Sea) with different life-history strategies ("competitive" and "weedy") were targeted, and untargeted mass spectrometry metabolomics combined with molecular networking was applied to characterize their differential metabolic pathways. The results show that lyso-platelet activating factors (lyso-PAFs), diacylglyceryl carboxyhydroxymethylcholine (DGCC), aromatic amino acids, and sulfhydryl compounds were more enriched in P. meandrina, whereas new phospholipids, dehydrated phosphoglycerol dihydroceramide (de-PG DHC), monoacylglycerol (MAG), fatty acids (FA) (C < 18), short peptides, and guanidine compounds were more enriched in S. hystrix. The metabolic pathways involved immune response, energy metabolism, cellular membrane structure regulation, oxidative stress system, secondary metabolite synthesis, etc. While the immune system (lysoPAF) and secondary metabolite synthesis (aromatic amino acids and sulfhydryl compounds) facilitates fast growth and resistance to environmental stressors of P. meandrina, the cell membrane structure (structural lipids), energy storage (storage lipids), oxidative stress system (short peptides), and secondary metabolite synthesis (guanidine compounds) are beneficial to the survival of S. hystrix in harsh conditions. This study contributes to the understanding of the potential molecular traits underlying life-history strategies of different coral species. [ABSTRACT FROM AUTHOR]

Interest is growing in developing conservation strategies to restore and maintain coral reef ecosystems in the face of mounting anthropogenic stressors, particularly climate warming and associated mass bleaching events. One such approach is to propagate coral colonies ex situ and transplant them to degraded reef areas to augment habitat for reef‐dependent fauna, prevent colonization from spatial competitors, and enhance coral reproductive output. In addition to such "demographic restoration" efforts, manipulating the thermal tolerance of outplanted colonies through assisted relocation, selective breeding, or genetic engineering is being considered for enhancing rates of evolutionary adaptation to warming. Although research into such "assisted evolution" strategies has been growing, their expected performance remains unclear. We evaluated the potential outcomes of demographic restoration and assisted evolution in climate change scenarios using an eco‐evolutionary simulation model. We found that supplementing reefs with pre‐existing genotypes (demographic restoration) offers little climate resilience benefits unless input levels are large and maintained for centuries. Supplementation with thermally resistant colonies was successful at improving coral cover at lower input levels, but only if maintained for at least a century. Overall, we found that, although demographic restoration and assisted evolution have the potential to improve long‐term coral cover, both approaches had a limited impact in preventing severe declines under climate change scenarios. Conversely, with sufficient natural genetic variance and time, corals could readily adapt to warming temperatures, suggesting that restoration approaches focused on building genetic variance may outperform those based solely on introducing heat‐tolerant genotypes. [ABSTRACT FROM AUTHOR]

The ecological success of tropical corals is regulated by symbiotic dinoflagellate algae (Symbiodiniaceae). Corals can associate with multiple Symbiodiniaceae species simultaneously, yet the conditions that permit Symbiodiniaceae cohabitation are not understood. We examined how corals self-shade their own tissues causing within-colony light gradients that drive Symbiodiniaceae photoacclimatory processes and positional genetic disparity. Paired light 'exposed' and 'shaded' samples from 20 coral species were collected from a shallow coral reef (Rarotonga, Cook Islands). Through active chlorophyll fluorometry, rapid light curves revealed that exposed Symbiodiniaceae exhibited 50% higher values in minimum saturating irradiances and demonstrated a shift towards preferential nonphotochemical quenching [1 – Q], consistent with higher overall light exposure. High-throughput or targeted DNA sequencing of ITS2 and psbAncr markers demonstrated that corals harboured distinct and/or differentially abundant Symbiodiniaceae ITS2 sequences (typically rare in relative abundance) or multiple ITS2 intragenomic variant profiles across shaded vs exposed regions. In Hydnophora cf. microconos, within-colony symbiont genetic disparity was positively correlated with the magnitude of difference in [1 – Q] utilisation. Together, these results suggest that within-colony light gradients produce distinct optical niches that enable symbiont cohabitation via photoadaptation, a phenomenon that is expected to increase the adaptive capacity of corals under future climates. [ABSTRACT FROM AUTHOR]

Niche differentiation is a key stabilizing mechanism in the maintenance of biodiversity and species coexistence. Recent work shows that trophic niche partitioning between parrotfishes (Labridae: Scarini) is more extensive than previously described. One Indo-Pacific species, Scarus spinus, appears highly specialized, scraping crustose coralline algae (CCA) with powerful oral jaws. CCA are of low nutritional value, suggesting that the dietary targets of this parrotfish are protein-rich microphotoautotrophs associated with CCA, particularly filamentous cyanobacteria. We collected feeding substrata samples at mid-shelf and outer-shelf sites near Lizard Island, Great Barrier Reef, Australia, in 2018 and 2019, respectively. Scarus spinus were followed on snorkel. When biting was observed, bite substrata were photographed and then a 22-mm-diameter core extracted around the bite site. Density of biota including filamentous cyanobacteria and diatoms was quantified microscopically on photographs of the bite cores (up to 630 × magnification). The taxonomy of cyanobacteria and CCA was refined using next-generation sequencing of 16S and 18S rRNA genes, respectively. CCA and filamentous cyanobacteria were present on all bite cores and the density of filamentous cyanobacteria where S. spinus fed did not vary between mid-shelf and outer-reef samples. Epiphytic and shallow endophytic cyanobacteria were consistently associated with the CCA where S. spinus fed, including Calothrix spp., Mastigocoleus testarum, Leptolyngbya spp., Hyella patelloides and Oscillatoriales. Our results emphasize the importance of high-resolution species-specific dietary data for parrotfishes. We conclude that polyphasic methods are essential both for diet tracing and to develop our understanding of the cyanobacteria that are integral to coral reef functioning. [ABSTRACT FROM AUTHOR]

In August to September 2020, severe sea surface temperature anomalies were recorded for Hainan Island and the Beibu Gulf from South China Sea (SCS) and at the same time an unprecedented mass coral event occurred there, spreading over the fringing reef along the Chinese mainland and around Hainan Island. Field surveys revealed that 81.08% of the 74 surveyed sites were bleached (average bleaching percentage 51.14%), exceeding the historical record for these areas. Percentage bleaching coincided with the cumulative time that corals were exposed to heat stress, as measured by Coral Reef Watch's satellite Degree Heating Week (DHW). Geographically, western Hainan Island and Weizhou Island incurred more severe bleaching (56.27%) than did eastern Hainan Island (1.26%) even at the same latitude. Intriguingly, a generalized linear model with a binomial error structure demonstrated that DHW was a significant positive predictor of bleaching with 50% bleaching probability at 16.61 °C-weeks which suggested a higher DHW bleaching threshold. A strong negative correlation between DHW and coral cover as well as diversity was found. Further, coral community based on species composition at surveyed sites was dominated by massive/encrusting taxa Goniopora and Porites with high level of bleaching and in contrast genus Acropora showed a strong resistance to heat stress compared with other coral taxa. The follow-up in situ surveys in 2021 revealed there was no loss of coral cover during last year mass bleaching event and falling bleaching percentage was surprisingly observed despite under same level of thermal stress. These results suggest both transformation of coral reef assemblages and coral acclimation may play an important role in resisting extreme heat condition in SCS. [ABSTRACT FROM AUTHOR]

We discuss observations of tidally varying wave‐forced flows in the reef system on Ofu, American Samoa, a barrier reef and lagoon system that appears open at low tide and closed at high tide. At high tide, the free‐surface pressure gradient nearly balances the radiation stress gradient in the depth‐integrated momentum equation. At depth, there is an imbalance between these two forces, generating an undertow and flows that turn alongshore, and for some of the time, offshore, behavior similar to rip currents observed on beaches. At low tides, the wave forcing drives purely onshore flows. In general, wave transport is important to determining the total net transport. While the dynamically closed nature of the lagoon mostly suppresses cross‐reef transport, there is always some flow through the lagoon with the strongest flows occurring at high tides and when the wave forcing is strongest. Plain Language Summary: Waves and flows observed in the coral reef lagoon system located on the south shore of Ofu, American Samoa, show that flows in the lagoon are driven by incident swell modulated by tidal variations in depth on the steep fore reef and on the shallow reef flat. At low tide, flows are across the reef flat from the fore reef to the lagoon behave as though the lagoon is open to the ocean, whereas at high tide, flows into the lagoon are strongly limited by the resistance felt by the flow out of the lagoon. As a consequence, flows on the reef flat can develop an undertow, as is seen on beaches, although this varies with position on the reef flat. Nonetheless, overall flows in the lagoon are strongest at high tides and weakest at low tides. Key Points: Wave driven flows and flow dynamics vary with tidal water levelCoral reef lagoon appears closed at high tide and open at low tideOffshore flows at some depths can develop at times when the lagoon is closed [ABSTRACT FROM AUTHOR]

Understanding the role of coral reefs on air‐sea CO2 exchange is essential to accurately estimate carbon budgets throughout the tropical and subtropical oceans. Results from research conducted in humid marine environments show coral reefs are mainly net sources of CO2 to the atmosphere due to calcification being dominant over respiration and dissolution. However, coral reefs are also found bordering deserts in the subtropical high‐pressure belt. Here, we present results from concurrent direct measurements of air‐sea CO2 exchange over fringing coral reefs and open sea bordered by hyper‐arid deserts in the Gulf of Eilat (Aqaba). The fringing coral reefs were found to be a net sink of CO2 at −1.62 ± 4 μmol m−2 s−1 sequestering 1.96 times more CO2 than adjacent open sea. The CO2 fluxes showed a negative correlation with some local meteorological parameters such as humidity, wind speed, and net radiation but were positively correlated to air temperature. The air‐sea CO2 fluxes were also found to be correlated with dust, which is believed to trigger metabolic processes in bacteria and phytoplankton in the low‐nutrient, low‐chlorophyll sea of the study site. Results are compared to measurements from the humid marine setting of the Great Barrier Reef, Australia. Plain Language Summary: Quantifying air‐sea exchange of CO2 is critical to developing accurate carbon budgets for the world oceans. However, uncertainty remains as to whether coral reefs are net sinks or sources of atmospheric CO2. Here we present direct measurements of air‐sea CO2 exchange over the desert fringing coral reefs in the northern Gulf of Eilat (Aqaba), Israel. Unlike coral reefs in humid tropical and subtropical locations, which have been found to be mainly net sources of CO2 to the atmosphere, our results indicate that the fringing coral reefs in the northern Gulf of Eilat (Aqaba) are net sinks of atmospheric CO2. This net influx of CO2 correlates with periods of increased dust concentrations in the atmosphere. The deposition of this dust into the low‐nutrient, low‐chlorophyll waters of the coral reef triggers an increase in metabolic processes in the reef ecosystem through fertilization. We conclude that dust may influence air‐sea CO2 exchange at other coral reefs regularly impacted by dust deposition, such as in the Caribbean and northwest Australia. Key Points: Results from the first direct measurements of air‐sea CO2 exchange with the atmosphere over desert fringing coral reefs are presentedFringing coral reefs in the Gulf of Eilat were found to be a net sink of atmospheric CO2 during the summerFertilization of the low‐nutrient, low‐chlorophyll sea by dust was identified as a possible major influence on air‐sea CO2 exchange [ABSTRACT FROM AUTHOR]

Coral transcriptomic data largely rely on short-read sequencing, which severely limits the understanding of coral molecular mechanisms and leaves many important biological questions unresolved. Here, we sequence the full-length transcriptomes of four common and frequently dominant reef-building corals using the PacBio Sequel II platform. We obtain information on reported gene functions, structures, and expression profiles. Among them, a comparative analysis of biomineralization-related genes provides insights into the molecular basis of coral skeletal density. The gene expression profiles of the symbiont Symbiodiniaceae are also isolated and annotated from the holobiont sequence data. Finally, a phylogenetic analysis of key circadian clock genes among 40 evolutionarily representative species indicates that there are four key members in early metazoans, including cry genes; Clock or Npas2; cyc or Arntl; and tim, while per, as the fifth member, occurs in Bilateria. In summary, this work provides a foundation for further work on the manipulation of skeleton production or symbiosis to promote the survival of these important organisms. [ABSTRACT FROM AUTHOR]

Widespread mapping of coral thermal resilience is essential for developing effective management strategies and requires replicable and rapid multi-location assays of heat resistance and recovery. One- or two-day short-term heat stress experiments have been previously employed to assess heat resistance, followed by single assays of bleaching condition. We tested the reliability of short-term heat stress resistance, and linked resistance and recovery assays, by monitoring the phenotypic response of fragments from 101 Acropora hyacinthus colonies located in Palau (Micronesia) to short-term heat stress. Following short-term heat stress, bleaching and mortality were recorded after 16 hours, daily for seven days, and after one and two months of recovery. To follow corals over time, we utilized a qualitative, non-destructive visual bleaching score metric that correlated with standard symbiont retention assays. The bleaching state of coral fragments 16 hours post-heat stress was highly indicative of their state over the next 7 days, suggesting that symbiont population sizes within corals may quickly stabilize post-heat stress. Bleaching 16 hours post-heat stress predicted likelihood of mortality over the subsequent 3–5 days, after which there was little additional mortality. Together, bleaching and mortality suggested that rapid assays of the phenotypic response following short-term heat stress were good metrics of the total heat treatment effect. Additionally, our data confirm geographic patterns of intraspecific variation in Palau and show that bleaching severity among colonies was highly correlated with mortality over the first week post-stress. We found high survival (98%) and visible recovery (100%) two months after heat stress among coral fragments that survived the first week post-stress. These findings help simplify rapid, widespread surveys of heat sensitivity in Acropora hyacinthus by showing that standardized short-term experiments can be confidently assayed after 16 hours, and that bleaching sensitivity may be linked to subsequent survival using experimental assessments. [ABSTRACT FROM AUTHOR]

The symbiotic relationship between dinoflagellate algae in the family Symbiodiniaceae and scleractinian corals forms the base of the tropical reef ecosystem. In scleractinian corals, recruits acquire symbionts either "vertically" from the maternal colony or initially lack symbionts and acquire them "horizontally" from the environment. Regardless of the mode of acquisition, coral species and individual colonies harbor only a subset of the highly diverse complex of species/taxa within the Symbiodiniaceae. This suggests a genetic basis for specificity, but local environmental conditions and/or symbiont availability may also play a role in determining which symbionts within the Symbiodiniaceae are initially taken up by the host. To address the relative importance of genetic and environmental drivers of symbiont uptake/establishment, we examined the acquisition of these dinoflagellate symbionts in one to three‐month‐old recruits of Orbicella faveolata to compare symbiont types present in recruits to those of parental populations versus co‐occurring adults in their destination reef. Variation in chloroplast 23S ribosomal DNA and in three polymorphic microsatellite loci was examined. We found that, in general, symbiont communities within adult colonies differed between reefs, suggesting that endemism is common among symbiont populations of O. faveolata on a local scale. Among recruits, initial symbiont acquisition was selective. O. faveolata recruits only acquired a subset of locally available symbionts, and these generally did not reflect symbiont populations in adults at either the parental or the outplant reef. Instead, symbiont communities within new recruits at a given outplant site and region tended to be similar to each other, regardless of parental source population. These results suggest temporal variation in the local symbiont source pool, although other possible drivers behind the distinct difference between symbionts within O. faveolata adults and new generations of recruits may include different ontogenetic requirements and/or reduced host selectivity in early ontogeny. [ABSTRACT FROM AUTHOR]

Global change driven by anthropogenic carbon emissions is altering ecosystems at unprecedented rates, especially coral reefs, whose symbiosis with algal symbionts is particularly vulnerable to increasing ocean temperatures and altered carbonate chemistry. Here, we assess the physiological responses of three Caribbean coral (animal host + algal symbiont) species from an inshore and offshore reef environment after exposure to simulated ocean warming (28, 31°C), acidification (300–3290 μatm), and the combination of stressors for 93 days. We used multidimensional analyses to assess how a variety of coral physiological parameters respond to ocean acidification and warming. Our results demonstrate reductions in coral health in Siderastrea siderea and Porites astreoides in response to projected ocean acidification, while future warming elicited severe declines in Pseudodiploria strigosa. Offshore S. siderea fragments exhibited higher physiological plasticity than inshore counterparts, suggesting that this offshore population was more susceptible to changing conditions. There were no plasticity differences in P. strigosa and P. astreoides between natal reef environments, however, temperature evoked stronger responses in both species. Interestingly, while each species exhibited unique physiological responses to ocean acidification and warming, when data from all three species are modelled together, convergent stress responses to these conditions are observed, highlighting the overall sensitivities of tropical corals to these stressors. Our results demonstrate that while ocean warming is a severe acute stressor that will have dire consequences for coral reefs globally, chronic exposure to acidification may also impact coral physiology to a greater extent in some species than previously assumed. Further, our study identifies S. siderea and P. astreoides as potential 'winners' on future Caribbean coral reefs due to their resilience under projected global change stressors, while P. strigosa will likely be a 'loser' due to their sensitivity to thermal stress events. Together, these species-specific responses to global change we observe will likely manifest in altered Caribbean reef assemblages in the future. [ABSTRACT FROM AUTHOR]