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Corals have complex symbiotic associations that can be influenced by the environment. We compare symbiotic dinoflagellate (family: Symbiodiniaceae) associations and the microbiome of five scleractinian coral species from three different reef habitats in Palau, Micronesia. Although pH and temperature corresponded with specific host‐Symbiodiniaceae associations common to the nearshore and offshore habitats, bacterial community dissimilarity analyses indicated minimal influence of these factors on microbial community membership for the corals Coelastrea aspera, Psammocora digitata, and Pachyseris rugosa. However, coral colonies sampled close to human development exhibited greater differences in microbial community diversity compared to the nearshore habitat for the coral species Coelastrea aspera, Montipora foliosa, and Pocillopora acuta, and the offshore habitat for Coelastrea aspera, while also showing less consistency in Symbiodiniaceae associations. These findings indicate the influence that habitat location has on the bacterial and Symbiodiniaceae communities comprising the coral holobiont and provide important considerations for the conservation of coral reef communities, especially for island nations with increasing human populations and development. [ABSTRACT FROM AUTHOR]

The ecological and evolutionary consequences of partner fidelity and flexibility among coral–dinoflagellate mutualisms are widely debated. Resident symbionts can modulate the resilience of their hosts to environmental stressors, which explains, in part, why host–symbiont combinations differ over broad geographic ranges and across physical–environmental gradients in light and temperature. Therefore, flexibility in these mutualisms may influence the longevity of coral populations and communities subjected to ocean warming. However, despite decades of research, basic knowledge about these mutualisms remains incomplete, hindering the development of predictive ecological theory. In particular, few studies have investigated the long-term composition of symbiont populations within individual colonies. To further examine the extent to which coral colonies have stable relationships with specific symbionts over multiple years, diverse coral taxa (Scleractinia) from a West Indo-Pacific fore reef (Palau) were tagged and sampled at various intervals—ranging from six months to several years—over nine years' time. Symbiont identity was examined using multiple genetic markers that resolved symbiont diversity to species and individual genotypes (i.e., clonal strains). Members of the genus Cladocopium (formerly Symbiodinium Clade C) were prevalent across the host community. Generally, corals with open modes of symbiont acquisition harbored a host–generalist symbiont, while corals with vertical symbiont transmission were associated with co-evolved host-specific symbionts. Consistent with previous colony monitoring studies, symbiont populations in a majority of colonies were dominated by one species and one strain (based on multilocus genotyping) over multiple years. Thus, the distribution of symbiont diversity at the genus, species and clone level, comprising specific and stable partner combinations, scale predictably to reef habitat, host taxon, and individual colony. Recognizing these fundamental ecological patterns establishes a more comprehensive understanding of the population and community structure of these mutualisms. [ABSTRACT FROM AUTHOR]

Corals with high levels of total lipids are known to have increased resilience potential to bleaching, and lipid class management may shed further light on why some species are more resilient to, or are able to acclimatize to, annual bleaching stress. Here, we measured the lipid class composition of three species of Caribbean corals (Porites astreoides, Porites divaricata, and Orbicella faveolata) collected in July 2009 near Puerto Morelos, Mexico (20° 50' N, 86° 52' W) that were experimentally bleached 2 years in a row. Our results show that single bleaching can significantly alter lipid class composition in all species, while repeated bleaching can result in stable (i.e., acclimatized) or even more altered (i.e., not acclimatized) lipid class composition depending on the species. Specifically, P. divaricata and O. faveolata both had altered lipid class composition with losses in storage lipids following single bleaching, but maintained lipid class composition following repeated bleaching stress. However, both single and repeated bleaching altered the lipid class composition in P. astreoides, with changes persisting for the 6 weeks after repeated bleaching stress. This study provides evidence that lipid class management is part of the suite of variables associated with coral resilience, that P. divaricata and O. faveolata acclimatize their lipid class management in response to repeated bleaching stress, but that P. astreoides does not. Corals like P. divaricata and O. faveolata may, therefore, be more suitable for coral restoration efforts since they are more likely to persist under chronic repeat bleaching scenarios predicted for later this century., Author(s): Sarah L. Solomon [sup.1], Andréa G. Grottoli [sup.1], Mark E. Warner [sup.2], Stephen Levas [sup.1] [sup.3], Verena Schoepf [sup.1] [sup.4], Agustí Muñoz-Garcia [sup.5] Author Affiliations: (1) 0000 0001 2285 [...]

Symbiotic mutualisms are essential to ecosystems and numerous species across the tree of life. For reef-building corals, the benefits of their association with endosymbiotic dinoflagellates differ within and across taxa, and nutrient exchange between these partners is influenced by environmental conditions. Furthermore, it is widely assumed that corals associated with symbionts in the genus Durusdinium tolerate high thermal stress at the expense of lower nutrient exchange to support coral growth. We traced both inorganic carbon (H13CO3–) and nitrate (15NO3–) uptake by divergent symbiont species and quantified nutrient transfer to the host coral under normal temperatures as well as in colonies exposed to high thermal stress. Colonies representative of diverse coral taxa associated with Durusdinium trenchii or Cladocopium spp. exhibited similar nutrient exchange under ambient conditions. By contrast, heat-exposed colonies with D. trenchii experienced less physiological stress than conspecifics with Cladocopium spp. while high carbon assimilation and nutrient transfer to the host was maintained. This discovery differs from the prevailing notion that these mutualisms inevitably suffer trade-offs in physiological performance. These findings emphasize that many host–symbiont combinations adapted to high-temperature equatorial environments are high-functioning mutualisms; and why their increased prevalence is likely to be important to the future productivity and stability of coral reef ecosystems. [ABSTRACT FROM AUTHOR]

The existence of widespread species with the capacity to endure diverse, or variable, environments are of importance to ecological and genetic research, and conservation. Such "ecological generalists" are more likely to have key adaptations that allow them to better tolerate the physiological challenges of rapid climate change. Reef‐building corals are dependent on endosymbiotic dinoflagellates (Family: Symbiodiniaceae) for their survival and growth. While these symbionts are biologically diverse, certain genetic types appear to have broad geographic distributions and are mutualistic with various host species from multiple genera and families in the order Scleractinia that must acquire their symbionts through horizontal transmission. Despite the considerable ecological importance of putative host‐generalist symbionts, they lack formal species descriptions. In this study, we used molecular, ecological, and morphological evidence to verify the existence of five new host‐generalist species in the symbiodiniacean genus Cladocopium. Their geographic distribution and prevalence among host communities corresponds to prevailing environmental conditions at both regional and local scales. The influence that each species has on host physiology may partially explain regional differences in thermal sensitivities among coral communities. The potential increased prevalence of a generalist species that endures environmental instability is a consequential ecological response to warming oceans. Large‐scale shifts in symbiont dominance could ensure reef coral persistence and productivity in the near term. Ultimately, these formal designations should advance scientific communication and generate informed research questions on the physiology and ecology of coral‐dinoflagellate mutualisms. [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]

The global impacts of climate change are evident in every marine ecosystem. On coral reefs, mass coral bleaching and mortality have emerged as ubiquitous responses to ocean warming, yet one of the greatest challenges of this epiphenomenon is linking information across scientific disciplines and spatial and temporal scales. Here we review some of the seminal and recent coral-bleaching discoveries from an ecological, physiological, and molecular perspective. We also evaluate which data and processes can improve predictive models and provide a conceptual framework that integrates measurements across biological scales. Taking an integrative approach across biological and spatial scales, using for example hierarchical models to estimate major coral-reef processes, will not only rapidly advance coral-reef science but will also provide necessary information to guide decision-making and conservation efforts. To conserve reefs, we encourage implementing mesoscale sanctuaries (thousands of km2) that transcend national boundaries. Such networks of protected reefs will provide reef connectivity, through larval dispersal that transverse thermal environments, and genotypic repositories that may become essential units of selection for environmentally diverse locations. Together, multinational networks may be the best chance corals have to persist through climate change, while humanity struggles to reduce emissions of greenhouse gases to net zero. [ABSTRACT FROM AUTHOR]

Active chlorophyll a fluorometry is a well‐established tool for noninvasively diagnosing coral functional state, but has not yet been developed as a rapid phenotyping (functional screening) platform as for agriculture and forestry. Here, we present a proof‐of‐concept using Light‐Induced Fluorescence Transient‐Fast Repetition Rate fluorometry (LIFT‐FRRf) to identify coral photobiological‐based phenotypes in the context of rapidly scaling coral propagation practices on the northern Great Barrier Reef. For example, resolving light niche plasticity to inform transplantation, and identifying functionally diverse colonies to maximize stock selection. We first used optically diverse laboratory‐reared corals and coral endosymbiont (Symbiodiniaceae) isolates to develop a phenotyping approach integrating FRRf instantaneous kinetic parameters (light harvesting, electron turnover rates) and light‐dependent parameters (dynamic "quenching" terms, saturating light intensity [EK]). Subsequent field‐based LIFT‐FRRf phenotyping of coral from a selective (2‐4 m depth) reef habitat revealed that widely topographically dispersed plating Acropora taxa exhibited broad light niche plasticity (EK variance) underpinned by multiple phenotypes that were predominantly differentiated by minimum electron turnover capacity; fluorometer configurations that cannot resolve kinetic parameters will thus likely have more limited capacity to resolve phenotypes. As such, plating Acropora have broad propagation potential in terms of multiple functional variants for stock and across diverse light environments (growth, transplantation). In contrast, coral taxa (Pocillopora verrucosa, Echinopora lamellosa) with relatively restricted topographic dispersion exhibited less light niche plasticity and only single phenotypes, thereby imposing more constraints for propagation. We discuss the core technical, operational, and conceptual steps required to develop more sophisticated coral phenotyping platforms. [ABSTRACT FROM AUTHOR]

Reef‐building corals in the genus Porites are one of the most important constituents of Indo‐Pacific reefs. Many species within this genus tolerate abnormally warm water and exhibit high specificity for particular kinds of endosymbiotic dinoflagellates that cope with thermal stress better than those living in other corals. Still, during extreme ocean heating, some Porites exhibit differences in their stress tolerance. While corals have different physiological qualities, it remains unknown whether the stability and performance of these mutualisms is influenced by the physiology and genetic relatedness of their symbionts. We investigated two ubiquitous Pacific reef corals, Porites rus and Porites cylindrica, from warmer inshore and cooler offshore reef systems in Palau. While these corals harbored a similar kind of symbiont in the genus Cladocopium (within the ITS2 C15 subclade), rapidly evolving genetic markers revealed evolutionarily diverged lineages corresponding to each Porites species living in each reef habitat. Furthermore, these closely related Cladocopium lineages were differentiated by their densities in host tissues, cell volume, chlorophyll concentration, gross photosynthesis, and photoprotective pathways. When assessed using several physiological proxies, these previously undifferentiated symbionts contrasted in their tolerance to thermal stress. Symbionts within P. cylindrica were relatively unaffected by exposure to 32℃ for 14 days, whereas P. rus colonies lost substantial numbers of photochemically compromised symbionts. Heating reduced the ability of the offshore symbiont associated with P. rus to translocate carbon to the coral. By contrast, high temperatures enhanced symbiont carbon assimilation and delivery to the coral skeleton of inshore P. cylindrica. This study indicates that large physiological differences exist even among closely related symbionts, with significant implications for thermal susceptibility among reef‐building Porites. [ABSTRACT FROM AUTHOR]

Under predicted future ocean conditions, reefs exposed to elevated nutrients will simultaneously experience ocean acidification and elevated temperature. We evaluated if moderate nutrients mitigate, minimize, or exacerbate negative effects of predicted future ocean conditions on coral physiology. For 30 days, Acropora millepora and Turbinaria reniformis were exposed to a fully factorial experiment of eight treatments including two seawater temperatures (26.4 °C and 29.8 °C), pCO2 levels (401 μatm pCO2 and 760 μatm pCO2), and nutrient concentrations (ambient: 0.40 μmol L−1 NO3− and 0.22 μmol L−1 PO43−, and moderate: 3.56 μmol L−1 NO3− and 0.31 μmol L−1 PO43−). Added nitrate was taken up by the algal endosymbionts and transferred to the coral hosts in both species, though to a much higher degree in A. millepora. When exposed to elevated temperature, elevated pCO2, or both, effects observed for chlorophyll a, calcification, biomass, and energy reserves were not compounded by the moderate nutrient concentrations in either species. Moderate nutrients enabled A. millepora to continue to meet daily metabolic demand via photosynthesis under predicted future ocean conditions and T. reniformis to greatly exceed daily metabolic demand via photosynthesis and heterotrophy. Our results suggest that balanced moderate nutrients are not detrimental to corals under predicted future ocean conditions and may even provide some benefits. [ABSTRACT FROM AUTHOR]

Dinoflagellates within the family Symbiodiniaceae are widespread and fuel metabolism of reef‐forming corals through photosynthesis. Adaptation in capacity to harvest and utilize light, and "safely" process photosynthetically generated energy is a key factor regulating their broad ecological success. However, whether such adaptive capacity similarly extends to how Symbiodiniaceae species and genotypes assimilate inorganic carbon (Ci) remains unexplored. We build on recent approaches exploring functional diversity of fitness traits to identify whether Ci uptake and incorporation could be reconciled with evolutionary adaptation among Symbiodiniaceae. We examined phylogenetically diverse Symbiodiniaceae cultures (23 isolates, 6 genera) to track how carbon was invested into cellular uptake, excretion, and growth (cell size, division, storage). Gross carbon uptake rates (GPC) over 1 h varied among isolates grown at 26°C (0.63–3.08 pg C [cell h]−1) with no evident pattern with algal phylogeny. Intriguingly, net carbon uptake rates (24 h) were often higher (1.01–5.54 pg C [cell h]−1) than corresponding values of GPC—we discuss how such GPC measurements may reflect highly conserved biological characteristics for cultured cells linked to high metabolic dependency on photorespiration and heterotrophy. Three isolates from different genera (Cladocopium goreaui, Durusdinium trenchii, and Effrenium voratum) were additionally grown at 20°C and 30°C. Here, Ci uptake consistently decreased with temperature‐driven declines in growth rate, suggesting environmental regulation outweighs phylogenetic organization of carbon assimilation capacity among Symbiodiniaceae. Together, these data demonstrate environmental regulation and ecological success among Symbiodiniaceae likely rests on plasticity of upstream photosynthetic processes (light harvesting, energy quenching, etc.) to overcome evolutionary‐conserved limitations in Ci functioning. [ABSTRACT FROM AUTHOR]

Corals with high levels of total lipids are known to have increased resilience potential to bleaching, and lipid class management may shed further light on why some species are more resilient to, or are able to acclimatize to, annual bleaching stress. Here, we measured the lipid class composition of three species of Caribbean corals (Porites astreoides, Porites divaricata, and Orbicella faveolata) collected in July 2009 near Puerto Morelos, Mexico (20° 50′ N, 86° 52′ W) that were experimentally bleached 2 years in a row. Our results show that single bleaching can significantly alter lipid class composition in all species, while repeated bleaching can result in stable (i.e., acclimatized) or even more altered (i.e., not acclimatized) lipid class composition depending on the species. Specifically, P. divaricata and O. faveolata both had altered lipid class composition with losses in storage lipids following single bleaching, but maintained lipid class composition following repeated bleaching stress. However, both single and repeated bleaching altered the lipid class composition in P. astreoides, with changes persisting for the 6 weeks after repeated bleaching stress. This study provides evidence that lipid class management is part of the suite of variables associated with coral resilience, that P. divaricata and O. faveolata acclimatize their lipid class management in response to repeated bleaching stress, but that P. astreoides does not. Corals like P. divaricata and O. faveolata may, therefore, be more suitable for coral restoration efforts since they are more likely to persist under chronic repeat bleaching scenarios predicted for later this century. [ABSTRACT FROM AUTHOR]

Rising seawater temperature and ocean acidification threaten the survival of coral reefs. The relationship between coral physiology and its microbiome may reveal why some corals are more resilient to these global change conditions. Here, we conducted the first experiment to simultaneously investigate changes in the coral microbiome and coral physiology in response to the dual stress of elevated seawater temperature and ocean acidification expected by the end of this century. Two species of corals, Acropora millepora containing the thermally sensitive endosymbiont C21a and Turbinaria reniformis containing the thermally tolerant endosymbiont Symbiodinium trenchi, were exposed to control (26.5°C and pCO2 of 364 μatm) and treatment (29.0°C and pCO2 of 750 μatm) conditions for 24 days, after which we measured the microbial community composition. These microbial findings were interpreted within the context of previously published physiological measurements from the exact same corals in this study (calcification, organic carbon flux, ratio of photosynthesis to respiration, photosystem II maximal efficiency, total lipids, soluble animal protein, soluble animal carbohydrates, soluble algal protein, soluble algal carbohydrate, biomass, endosymbiotic algal density, and chlorophyll a). Overall, dually stressed A. millepora had reduced microbial diversity, experienced large changes in microbial community composition, and experienced dramatic physiological declines in calcification, photosystem II maximal efficiency, and algal carbohydrates. In contrast, the dually stressed coral T. reniformis experienced a stable and more diverse microbiome community with minimal physiological decline, coupled with very high total energy reserves and particulate organic carbon release rates. Thus, the microbiome changed and microbial diversity decreased in the physiologically sensitive coral with the thermally sensitive endosymbiotic algae but not in the physiologically tolerant coral with the thermally tolerant endosymbiont. Our results confirm recent findings that temperature-stress tolerant corals have a more stable microbiome, and demonstrate for the first time that this is also the case under the dual stresses of ocean warming and acidification. We propose that coral with a stable microbiome are also more physiologically resilient and thus more likely to persist in the future, and shape the coral species diversity of future reef ecosystems. [ABSTRACT FROM AUTHOR]

Coral reefs are under assault from stressors including global warming, ocean acidification, and urbanization. Knowing how these factors impact the future fate of reefs requires delineating stress responses across ecological, organismal and cellular scales. Recent advances in coral reef biology have integrated molecular processes with ecological fitness and have identified putative suites of temperature acclimation genes in a Scleractinian coral Acropora hyacinthus. We wondered what unique characteristics of these genes determined their coordinate expression in response to temperature acclimation, and whether or not other corals and cnidarians would likewise possess these features. Here, we focus on cytosine methylation as an epigenetic DNA modification that is responsive to environmental stressors. We identify common conserved patterns of cytosine-guanosine dinucleotide (CpG) motif frequencies in upstream promoter domains of different functional gene groups in two cnidarian genomes: a coral (Acropora digitifera) and an anemone (Nematostella vectensis). Our analyses show that CpG motif frequencies are prominent in the promoter domains of functional genes associated with environmental adaptation, particularly those identified in A. hyacinthus. Densities of CpG sites in upstream promoter domains near the transcriptional start site (TSS) are 1.38x higher than genomic background levels upstream of -2000 bp from the TSS. The increase in CpG usage suggests selection to allow for DNA methylation events to occur more frequently within 1 kb of the TSS. In addition, observed shifts in CpG densities among functional groups of genes suggests a potential role for epigenetic DNA methylation within promoter domains to impact functional gene expression responses in A. digitifera and N. vectensis. Identifying promoter epigenetic sequence motifs among genes within specific functional groups establishes an approach to describe integrated cellular responses to environmental stress in reef corals and potential roles of epigenetics on survival and fitness in the face of global climate change. [ABSTRACT FROM AUTHOR]

Coral skeletal boron isotopes have been established as a proxy for seawater pH, yet it remains unclear if and how this proxy is affected by seawater temperature. Specifically, it has never been directly tested whether coral bleaching caused by high water temperatures influences coral boron isotopes. Here we report the results from a controlled bleaching experiment conducted on the Caribbean corals Porites divaricata, Porites astreoides, and Orbicella faveolata. Stable boron (δ11B), carbon (δ13C), oxygen (δ18O) isotopes, Sr/Ca, Mg/Ca, U/Ca, and Ba/Ca ratios, as well as chlorophyll a concentrations and calcification rates were measured on coral skeletal material corresponding to the period during and immediately after the elevated temperature treatment and again after 6 weeks of recovery on the reef. We show that under these conditions, coral bleaching did not affect the boron isotopic signature in any coral species tested, despite significant changes in coral physiology. This contradicts published findings from coral cores, where significant decreases in boron isotopes were interpreted as corresponding to times of known mass bleaching events. In contrast, δ13C and δ18O exhibited major enrichment corresponding to decreases in calcification rates associated with bleaching. Sr/Ca of bleached corals did not consistently record the 1.2°C difference in seawater temperature during the bleaching treatment, or alternatively show a consistent increase due to impaired photosynthesis and calcification. Mg/Ca, U/Ca, and Ba/Ca were affected by coral bleaching in some of the coral species, but the observed patterns could not be satisfactorily explained by temperature dependence or changes in coral physiology. This demonstrates that coral boron isotopes do not record short-term bleaching events, and therefore cannot be used as a proxy for past bleaching events. The robustness of coral boron isotopes to changes in coral physiology, however, suggests that reconstruction of seawater pH using boron isotopes should be uncompromised by short-term bleaching events. [ABSTRACT FROM AUTHOR]

Mutualistic symbioses between scleractinian corals and endosymbiotic dinoflagellates (Symbiodinium spp.) are the foundation of coral reef ecosystems. For many coral-algal symbioses, prolonged episodes of thermal stress damage the symbiont's photosynthetic capability, resulting in its expulsion from the host. Despite the link between photosynthetic competency and symbiont expulsion, little is known about the effect of thermal stress on the expression of photosystem genes in Symbiodinium. This study used real-time PCR to monitor the transcript abundance of two important photosynthetic reaction center genes, psbA (encoding the D1 protein of photosystem II) and psaA (encoding the P700 protein of photosystem I), in four cultured isolates (representing ITS2-types A13, A20, B1, and F2) and two in hospite Symbiodinium spp. within the coral Pocillopora spp. (ITS2-types C1b-c and D1). Both cultured and in hospite Symbiodinium samples were exposed to elevated temperatures (32°C) over a 7-day period and examined for changes in photochemistry and transcript abundance. Symbiodinium A13 and C1b-c (both thermally sensitive) demonstrated significant declines in both psbA and psaA during the thermal stress treatment, whereas the transcript levels of the other Symbiodinium types remained stable. The downregulation of both core photosystem genes could be the result of several different physiological mechanisms, but may ultimately limit repair rates of photosynthetic proteins, rendering some Symbiodinium spp. especially susceptible to thermal stress. [ABSTRACT FROM AUTHOR]

Increased seawater pCO2, and in turn 'ocean acidification' (OA), is predicted to profoundly impact marine ecosystem diversity and function this century. Much research has already focussed on calcifying reef-forming corals (Class: Anthozoa) that appear particularly susceptible to OA via reduced net calcification. However, here we show that OA-like conditions can simultaneously enhance the ecological success of non-calcifying anthozoans, which not only play key ecological and biogeochemical roles in present day benthic ecosystems but also represent a model organism should calcifying anthozoans exist as less calcified (soft-bodied) forms in future oceans. Increased growth (abundance and size) of the sea anemone ( Anemonia viridis) population was observed along a natural CO2 gradient at Vulcano, Italy. Both gross photosynthesis ( PG) and respiration (R) increased with pCO2 indicating that the increased growth was, at least in part, fuelled by bottom up (CO2 stimulation) of metabolism. The increase of PG outweighed that of R and the genetic identity of the symbiotic microalgae ( Symbiodinium spp.) remained unchanged (type A19) suggesting proximity to the vent site relieved CO2 limitation of the anemones' symbiotic microalgal population. Our observations of enhanced productivity with pCO2, which are consistent with previous reports for some calcifying corals, convey an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater pCO2. Understanding how CO2-enhanced productivity of non- (and less-) calcifying anthozoans applies more widely to tropical ecosystems is a priority where such organisms can dominate benthic ecosystems, in particular following localized anthropogenic stress. [ABSTRACT FROM AUTHOR]

In the original article, the light cycle was indicated as 12:12 h light:dark. [ABSTRACT FROM AUTHOR]

Mass coral bleaching events are increasing in frequency and intensity and are predicted to occur annually in the coming decades. However, it remains poorly understood how quickly Caribbean corals can recover from bleaching. To explore the responses to heat stress and subsequent recovery in Caribbean corals, three species ( Porites divaricata , Porites astreoides , and Orbicella faveolata ) were experimentally bleached in outdoor flow-through tanks for 15 days then allowed to recover on the reef for 1.5 and 11 months. At each interval on the reef, endosymbiont concentrations, energy reserves (i.e., total soluble lipid, soluble animal carbohydrate, soluble animal protein), calcification, and stable carbon and nitrogen isotope values of the animal host (δ 13 C h , δ 15 N h ) and endosymbiotic algal fractions (δ 13 C e , δ 15 N e ) were measured in treatment and control fragments of each species. Despite variations in bleaching recovery strategies among the coral species, all corals recovered within one year. Specifically, bleached P. divaricata catabolized lipids and decreased calcification in response to lower endosymbiont concentrations. In contrast, both P. astreoides and O. faveolata maintained energy reserves despite lower endosymbiont concentrations, yet both decreased calcification rates after bleaching. Overall, these findings indicate that these corals are capable of surviving and recovering from a mild bleaching event within one year. Though these finding indicate that P. astreoides and O. faveolata may be resilient through single isolated bleaching events under annual bleaching, many Caribbean coral reefs may still experience a decline over the coming decades. [ABSTRACT FROM AUTHOR]

Anthropogenic ocean warming is one of the biggest threats to marine organisms worldwide. However, it remains unclear how the duration and intensity of thermal anomalies affect organismal stress responses and thermal thresholds. We used detailed tracking of coral endosymbiont and host physiology and dose-response analyses to compare the effects of multiple heating rates, intensities, and exposure durations on two reef-building corals, Acropora hemprichii and Porites lobata , from adjacent sides of a reef (protected vs. exposed) in the Central Red Sea known to differ in high-frequency (< 24 h) temperature variability. Corals were exposed to acute heat exposures (18 h) with four target temperatures (32 °C, 35 °C, 36.5 °C, and 38 °C), versus prolonged heat exposures lasting 7–15 days where temperatures were raised 0.5 and 1.5 °C day−1 to four target temperatures (32 °C, 33.5 °C, 35 °C, and 36.5 °C). In the prolonged experiment, dose-response curves assessing algal endosymbiont F v /F m revealed little initial effect of temperature, before an exponential decline above 34 °C for both species. Temperature at time of measurement and degree heating hours above 34 °C (DHH 34) were the variables most strongly associated with declines in F v /F m. The F v /F m thermal thresholds for P. lobata from the high-variability protected site were higher than the exposed site in the faster heating, prolonged heat stress experiment despite minimal differences in endosymbiont density, chlorophyll- a , and host protein between sites. Together, our dose-response analysis revealed complex effects of DHH 34 , heating rate, and species-specific differences in the influence of local thermal histories shaping thermotolerance limits for these corals. • Dose-response analyses were used to compare the effects of multiple heating rates, intensities, and exposure times on corals • Two coral species from reefs contrasting in thermal histories were subjected to acute (18 h) and prolonged (7–15 d) heating • Coral symbionts showed strong declines in F v /F m when exposed to temperatures above 34 °C (degree heating hours above 34 °C) • Porites lobata from the high variability reef had higher F v /F m thermal thresholds than those from the low variability reef • Degree heating hours > 34°C, heating rate, and species-specific influences of thermal history affected coral thermal limits [ABSTRACT FROM AUTHOR]

Abstract: In 2007 and 2008, multiple sites were identified in the Wakatobi Marine National Park, South East Sulawesi, Indonesia, which each represented a point along a gradient of light quality, temperature and turbidity. This gradient included ‘optimal’, intermediate and marginal sites, where conditions were close to the survival threshold limit for corals. Coral communities changed across this gradient from diverse, mixed growth form assemblages to specialised, massive growth form dominated communities. The massive coral Goniastrea aspera was the only species identified at the most marginal and optimal sites. Branching species Acropora formosa and Porites cylindrica were only identified at optimal sites. The in hospite Symbiodinium community also changed across the environmental gradient from members of the Symbiodinium clade C on optimal reefs (in branching and massive species) to clade D on marginal reefs (in massive species). Substantial variability in respiration and photosynthesis was observed in massive coral species under different environmental conditions, which suggests that all corals cannot be considered equal across environments. Studying present-day marginal environments is crucial to further understanding of future reef bio-diversity, functioning and accretion, and from work presented here, it is likely that as future climate change extends marginal reef range, branching coral diversity may decrease relative to massive, more resilient corals. [ABSTRACT FROM AUTHOR]