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Increasing ocean temperatures have widespread consequences for coral reefs, one of which is coral bleaching. We analyzed a global network of associations between coral species and Symbiodiniaceae for resistance to temperature stress and robustness to perturbations. Null networks were created by changing either the physiological parameters of the nodes or the structures of the networks. We developed a bleaching model in which each link, association, is given a weight based on temperature thresholds for specific host–symbiont pairs and links are removed as temperature increases. Resistance to temperature stress was determined from the response of the networks to the bleaching model. Ecological robustness, defined by how much perturbation is needed to decrease the number of nodes by 50%, was determined for multiple removal models that considered traits of the hosts, symbionts, and their associations. Network resistance to bleaching and robustness to perturbations differed from the null networks and varied across spatial scales, supporting that thermal tolerances, local association patterns, and environment play an important role in network persistence. Networks were more robust to attacks on associations than to attacks on species. Although the global network was fairly robust to random link removals, when links are removed according to the bleaching model, robustness decreases by about 20%. Specific environmental attacks, in the form of increasing temperatures, destabilize the global network of coral species and Symbiodiniaceae. On a global scale, the network was more robust to removals of links with susceptible Symbiodiniaceae than it was to removals of links with susceptible hosts. Thus, the symbionts convey more stability to the symbiosis than the hosts when the system is under an environmental attack. However, our results also provide evidence that the environment of the networks affects robustness to link perturbations. Our work shows that ecological resistance and robustness can be assessed through network analysis that considers specific biological traits and functional weaknesses. The global network of associations between corals and Symbiodiniaceae and its distribution of thermal tolerances are non‐random, and the evolution of this architecture has led to higher sensitivity to environmental perturbations. [ABSTRACT FROM AUTHOR]

The knowledges of trophic status (i.e., autotrophy/heterotrophy) of corals are helpful for understanding the mechanisms driving their environmental stress tolerance and bleaching resilience. We conducted this study to elucidate the differences in trophic status among corals of different genera and then explore the implication of trophic status for their different environmental stress tolerance. In this study, 117 coral samples including five genera (i.e., relatively stress‐tolerant massive genera Porites, Favites, and Favia and relatively vulnerable plating genus Pavona and branching genus Acropora) were collected from Weizhou Island, northern South China Sea. The symbiotic zooxanthellae density, δ13C of host tissues (δ13Ch), and symbiotic zooxanthellae (δ13Cz) were measured. Besides, the difference in values between δ13Ch and δ13Cz (i.e., △h‐z 13C) was analyzed. Our results indicated that both zooxanthellae density and δ13Cz values of Porites, Favites, and Favia are higher than that of Pavona and Acropora and indicate that autotrophic photosynthesis intensity of symbiotic zooxanthellae of Porites, Favites, and Favia is higher than that of Pavona and Acropora. Besides, both δ13Ch and △h‐z 13C of Porites, Favites, and Favia are lower than that of Pavona and Acropora and indicate a higher contribution of heterotrophic predation to the coral host of Porites, Favites, and Favia. These comparisons suggest that trophic status of relatively stress‐tolerant Porites, Favites, and Favia is more plasticity than vulnerable Pavona and Acropora, which is conducive to maintain a positive energy budget. This is one of important factors leading to different environmental stress tolerance and bleaching resilience among corals of different genera. Key Points: Autotrophic photosynthesis and heterotrophic predation of massive corals are higher than that of plating and branching coralsTrophic status of relatively stress‐tolerant massive corals is more plasticity than that of vulnerable plating and branching coralsDifferent trophic status is one of important factors leading to different environmental stress tolerance and bleaching resilience [ABSTRACT FROM AUTHOR]

Summary: The intimate relationship between scleractinian corals and their associated microorganisms is fundamental to healthy coral reef ecosystems. Coral‐associated microbes (Symbiodiniaceae and other protists, bacteria, archaea, fungi and viruses) support coral health and resilience through metabolite transfer, inter‐partner signalling, and genetic exchange. However, much of our understanding of the coral holobiont relationship has come from studies that have investigated either coral‐Symbiodiniaceae or coral‐bacteria interactions in isolation, while relatively little research has focused on other ecological and metabolic interactions potentially occurring within the coral multi‐partner symbiotic network. Recent evidences of intimate coupling between phytoplankton and bacteria have demonstrated that obligate resource exchange between partners fundamentally drives their ecological success. Here, we posit that similar associations with bacterial consortia regulate Symbiodiniaceae productivity and are in turn central to the health of corals. Indeed, we propose that this bacteria‐Symbiodiniaceae‐coral relationship underpins the coral holobiont's nutrition, stress tolerance and potentially influences the future survival of coral reef ecosystems under changing environmental conditions. Resolving Symbiodiniaceae‐bacteria associations is therefore a logical next step towards understanding the complex multi‐partner interactions occurring in the coral holobiont. [ABSTRACT FROM AUTHOR]

Coral reefs are declining globally as climate change and local water quality press environmental conditions beyond the physiological tolerances of holobionts—the collective of the host and its microbial symbionts. To assess the relationship between symbiont composition and holobiont stress tolerance, community diversity metrics were quantified for dinoflagellate endosymbionts (Family: Symbiodiniaceae) from eight Acropora millepora genets that thrived under or responded poorly to various stressors. These eight selected genets represent the upper and lower tails of the response distribution of 40 coral genets that were exposed to four stress treatments (and control conditions) in a 10‐day experiment. Specifically, four 'best performer' coral genets were analyzed at the end of the experiment because they survived high temperature, high pCO2, bacterial exposure, or combined stressors, whereas four 'worst performer' genets were characterized because they experienced substantial mortality under these stressors. At the end of the experiment, seven of eight coral genets mainly hosted Cladocopium symbionts, whereas the eighth genet was dominated by both Cladocopium and Durusdinium symbionts. Symbiodiniaceae alpha and beta diversity were higher in worst performing genets than in best performing genets. Symbiont communities in worst performers also differed more after stress exposure relative to their controls (based on normalized proportional differences in beta diversity), than did best performers. A generalized joint attribute model estimated the influence of host genet and treatment on Symbiodiniaceae community composition and identified strong associations among particular symbionts and host genet performance, as well as weaker associations with treatment. Although dominant symbiont physiology and function contribute to host performance, these findings emphasize the importance of symbiont community diversity and stochasticity as components of host performance. Our findings also suggest that symbiont community diversity metrics may function as indicators of resilience and have potential applications in diverse disciplines from climate change adaptation to agriculture and medicine. [ABSTRACT FROM AUTHOR]

Reef organisms influence microorganisms within the surrounding seawater, yet the spatial and temporal dynamics of seawater microbial communities located in proximity to corals are rarely investigated. To better understand reef seawater microbial community dynamics over time and space, we collected small-volume seawater samples during the day and night over a 72 hour period from three locations that differed in spatial distance from 5 Porites astreoides coral colonies on a shallow reef in St. John, U.S. Virgin Islands: near-coral (sampled 5 cm horizontally from each colony), reef-depth (sampled 2 m above each colony) and surface seawater (sampled 1 m from the seawater surface). At all time points and locations, we quantified abundances of microbial cells, sequenced small subunit rRNA genes of bacterial and archaeal communities, and measured inorganic nutrient concentrations. Prochlorococcus and Synechococcus cells were consistently elevated at night compared to day and these abundances changed over time, corresponding with temperature, nitrite, and silicate concentrations. During the day, bacterial and archaeal alpha diversity was significantly higher in reef-depth and near-coral seawater compared to the surface seawater, signifying that the reef influences the diversity of the seawater microorganisms. At night, alpha diversity decreased across all samples, suggesting that photosynthesis may favor a more taxonomically diverse community. While Prochlorococcus exhibited consistent temporal rhythmicity, additional taxa were enriched in reef seawater at night compared to day or in reef-depth compared to surface seawater based on their normalized sequence counts. There were some significant differences in nutrient concentrations and cell abundances between reef-depth and near-coral seawater but no clear trends. This study demonstrates that temporal variation supersedes small-scale spatial variation in proximity to corals in reef seawater microbial communities. As coral reefs continue to change in benthic composition worldwide, monitoring microbial composition in response to temporal changes and environmental fluctuations will help discern normal variability from longer lasting changes attributed to anthropogenic stressors and global climate change. [ABSTRACT FROM AUTHOR]

The density of dinoflagellate microalgae in the tissue of symbiotic corals is an important determinant for health and productivity of the coral animal. Yet, the specific mechanism for their regulation and the consequence for coral nutrition are insufficiently understood due to past methodological limitations to resolve the fine-scale metabolic consequences of fluctuating densities. Here, we characterized the physiological and nutritional consequences of symbiont density variations on the colony and tissue level in Stylophora pistillata from the Red Sea. Alterations in symbiont photophysiology maintained coral productivity and host nutrition across a broad range of symbiont densities. However, we demonstrate that density-dependent nutrient competition between individual symbiont cells, manifested as reduced nitrogen assimilation and cell biomass, probably creates the negative feedback mechanism for symbiont population growth that ultimately defines the steady-state density. Despite fundamental changes in symbiont nitrogen assimilation, we found no density-related metabolic optimum beyond which host nutrient assimilation or tissue biomass declined, indicating that host nutrient demand is sufficiently met across the typically observed range of symbiont densities under ambient conditions. [ABSTRACT FROM AUTHOR]

The article presents a study which examined the effects of river runoff and related changes in naturally extreme environment by analyzing Porites coral from the macrotidal nearshore Kimberley region in Australia. Topics include the use of elemental (Ba/Ca) and isotopic compositions, observational coastal sea surface salinity, and geochemical time series in the study.

Coral reefs are currently under threat as a consequence of local and global stressors, in particular, mass coral bleaching induced by climate warming. In conjunction with global cuts to carbon emissions, active restoration interventions are being investigated as an additional option to buy time while these stressors are mitigated. One intervention with the potential to improve recovery during or postbleaching involves the addition of probiotic treatments, that is the addition of microorganisms that provide benefits to the host. Fragments of the branching coral, Acropora millepora, were experimentally exposed to a bleaching event coupled with the inoculation of Symbiodiniaceae probiotics (Durusdinium trenchii and Cladocopium goreaui) to determine if these probiotic treatments could ameliorate bleaching related stress and mortality. Fragments inoculated with C. goreaui and exposed to 32°C for 6 days exhibited significantly less mortality (9.1 ± 5%) compared to corals exposed to 32°C without probiotics (66.7 ± 8%) or with D. trenchii (41.7 ± 9%). Fragments in the C. goreaui probiotic treatment also bleached less and exhibited the highest photosynthetic efficiency compared to fragments inoculated with the D. trenchii at 32°C. Internal transcribed spacer‐2 amplicon sequencing did not detect the inoculated D. trenchii and C. goreaui cells within A. millepora tissues at the end of the experiment, suggesting the corals did not reestablish symbiosis but instead used inoculated cells as a nutritional supplement, although other factors such as shuffling conditions may have had an effect. This study highlights that nutritional supplementation can possibly aid coral resilience to temperature stress, though a far more detailed understanding of the factors that influence host regulation during symbiosis establishment is required. [ABSTRACT FROM AUTHOR]

Reef‐building corals are at risk of extinction from ocean warming. While some corals can enhance their thermal limits by associating with dinoflagellate photosymbionts of superior stress tolerance, the extent to which symbiont communities will reorganize under increased warming pressure remains unclear. Here we show that corals in the hottest reefs in the world in the Persian Gulf maintain associations with the same symbionts across 1.5 years despite extreme seasonal warming and acute heat stress (≥35°C). Persian Gulf corals predominantly associated with Cladocopium (clade C) and most also hosted Symbiodinium (clade A) and/or Durusdinium (clade D). This is in contrast to the neighbouring and milder Oman Sea, where corals associated with Durusdinium and only a minority hosted background levels of Cladocopium. During acute heat stress, the higher prevalence of Symbiodinium and Durusdinium in bleached versus nonbleached Persian Gulf corals indicates that genotypes of these background genera did not confer bleaching resistance. Within symbiont genera, the majority of ITS2 rDNA type profiles were unique to their respective coral species, confirming the existence of host‐specific symbiont lineages. Notably, further differentiation among Persian Gulf sites demonstrates that symbiont populations are either isolated or specialized over tens to hundreds of kilometres. Thermal tolerance across coral species was associated with the prevalence of a single ITS2 intragenomic sequence variant (C3gulf), definitive of the Cladocopium thermophilum group. The abundance of C3gulf was highest in bleaching‐resistant corals and at warmer sites, potentially indicating a specific symbiont genotype (or set of genotypes) that may play a role in thermal tolerance that warrants further investigation. Together, our findings indicate that co‐evolution of host–Symbiodiniaceae partnerships favours fidelity rather than flexibility in extreme environments and under future warming. [ABSTRACT FROM AUTHOR]

Coral bleaching represents the most serious threat to contemporary coral reefs. In response, focus is being laid on understanding the cellular processes involved in the response of corals to the environmental stresses and the molecular mechanisms that determine the bleaching patterns. In the present study, a component of the cellular stress response such as the expression of the heat shock proteins (Hsps) was analyzed following the coral bleaching event which occurred in the central Red Sea (Saudi Arabia) in 2015. During this event, corals of different species, growth forms and sites showed variable bleaching susceptibility. In particular, we investigated the expression of Hsp70, Hsp60 and Hsp32 in both healthy and bleached colonies belonging to four different coral species (Goniopora lobata, Porites lobata, Seriatopora hystrix and Stylophora pistillata), in order to explore the intra- and inter-specific modulation of these biomarkers as well as the existence of spatial patterns of Hsp expression. In healthy colonies, the level of all the biomarkers was significantly different among the different species, although within each species it remained similar regardless of the distance from the shore. All the coral species showed a significant modulation of the Hsp expression in response to bleaching, whose typology and amplitude were species-specific. In all the species, Hsp70 and Hsp60 showed a coordinated dual expression, which, in response to bleaching resulted in an up-regulation in G. lobata and P. lobata and in a down-regulation in S. hystrix and S. pistillata. Hsp32 was up-regulated in all four species following bleaching, indicative of elevated oxidative stress. Overall, the protein expression profiles of each species contribute to assess the role of Hsps in regulating the susceptibility to thermal stresses of the various coral taxa of the Red Sea. [ABSTRACT FROM AUTHOR]

White plague disease has caused widespread coral mortality and affects over 30 Caribbean coral species, yet how different coral species respond to disease exposure has not been tested experimentally. This study quantified white plague transmission from Orbicella franksi to three susceptible and abundant coral species in the U.S. Virgin Islands: Orbicella annularis, Siderastrea siderea, and Porites astreoides. White plague was observed in 83% of tested O. annularis corals within 5.8 ± 1.1 (mean ± SE) d, 42% of S. siderea corals within 9.1 ± 1.4 d, and 17% of P. astreoides corals within 12 ± 0.87 d. Results from this study indicate that: (1) O. annularis is significantly more susceptible to white plague than S. siderea and P. astreoides, and (2) white plague infection occurs more rapidly in O. annularis than in P. astreoides. These results are important for understanding how multi-species diseases may impact coral species assemblages. [ABSTRACT FROM AUTHOR]

High temperatures disrupt coral–algal symbioses in multiple ways, with negative impacts on the physiology of the coral host, the algal symbiont, and the combined holobiont. Most heat stress studies on hard corals have understandably focused on species trends based on the combined observation of multiple individuals to account for phenotypic plasticity among colonies. As the "average coral" continues to decline while sea temperatures rise, the outlier colonies that exhibit neutral or positive responses to heat stress are coming to represent larger proportions of marginal coral populations. These colonies are those most likely to guide the future trajectory of reef ecosystems, but their dynamics are often obscured by aggregate analyses. To directly measure and analyze intraspecific variation in heat stress responses within a natural coral population, we performed aquarium experiments on sixteen colonies of the structurally important branching coral Montipora digitata from Okinawa Island, Japan. We resolved host and symbiont genotypes, exposed replicate coral fragments to ambient or elevated temperature, and monitored stress-driven differences in host calcification, symbiont photochemistry, and colony mortality. Over the 6-month experiment, six colonies appeared to tolerate stress (exhibiting no major physiological changes), seven were sensitive to stress (exhibiting reduced growth), and three expired. Both host and symbiont genotype contributed to this variation. These results demonstrate the degree to which unique M. digitata holobionts may differentially respond to thermal stress in warming oceans and highlight the important role of intraspecific variation in shaping future reef assemblages. [ABSTRACT FROM AUTHOR]

Coral reefs are under extreme threat due to a number of stressors, but temperature increases due to changing climate are the most severe. Rising ocean temperatures coupled with local extremes lead to extensive bleaching, where the coral‐algal symbiosis breaks down and corals may die, compromising the structure and function of reefs. Although the symbiotic nature of the coral colony has historically been a focus of research on coral resilience, the host itself is a foundational component in the response to thermal stress. Fixed effects in the coral host set trait baselines through evolutionary processes, acting on many loci of small effect to create mosaics of thermal tolerance across latitudes and individual coral reefs. These genomic differences can be strongly heritable, producing wide variation among clones of different genotypes or families of a specific larval cross. Phenotypic plasticity is overlaid on these baselines and a growing body of knowledge demonstrates the potential for acclimatization of reef‐building corals through a variety of mechanisms that promote resilience and stress tolerance. The long‐term persistence of coral reefs will require many of these mechanisms to adjust to warmer temperatures within a generation, bridging the gap to reproductive events that allow recombination of standing diversity and adaptive change. Business‐as‐usual climate scenarios will probably lead to the loss of some coral populations or species in the future, so the interaction between intragenerational effects and evolutionary pressure is critical for the survival of reefs. [ABSTRACT FROM AUTHOR]

Summary: Reef‐building corals form associations with a huge diversity of microorganisms, which are essential for the survival and well‐being of their host. While the acquisition patterns of Symbiodiniaceae microalgal endosymbionts are strongly linked to the coral's reproductive strategy, few studies have investigated the transmission mode of bacteria, especially in brooding species. Here, we relied on 16S rRNA gene and Internal Transcribed Spacer 2 marker metabarcoding in conjunction with fluorescence in situ hybridisation microscopy to describe the onset of microbial associations in the common brooding coral Pocillopora acuta. We analysed the bacterial and Symbiodiniaceae community composition in five adult colonies, their larvae, and 4‐day old recruits. Larvae and recruits inherited Symbiodiniaceae, as well as a small number of bacterial strains, from their parents. Rhodobacteraceae and Endozoicomonas were among the most abundant taxa that were likely maternally transmitted to the offspring. The presence of bacterial aggregates in newly released larvae was observed with confocal microscopy, confirming the occurrence of vertical transmission of bacteria in P. acuta. We concluded that host factors, as well as the environmental bacterial pool influenced the microbiome of P. acuta. [ABSTRACT FROM AUTHOR]

Reef‐building corals depend upon a nutritional endosymbiosis with photosynthetic dinoflagellates of the family Symbiodiniaceae for the majority of their energetic needs. While this mutualistic relationship is impacted by numerous stressors, warming oceans are a predominant threat to coral reefs, placing the future of the world's reefs in peril. Some Symbiodiniaceae species exhibit tolerance to thermal stress, but the in hospite symbiont response to thermal stress is underexplored. To describe the underpinnings of symbiosis and heat stress response, we compared in hospite and free‐living transcriptomes of Durusdinium trenchii, a pan‐tropical heat‐tolerant Symbiodiniaceae species, under stable temperature conditions and acute hyperthermal stress. We discovered that symbiotic state was a larger driver of the transcriptional landscape than heat stress. The majority of differentially expressed transcripts between in hospite and free‐living cells were downregulated, suggesting the in hospite condition is associated with the shutdown of numerous processes uniquely required for a free‐living lifestyle. In the free‐living state, we identified enrichment for numerous cell signalling pathways and other functions related to detecting and responding to a changing environment, as well as transcripts relating to mitosis, meiosis, and motility. In contrast, in hospite cells exhibited enhanced transcriptional activity for photosynthesis and carbohydrate transport as well as chromatin modifications and a disrupted circadian clock. Hyperthermal stress induced drastic alteration of transcriptional activity in hospite, suggesting symbiotic engagement with the host elicited an exacerbated stress response when compared to free‐living D. trenchii. Altogether, the dramatic differences in gene expression between in hospite and free‐living D. trenchii indicate the importance of considering symbiotic state in investigations of symbiosis and hyperthermal stress in Symbiodiniaceae. [ABSTRACT FROM AUTHOR]

Coral reefs represent the most diverse marine ecosystem on the planet, yet they are undergoing an unprecedented decline due to a combination of increasing global and local stressors. Despite the wealth of research investigating these stressors, Artificial Light Pollution at Night (ALAN) or "ecological light pollution" represents an emerging threat that has received little attention in the context of coral reefs, despite the potential of disrupting the chronobiology, physiology, behavior, and other biological processes of coral reef organisms. Scleractinian corals, the framework builders of coral reefs, depend on lunar illumination cues to synchronize their biological rhythms such as behavior, reproduction and physiology. While, light pollution (POL) may mask and lead de‐synchronization of these biological rhythms process. To reveal if ALAN impacts coral physiology, we have studied two coral species, Acropora eurystoma and Pocillopora damicornis, from the Gulf of Eilat/Aqaba, Red Sea, which is undergoing urban development that has led to severe POL at night. Our two experimental design data revealed that corals exposed to ALAN face an oxidative stress condition, show lower photosynthesis performances measured by electron transport rate (ETR), as well as changes in chlorophyll and algae density parameters. Testing different lights such as Blue LED and White LED spectrum showed more extreme impact in comparison to Yellow LEDs on coral physiology. The finding of this work sheds light on the emerging threat of POL and the impacts on the biology and ecology of Scleractinian corals, and will help to formulate specific management implementations to mitigate its potentially harmful impacts. [ABSTRACT FROM AUTHOR]

Climate change is the greatest threat to coral reef ecosystems. Importantly, gradual changes in seawater chemistry compounds upon increasing temperatures leading to declines in calcification and survivorship of reef-building corals. To assess relative versus synergistic effects of warming versus ocean acidification, Acropora muricata and Acropora hyacinthus were subjected to three temperature treatments (26 °C, 28.5 °C, 31 °C) crossed with three levels of pCO2 (410 μatm, 652 μatm, 934 μatm), representing current, mid and end-of-century scenarios for 12 weeks. Temperature increased gradually in the tanks from 26 °C to target temperatures over 5 weeks. Once stress was evident in the 31 °C (+ 2.5 °C above historical summer max) tanks, water temperature was decreased to normal summertime levels (29 °C) to assess recovery. pCO2 was gradually changed from control values (410 μatm) to target values over a 3 week period where they remained constant until the end of the experiment at 12 weeks. Temperature stress (31 °C) significantly impacted survivorship (90–95% decline), and over the long-term, there was a 50–90% decline in calcification across both coral species. Negative effects of mid and end-of-century pCO2 were largely independent of temperature and caused moderate reductions (36–74%) in calcification rates compared to temperature, over the long-term. Corals that survived temperature stress had higher lipid and protein content, showing that enhanced physiological condition provides an increased capacity to tolerate adverse temperatures. This study demonstrates that given the mortality rates in response to + 2.5 °C temperature stress, warming oceans (as opposed to ocean acidification) throughout the remainder of this century poses the greatest threat to reef-building corals. [ABSTRACT FROM AUTHOR]

Host species often support a genetically diverse guild of symbionts, the identity and performance of which can determine holobiont fitness under particular environmental conditions. These symbiont communities are structured by a complex set of potential interactions, both positive and negative, between the host and symbionts and among symbionts. In reef‐building corals, stable associations with specific symbiont species are common, and we hypothesize that this is partly due to ecological mechanisms, such as succession and competition, which drive patterns of symbiont winnowing in the initial colonization of new generations of coral recruits. We tested this hypothesis using the experimental framework of the de Wit replacement series and found that competitive interactions occurred among symbionts which were characterized by unique ecological strategies. Aposymbiotic octocoral recruits within high‐ and low‐light environments were inoculated with one of three Symbiodiniaceae species as monocultures or with cross‐paired mixtures, and we tracked symbiont uptake using quantitative genetic assays. Priority effects, in which early colonizers excluded competitive dominants, were evidenced under low light, but these early opportunistic species were later succeeded by competitive dominants. Under high light, a more consistent competitive hierarchy was established in which competitive dominants outgrew and limited the abundance of others. These findings provide insight into mechanisms of microbial community organization and symbiosis breakdown and recovery. Furthermore, transitions in competitive outcomes across spatial and temporal environmental variation may improve lifetime host fitness. [ABSTRACT FROM AUTHOR]

Successful reproductive output and recruitment is crucial to coral persistence and recovery following anthropogenic stress. Feeding is known to alter coral physiology and increase resilience to bleaching.The goal of the study was to address the knowledge gap of the influence of feeding on reproductive output and offspring phenotype.Colonies of Stylophora pistillata from the Northern Gulf of Aqaba (Red Sea) were fed an Artemia diet or unfed for 5 months during gametogenesis, fertilization, and brooding. In addition, time to settlement and mortality of planulae were assessed at water temperatures ranging from winter temperature (22°C) to three degrees above average peak summer temperature (31°C). A range of physiological parameters was measured in parents and offspring.In brooding parents, feeding significantly increased protein concentration and more than tripled the number of released planulae. Planulae from unfed colonies had higher chlorophyll per symbiont concentration and concomitantly higher photosynthetic efficiency compared to planulae from fed parents. In settlement assays, planulae showed a similar thermal resistance as known for this Red Sea adult population. Mortality was greater in planulae from unfed parents at ambient and 3°C above ambient temperature despite higher per offspring investment in terms of total fatty acid content. Fatty acid profiles and relative abundances were generally conserved between different fed and unfed colonies but planulae were enriched in monounsaturated fatty acids relative to adults, that is, 16:1, 18:1, 20:1, 22:1, and 24:1 isomers.Ultimately the availability of zooplankton could influence population physiology and recruitment in corals. [ABSTRACT FROM AUTHOR]

Scleractinian corals are bathed in a sea of planktonic and particle‐associated microorganisms. The metabolic products of corals influence the growth and composition of microorganisms, but interactions between corals and seawater microorganisms are underexplored. We conducted a field‐based survey to compare the biomass, diversity, composition, and functional capacity of microorganisms in small‐volume seawater samples collected adjacent to five coral species with seawater collected > 1 m away from the reef substrate on the same reefs. Seawater collected close to corals generally harbored copiotrophic‐type bacteria and its bacterial and archaeal composition was influenced by coral species as well as the local reef environment. Trends in picoplankton abundances were variable and either increased or decreased away from coral colonies based on coral species and picoplankton functional group. Genes characteristic of surface‐attached and potentially virulent microbial lifestyles were enriched in near‐coral seawater compared to reef seawater. There was a prominent association between the coral Porites astreoides and the coral symbiont Endozoicomonas, suggesting recruitment and/or shedding of these cells into the surrounding seawater. This evidence extends our understanding of potential species‐specific and reef site‐influenced microbial interactions that occur between corals and microorganisms within this near‐coral seawater environment that we propose to call the "coral ecosphere." Microbial interactions that occur within the coral ecosphere could influence recruitment of coral‐associated microorganisms and facilitate the transfer of coral metabolites into the microbial food web, thus fostering reef biogeochemical cycling and a linkage between corals and the water column. [ABSTRACT FROM AUTHOR]

The ability of massive corals to record the impacts of marine heat wave events provides a unique perspective into the variable responses of corals to anthropogenic climate change. In this study, coral cores (Porites spp.) were collected from seven reef sites across the inner‐, mid‐, and outer‐NW shelf of Australia, to examine seasonal patterns of trace element (TE), Sr/Ca and Li/Mg ratios, and extension rate signatures associated with past marine heat waves in the region. TE anomalies and declines in linear extension rate were observed in the records during the late 1990s (two of five records) and more recently during the summers of 2011 (three of seven records) and 2013 (five of seven records), indicating the impacts of marine heat waves have become increasingly widespread in the region. However, for the summers of 2011 and 2013, no significant relationships were observed between the magnitude of these TE ratio anomalies in the core records and maximum thermal stresses predicted at the reef sites from high‐resolution satellite records. We show that the strongest individual reductions in linear extension rates and associated TE ratio anomalies occurred during the 2011 heat wave, rather than during the subsequent and more intense (~1 °C warmer) 2013 event. Together, these observations suggest that at the local reef scale, Porites spp. colonies and their symbionts exhibit differential responses to heat wave events, with the prior exposure to less intense events probably playing an important role in acclimatization. Key Points: Trace element (Sr/Ca and Li/Mg) and linear extension records from Porites cores show distinct coupled signatures of past thermal stressReduced magnitude of trace element anomalies during more severe heat wave event provides new evidence of thermal acclimatisationSignificant inter‐colony relationships between the magnitude of trace element anomalies and linear extension rates [ABSTRACT FROM AUTHOR]

It is well-known that the adaptability of coral-Symbiodiniaceae symbiosis to thermal stress varies among coral species, but the cause and/or mechanism behind it are not well-understood. In this study, we aimed to explore this issue based on zooxanthellae density (ZD) and Symbiodiniaceae genus/subclade. Hemocytometry and next-generation sequencing of the internal transcribed spacer region 2 (ITS2) marker gene were used to observe ZDs and Symbiodiniaceae genera/subclades associated with 15 typical coral species in the southern South China Sea (SCS). Average ZDs of all corals were in low levels, ranging from 0.84 to 1.22 × 106 cells cm−2, with a total of five Symbiodiniaceae genera, Symbiodinium, Cladocopium, Durusdinium, Fugacium , and Gerakladium , as well as 24 dominant subclades, were detected and varied among these coral species. Pocillopora verrucosa was dominated by Durusdinium (subclade D1/D1a), and other colonial corals were dominated by Cladocopium , but the subclades were varied among these species. Porites lutea and Montipora efflorescens were dominated by C15, and Echinopora lamellosa, Hydnophora exesa , and Coscinaraea exesa were dominated by C40. Acropora corymbosa, Merulina ampliata , and five species of Faviidae were mainly associated with Cladocopium types of C3u and Cspc. In contrast to other colonial corals, the dominant subclade of solitary Fungia fungites was C27, with high host specificity. Our study indicates that coral thermal stress adaptability is mainly affected by dominant Symbiodiniaceae type instead of ZD in the southern SCS. Some heat-sensitive corals, such as P. verrucosa corals, have acquired a high abundance of heat-tolerant Durusdinium to adapt to thermal stress. This could be the main reason for these corals becoming the dominant corals in this reef region. Background subclades analyses showed significant differences among coral species in subclade quantity and diversity. These suggest that numbers of coral species may have adapted to high environmental temperature by adopting various symbionts and/or associating with heat-tolerant Symbiodiniaceae. [ABSTRACT FROM AUTHOR]

The flexibility of symbiosis establishment between the corals Platygyra acuta and Acropora valida with the dinoflagellate Symbiodinium was examined. Planula larvae of these species were provided with homologous and heterologous sources of Symbiodinium C1 and Symbiodinium D8-12. These larvae were able to acquire symbionts prior to settlement and form symbiosis with both symbiont types from all sources, revealing flexibility of symbiosis establishment at this early stage of development. No significant difference in infection percentages was found among different sources of Symbiodinium C1, suggesting that host source of the symbiont types was unimportant. Symbiodinium D8-12 resulted in significantly higher infection rates in both species. While the advantage of hosting this heterologous symbiont type in coral larvae is unclear, this may simply be a result of the infectious nature of the clade D symbiont, rather than a selection choice of the host larvae. Settlement behavior of planula larvae of P. acuta did not depend upon their status of being symbiotic or aposymbiotic. Longer term post-settlement monitoring of the growth and survival of coral larvae may provide more insight on the benefits provided by earlier uptake of symbionts and also the hosting of clade D symbiont during pre-settlement stage of the larvae. [ABSTRACT FROM AUTHOR]

Aim: The aim of the study was to assess the diversity of algal symbionts of the family Symbiodiniaceae associated with the coral genus Porites in the Red Sea, and to test for host‐specificity and environmental variables driving biogeographical patterns of algal symbiont distribution. Location: Saudi Arabian Red Sea. Taxon: Endosymbiotic dinoflagellates of the family Symbiodiniaceae in association with the reef‐building coral genus Porites. Methods: Eighty Porites coral specimens were collected along the Saudi Arabian Red Sea coast. Species boundaries were assessed morphologically and genetically (putative Control Region – mtCR; ITS region – ITS). Community composition of symbiotic dinoflagellates of the family Symbiodiniaceae was also assessed. Using the ITS2 marker with the SymPortal framework, Symbiodiniaceae data at the genus, majority ITS2 sequence and ITS2 type profile were used to assess symbiont diversity and distribution patterns. These were analysed in relation to coral host diversity, geographic location and environmental variables. Results: Among the 80 Porites samples, 10 morphologies were identified. These corals were clustered into five lineages (clades I–V) by each of the markers independently. Clades I, II and III each comprised of a single Porites morphology, while clades IV and V contained up to five distinct morphologies. The diversity of Symbiodiniaceae associated with Porites was high and latitudinal differentiation was observed. In particular, a shift from a Cladocopium‐dominated to a Durusdinium‐dominated community was found along the north–south gradient. Symbiont diversity showed the patterns of geographic‐specific association at Symbiodiniaceae genus, majority ITS2 sequence and ITS2 type profile level. Specific associations with host genotypes (but not morphological species) were also recovered when considering Symbiodiniaceae majority ITS2 sequence and ITS2 type profiles. Main conclusions: This study provides the first large‐scale molecular characterization of Symbiodiniaceae communities associated with Porites corals from the Saudi Arabian Red Sea. The use of intragenomic diversity data enabled the resolution of host‐symbiont specificity and biogeographical patterns of distribution, previously unachievable with the ITS2 marker alone. Finally, correlation among symbiont diversity and Red Sea environmental gradients was documented. [ABSTRACT FROM AUTHOR]

The global loss and degradation of coral reefs, as a result of intensified frequency and severity of bleaching events, is a major concern. Evidence of heat stress affecting corals through loss of symbionts and consequent coral bleaching was first reported in the 1930s. However, it was not until the 1998 major global bleaching event that the urgency for heat stress studies became internationally recognized. Current efforts focus not only on examining the consequences of heat stress on corals but also on finding strategies to potentially improve thermal tolerance and aid coral reefs survival in future climate scenarios. Although initial studies were limited in comparison with modern technological tools, they provided the foundation for many of today's research methods and hypotheses. Technological advancements are providing new research prospects at a rapid pace. Understanding how coral heat stress studies have evolved is important for the critical assessment of their progress. This review summarizes the development of the field to date and assesses avenues for future research. [ABSTRACT FROM AUTHOR]

Over half of all extant stony corals (Cnidaria: Anthozoa: Scleractinia) harbour endosymbiotic dinoflagellates of the family Symbiodiniaceae, forming the foundational species of modern shallow reefs. However, whether these associations are conserved on the coral phylogeny remains unknown. Here we aim to characterise Symbiodiniaceae communities in eight closely-related species in the genera Merulina, Goniastrea and Scapophyllia, and determine if the variation in endosymbiont community structure can be explained by the phylogenetic relatedness among hosts. We perform DNA metabarcoding of the nuclear internal transcribed spacer 2 using Symbiodiniaceaespecific primers on 30 coral colonies to recover three major endosymbiont clades represented by 23 distinct types. In agreement with previous studies on Southeast Asian corals, we find an abundance of Cladocopium and Durusdinium, but also detect Symbiodinium types in three of the eight coral host species. Interestingly, differences in endosymbiont community structure are dominated by host variation at the intraspecific level, rather than interspecific, intergeneric or among-clade levels, indicating a lack of phylogenetic constraint in the coral-endosymbiont association among host species. Furthermore, the limited geographic sampling of four localities spanning the Western and Central Indo-Pacific preliminarily hints at large-scale spatial structuring of Symbiodiniaceae communities. More extensive collections of corals from various regions and environments will help us better understand the specificity of the coral-endosymbiont relationship. [ABSTRACT FROM AUTHOR]

The bacterial and microalgal endosymbiont (Symbiodiniaceae spp.) communities associated with corals have important roles in their health and resilience, yet little is known about the factors driving their succession during early coral life stages. Using 16S rRNA gene and ITS2 metabarcoding, we compared these communities in four Acropora coral species and their hybrids obtained from two laboratory crosses (Acropora tenuis × Acropora loripes and Acropora sarmentosa × Acropora florida) across the parental, recruit (7 months old) and juvenile (2 years old) life stages. We tested whether microbiomes differed between (a) life stages, (b) hybrids and purebreds, and (c) treatment conditions (ambient/elevated temperature and pCO2). Microbial communities of early life stage corals were highly diverse, lacked host specificity and were primarily determined by treatment conditions. Over time, a winnowing process occurred, and distinct microbial communities developed between the two species pair crosses by 2 years of age, irrespective of hybrid or purebred status. These findings suggest that the microbial communities of corals have a period of flexibility prior to adulthood, which can be valuable to future research aimed at the manipulation of coral microbial communities. [ABSTRACT FROM AUTHOR]

Coral reef is a massive natural building block that mainly composed of hard coral. In ecological view coral reef is the center of biological activity for shelter, foraging and feeding place. Porites lutea is a common coral in reef flat area such as in Pantai Kondang Merak. This coral can form a massive with hillocky colony surface and has a slow linear extension rate, that made this coral has long longevity. The annual growth band of coral skeleton provide information of pollutants in the coastal extending back over several years ago due to ability of coral aragonite traped trace metal from environment. The aim of this research was to determine the concentration of trace metals of Cd, Cu and As along with the coral annual banding. The heavy metals detection was performed using ICP-OES (iCAP 7400 Series). The concentration of Cd, Cu and As in sample 1 (KM1) were 2.236 mg/kg, 9.726 mg/kg, and 2.474 mg/kg, while sample 2 (KM2) were 1.989 mg/kg, 19.157 mg/kg, and 2,064 mg/kg respectively. Two ways mechanism of trace metals to be trapped in the coral skeleton are by direct mechanism when trace metals in a form dissolved ion that were uptaken by coral then stored into coral skeleton and by indirect mechanism when particulate metals ingested by plankton then eaten by coral through coral tissue. The tracing of heavy metal in coral is provided important information of environment condition of the sea from 2009 - 2015 that may be used for authority decision regarding pollutant ambient in the sea environment. [ABSTRACT FROM AUTHOR]

Climate change threatens many marine ecosystems, including coral reefs and the thousands of organisms that inhabit these reefs. Fluctuations in sea surface temperatures trigger bleaching events in coral colonies that lead to increased coral mortality and reef degradation. To combat the decline in coral cover, many researchers have focused on transplanting coral colonies to better understand which species are best adapted to these environmental changes. This current study examined the impacts of two consecutive thermal stress events on transplanted coral colonies in the middle Florida Keys within the Florida Keys National Marine Sanctuary. Coral fragments of two species (Porites astreoides and Siderastrea siderea) were transplanted on seven reef sites. Transplanted colonies were monitored for evidence of coral bleaching during quarterly sampling trips from June 2013 through June 2017. Bleaching was only observed during the late summer of 2014 and 2015 when Degree Heating Weeks exceeded 4 °C-weeks. Results indicate that P. astreoides colonies had significantly higher bleaching than S. siderea colonies. Reefs differed in their proportion of bleached and unbleached corals for P. asteroides, but these reefs did not differ in their average daily maximum temperature or Degree Heating Weeks. However, individual corals that did bleach had a higher average fleshy algal abundance (Dictyota spp.) surrounding them than those corals that remained unbleached. Corals that bleached the first year and survived were no more or less likely to bleach the second year. These findings suggest that resilience to bleaching differs not only by coral species but may also be influenced by the local abundance of fleshy algal species. [ABSTRACT FROM AUTHOR]

Studying scleractinian coral bleaching and recovery dynamics in remote, isolated reef systems offers an opportunity to examine impacts of global reef stressors in the absence of local human threats. Reefs in the Chagos Archipelago, central Indian Ocean, suffered severe bleaching and mortality in 2015 following a 7.5 maximum degree heating weeks (DHWs) thermal anomaly, causing a 60% coral cover decrease from 30% cover in 2012 to 12% in April 2016. Mortality was taxon specific, with Porites becoming the dominant coral genus post-bleaching because of an 86% decline in Acropora from 14 to 2% cover. Spatial heterogeneity in Acropora mortality across the Archipelago was significantly negatively correlated with variation in DHWs and with chlorophyll-a concentrations. In 2016, a 17.6 maximum DHWs thermal anomaly caused further damage, with 68% of remaining corals bleaching in May 2016, and coral cover further declining by 29% at Peros Banhos Atoll (northern Chagos Archipelago) from 14% in March 2016 to 10% in April 2017. We therefore document back-to-back coral bleaching and mortality events for two successive years in the remote central Indian Ocean. Our results indicate lower coral mortality in 2016 than 2015 despite a more severe thermal anomaly event in 2016. This could be caused by increased thermal resistance and resilience within corals surviving the 2015 thermal anomaly; however, high bleaching prevalence in 2016 suggests there remained a high sensitivity to bleaching. Similar coral mortality and community change were seen in the Chagos Archipelago following the 1998 global bleaching event, from which recovery took 10 yr. This relatively rapid recovery suggests high reef resiliency and indicates that the Archipelago's lack of local disturbances will increase the probability that the reefs will again recover over time. However, as the return time between thermal anomaly events becomes shorter, this ability to recover will become increasingly compromised. [ABSTRACT FROM AUTHOR]

Thermal stress is a major contributor to loss of coral cover, significantly impacting reefs during the third global bleaching event between 2014 and 2017. The long-term persistence of coral reefs depends on acclimatization and adaptation to changing climate, which are influenced greatly by the interactions between bleaching and reproductive success. We observed a genotypically diverse population of Orbicella faveolata before, during, and after consecutive bleaching events in 2014 and 2015 in the Florida Keys. We documented less bleaching during the second event despite 40% more time above local bleaching thresholds and an association between bleaching severity and subsequent spawning. Approximately 75% of colonies experienced the same or less severe bleaching in the second event despite being metabolically compromised, with a substantial minority (~ 35%) faring better in the second event. The second bleaching event also resulted in smaller decreases in chlorophyll content per symbiont cell and symbiont-to-host cell ratio reef-wide, representing less damage to the coral–algal symbiosis. All colonies that recovered quickly (~ 1 month) or did not bleach in 2014 released gametes in 2015, while only 60% of colonies that recovered more slowly did. Bleaching also impacted the amount of gametes released, with more severe bleaching significantly associated with gamete release from < 50% of the colony surface area. Bleaching and spawning outcomes were supported by dynamic physiological changes during bleaching and recovery. Lipid concentration and symbiont-to-host cell ratios collected from the bottom edge of the colony in the middle of the recovery period (February and April) were most important for predicting spawning the following year, highlighting the dynamic interaction between micro-habitats and time in recovery and gametogenesis. This study finds signals of physiological acclimatization in an important reef-building coral and underscores the importance of recovery post-bleaching and reproduction for the persistence of coral reefs. [ABSTRACT FROM AUTHOR]

Ocean warming is negatively impacting coral reef ecosystems and considerable effort is currently invested in projecting coral reef futures under 21st century climate change. A limiting factor in these projections is lack of quantitative data on the thermal thresholds of different reef communities, due in large part to spatial and temporal gaps in bleaching observations. Here we apply a coral bleaching proxy, skeletal stress bands, to reconstruct the history of bleaching on eight coral reefs in the central equatorial Pacific (CEP) and use this information to constrain the thermal thresholds of their coral communities. First, three genera of massive corals collected on both Pacific and Caribbean reefs are used to derive a calibration between the proportion of corals that form stress bands during a bleaching event, and the total observed bleaching incidence in the community of mixed coral taxa. The correlation is highly significant, indicating that stress bands in massive corals reflect community-level bleaching severity (R2 = 0.945, p < 0.001). We applied the calibration to stress band records from eight Pacific reefs, reconstructing their bleaching histories over the period 1982 to 2015. A percentile-based method of estimating thermal stress (Degree Heating Weeks) for CEP reefs was developed and applied. Comparing the level of thermal stress experienced by each coral community during each event with the reconstructed bleaching response, we characterized the thermal sensitivities of each reef community and quantified the thermal threshold (b½) at which 50% of the coral community bleached. Our analysis reveals a unique non-linear thermal response curve for each reef. The most thermally tolerant reefs in the study (Jarvis and Kanton Islands) experienced 50% bleaching at seven to nine times more thermal stress than did the least resistant reef in the study (Maiana Island). An exploration of the potential drivers of thermal tolerance revealed a strong correlation between b½ and the history of thermal stress events in each reef system. Thermal tolerance was also correlated with concentrations of dissolved inorganic nitrate in the water column and with estimates of coral energetic reserve. [ABSTRACT FROM AUTHOR]

Concomitant to the decline of tropical corals caused by increasing global sea temperatures is the potential removal of barriers to species range expansions into subtropical and temperate habitats. In these habitats, species must tolerate lower annual mean temperature, wider annual temperature ranges and lower minimum temperatures. To understand ecophysiological traits that will impact geographical range boundaries, we monitored populations of five coral species within a marginal habitat and used a year of in situ measures to model thermal performance of vital host, symbiont and holobiont physiology. Metabolic responses to temperature revealed two acclimatization strategies: peak productivity occurring at annual midpoint temperatures (4–6°C lower than tropical counterparts), or at annual maxima. Modelled relationships between temperature and P:R were compared to a year of daily subtropical sea temperatures and revealed that the relatively short time spent at any one temperature, limited optimal performance of all strategies to approximately half the days of the year. Thus, while subtropical corals can adjust their physiology to persist through seasonal lows, seasonal variation seems to be the key factor limiting coral productivity. This constraint on rapid reef accretion within subtropical environments provides insight into the global distribution of future coral reefs and their ecosystem services. [ABSTRACT FROM AUTHOR]

Unlike most bivalve shellfishes, giant clams (tridacnines) harbor symbiotic microalgae (zooxanthellae) in their fleshy bodies. Zooxanthellae are not maternally inherited by tridacnine offspring, hence, the larvae must acquire zooxanthellae from external sources, although such algal populations or sources in the environment are currently unknown. It is well known that giant clams expel fecal pellets that contain viable zooxanthellae cells, but whether these cells are infectious or just an expelled overpopulation from the giant clams has not been investigated. In this study, we observed the ultrastructural and photosynthetic competencies of zooxanthellae in the fecal pellets of Tridacna crocea and further tested the ability of these cells to infect T. squamosa juveniles. The ultrastructure of the zooxanthellae cells showed that the cells were intact and had not undergone digestion. Additionally, these zooxanthellae cells showed a maximum quantum yield of photosystem II (Fv/Fm) as high as those retained in the mantle of the giant clam. Under the assumption that feces might provide symbionts to the larvae of other giant clams, fecal pellets from Tridacna squamosa and T. crocea were given to artificially hatched 1-day-old T. squamosa larvae. On the 9th day, 15–34% of the larvae provided with the fecal pellets took up zooxanthellae in their stomach, and on the 14th day, zooxanthellae cells reached the larval margin, indicating the establishment of symbiosis. The rate reaching this stage was highest, ca. 5.3%, in the larvae given whole (nonhomogenized) pellets from T. crocea. The composition of zooxanthellae genera contained in the larvae were similar to those in the fecal pellets, although the abundance ratios were significantly different. This study is the first to demonstrate the potential of giant clam fecal pellets as symbiont vectors to giant clam larvae. These results also demonstrate the possibility that fecal pellets are a source of zooxanthellae in coral reefs. [ABSTRACT FROM AUTHOR]

As the Earth's temperature continues to rise, coral bleaching events become more frequent. Some of the most affected reef ecosystems are located in poorly monitored waters, and thus, the extent of the damage is unknown. We propose the use of marine heatwaves (MHWs) as a new approach for detecting coral reef zones susceptible to bleaching, using the Red Sea as a model system. Red Sea corals are exceptionally heat‐resistant, yet bleaching events have increased in frequency. By applying a strict definition of MHWs on >30 year satellite‐derived sea surface temperature observations (1985–2015), we provide an atlas of MHW hotspots over the Red Sea coral reef zones, which includes all MHWs that caused major coral bleaching. We found that: (a) if tuned to a specific set of conditions, MHWs identify all areas where coral bleaching has previously been reported; (b) those conditions extended farther and occurred more often than bleaching was reported; and (c) an emergent pattern of extreme warming events is evident in the northern Red Sea (since 1998), a region until now thought to be a thermal refuge for corals. We argue that bleaching in the Red Sea may be vastly underrepresented. Additionally, although northern Red Sea corals exhibit remarkably high thermal resistance, the rapidly rising incidence of MHWs of high intensity indicates this region may not remain a thermal refuge much longer. As our regionally tuned MHW algorithm was capable of isolating all extreme warming events that have led to documented coral bleaching in the Red Sea, we propose that this approach could be used to reveal bleaching‐prone regions in other data‐limited tropical regions. It may thus prove a highly valuable tool for policymakers to optimize the sustainable management of coastal economic zones. [ABSTRACT FROM AUTHOR]

We present SymPortal (SymPortal.org), a novel analytical framework and platform for genetically resolving the algal symbionts of reef corals using next‐generation sequencing (NGS) data of the ITS2 rDNA. Although the ITS2 marker is widely used to genetically characterize taxa within the family Symbiodiniaceae (formerly the genus Symbiodinium), the multicopy nature of the marker complicates its use. Commonly, the intragenomic diversity resultant from this multicopy nature is collapsed by analytical approaches, thereby focusing on only the most abundant sequences. In contrast, SymPortal employs logic to identify within‐sample informative intragenomic sequences, which we have termed 'defining intragenomic variants' (DIVs), to identify ITS2‐type profiles representative of putative Symbiodiniaceae taxa. By making use of this intragenomic ITS2 diversity, SymPortal is able to resolve genetic delineations using the ITS2 marker at a level that was previously only possible by using additional genetic markers. We demonstrate this by comparing this novel approach to the most commonly used alternative approach for NGS ITS2 data, the 97% similarity clustering to operational taxonomic units (OTUs). The SymPortal platform accepts NGS raw sequencing data as input to provide an easy‐to‐use, standardization‐enforced, and community‐driven framework that integrates with a database to gain resolving power with increased use. We consider that SymPortal, in conjunction with ongoing large‐scale sampling and sequencing efforts, should play an instrumental role in making future sampling efforts more comparable and in maximizing their efficacy in working towards the classification of the global Symbiodiniaceae diversity. [ABSTRACT FROM AUTHOR]

The Symbiodinaceae are paradoxical in that they play a fundamental role in the success of scleractinian corals, but also in their dismissal when under stress. In the past decades, the discovery of the endosymbiont’s genetic and functional diversity has led people to hope that some coral species can survive bleaching events by associating with a stress-resistant symbiont that can become dominant when seawater temperatures increase. The variety of individual responses encouraged us to scrutinize each species individually to gauge its resilience to future changes. Here, we analyse the temporal variation in the Symbiodinaceae community associated with Leptoria phrygia, a common scleractinian coral from the Indo-Pacific. Coral colonies were sampled from two distant reef sites located in southern Taiwan that differ in temperature regimes, exemplifying a ‘variable site’ (VS) and a ‘steady site’ (SS). We investigated changes in the relative abundance of the dominant symbiont and its physiology every 3–4 months from 2016–2017. At VS, 11 of the 12 colonies were dominated by the stress-resistant Durusdinium spp. (>90% dominance) and only one colony exhibited co-dominance between Durusdinium spp. and Cladocopium spp. Every colony displayed high photochemical efficiency across all sampling periods, while showing temporal differences in symbiont density and chlorophyll a concentration. At SS, seven colonies out of 13 were dominated by Cladocopium spp., five presented co-dominance between Durusdinium spp./Cladocopium spp. and only one was dominated by Durusdinium spp. Colonies showed temporal differences in photochemical efficiency and chlorophyll a concentration during the study period. Our results suggest that VS colonies responded physiologically better to high temperature variability by associating with Durusdinium spp., while in SS there is still inter-colonial variability, a feature that might be advantageous for coping with different environmental changes. [ABSTRACT FROM AUTHOR]

Coral reefs are continuing to decline worldwide due to anthropogenic climate change. The study of the molecular diversity and biogeographical patterns of Symbiodiniaceae, is essential to understand the adaptive potential and resilience of coral–algal symbiosis. Next generation sequencing was used to analyze the Symbiodiniaceae rDNA internal transcribed spacer 2 marker genes from 178 reef-building coral samples in eight coral habitats across approximately 13° of latitude in the South China Sea (SCS). A total of three Symbiodiniaceae genera, Cladocopium , Durusdinium , and Gerakladium , as well as 31 dominant Symbiodiniaceae types, were identified. Symbiodiniaceae richness, diversity, and community composition varied according to latitude; intermediate and low latitude coral reefs (IR and LR) have higher Symbiodiniaceae richness and diversity than high latitude coral habitats (HC and HR). A PERMANOVA analysis found significant differences in the Symbiodiniaceae community composition in the SCS (F = 14.75, R 2 = 0.20, p = 0.001 < 0.01). The major dominant Symbiodiniaceae types were C1 in the HC and the HR, C1/Cspc/C50/C15 and D1 in the IR, and C3u and C15 in the LR. Canonical correspondence analysis showed that the relative abundance of different Symbiodiniaceae types is affected by multiple environmental factors. Phylogenetic analysis indicated that the Symbiodiniaceae type Cladocopium , which shared common ancestors, shows similar environmental adaptability. Based on these results, we suggest that coral host species played a relatively small role in the identity of the dominant Symbiodiniaceae type. Therefore, the biogeographical patterns of Symbiodiniaceae may be mainly affected by environmental factors. Our research provides a comprehensive overview of the biogeography of Symbiodiniaceae in the SCS, where coral communities and reefs are widely distributed across different latitude regions and have variable environmental conditions. Our data will provide support for further study of the regional diversification of Symbiodiniaceae and the ecological resilience of the coral-Symbiodiniaceae symbioses. [ABSTRACT FROM AUTHOR]

Hydrozoans of the genus Zanclea have been acknowledged only recently as a fundamental component of the highly diverse fauna associated with reef‐building scleractinian corals. Although widely distributed in coral reefs and demonstrated to be important in protecting corals from predation and diseases, the biodiversity of these hydrozoans remains enigmatic due to the paucity of available morphological characters, incomplete morphological characterisations and the possible existence of cryptic species. Recently, molecular techniques have revealed the existence of multiple hidden genetic lineages not yet supported by diagnostic morphological characters. In this work, we further explore the morpho‐diversity of three genetic lineages, namely Zanclea associated with the coral genera Goniastrea (clade I), Porites (clade II) and Pavona (clade VI). Aside from providing a complete classical characterisation of the polyp and medusa stage of each clade, we searched for new potential taxonomic indicators either on symbiotic hydroids or on host corals. On the hydroids, statistical analyses on almost 7,000 nematocyst capsules revealed a significant difference in terms of nematocyst size among the three Zanclea clades investigated. On each host coral genus, we identified peculiar skeletal modifications related to the presence of Zanclea symbionts. Lastly, we discussed the potential diagnostic value of these footprints in the characterisation of Zanclea–scleractinian associations. [ABSTRACT FROM AUTHOR]

Aim: Predicting species distributional shifts in future climate scenarios representing conditions that do not exist in the current world is a challenge. Species distribution models may result in misrepresented projections for species living in extreme conditions if based on truncated response functions. Model extrapolation may not detect declines that could occur if future environment conditions exceeded the physiological tolerance of the species. We developed a novel method aimed to overcome this constrain by incorporating the physiological response function of a tropical hydrocoral to temperature as a predictor variable in a Hybrid SDM. Location: Atlantic Ocean. Methods: We conducted ecophysiological experiments simulating heat and cold stress to determine the maximum photochemical efficiency of the hydrocoral's symbiont along a thermal gradient to identify sublethal and lethal conditions. The response curve obtained was then applied to a temperature raster to create a new physio‐climatic variable, which was integrated into the Hybrid SDM as a predictor. Simple Physiological and Correlative SDMs were compared with the Hybrid model. Results: The Hybrid SDM outperformed the Correlative SDM allowing predictions without extrapolations in the physio‐climatic predictor. It suggested habitat contractions in tropical regions with forecasted temperatures above the coral's physiological tolerance, which were underrepresented by the Correlative SDM. It also incorporated habitat suitability restrictions by other predictors of unknown physiological response by incorporating correlative information (as limitations in river mouths by low salinity). In this way, by integrating mechanistic and correlative knowledge, the Hybrid SDM also predicted a potential expansion to higher latitudes, which agreed with the recent evidence of its expansion into the subtropical Canary Islands. Main conclusion: Integrating physiological knowledge into Hybrid SDMs by adding a physio‐climatic predictor improves model transferability resulting in predictions of decline in future climates, which may be misrepresented by SDMs trained at present‐day conditions, and therefore are advisable for early warning in conservation management. [ABSTRACT FROM AUTHOR]

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In Focus: Dunphy, CM, Vollmer, SV, Gouhier, TC. (2021) Host–microbial systems as glass cannons: Explaining microbiome stability in corals exposed to extrinsic perturbations. Journal of Animal Ecology, 90, 1044–1057. The importance of symbiotic microbial communities for the functioning of animal hosts is now well‐documented; however, the interactions between host microbiomes and stress are less well‐understood. Dunphy et al. used a common garden experiment to show that host–microbiomes vary in their resilience across different coral species. The authors then used mathematical modelling to provide novel evidence that species with microbiomes that are regulated by host processes are robust to perturbation from stressors, but that robustness comes at a higher cost to the host. Conversely, species with microbiomes that are regulated by microbial processes are generally much more resilient and cheaper to support, but when disrupted by external stressors, the communities break down entirely—these latter species are termed 'glass cannons'. This novel hypothesis has important implications for how host microbiomes function in a rapidly changing world that exposes animal hosts to multiple biotic and abiotic perturbations. [ABSTRACT FROM AUTHOR]

Zooxanthellate corals live in symbiosis with phototrophic dinoflagellates of the family Symbiodiniaceae, enabling the host coral to dwell in shallow, nutrient-poor marine waters. The South Atlantic Ocean is characterized by low coral diversity with high levels of endemism. However, little is known about coral–dinoflagellate associations in the region. This study examined the diversity of Symbiodiniaceae associated with the scleractinian coral Favia gravida across its distributional range using the ITS-2 marker. This brooding coral endemic to the South Atlantic can be found across a wide range of latitudes and longitudes, including the Mid-Atlantic islands. Even though it occurs primarily in shallower environments, F. gravida is among the few coral species that live in habitats with extreme environmental conditions (high irradiance, temperature, and turbidity) such as very shallow tide pools. In the present study, we show that F. gravida exhibits some degree of flexibility in its symbiotic association with zooxanthellae across its range. F. gravida associates predominantly with Cladocopium C3 (ITS2 type Symbiodinium C3) but also with Symbiodinium A3, Symbiodinium linucheae (ITS2 type A4), Cladocopium C1, Cladocopium C130, and Fugacium F3. Symbiont diversity varied across biogeographic regions (Symbiodinium A3 and S. linucheae were found in the Tropical Eastern Atlantic, Cladocopium C1 in the Mid-Atlantic, and other subtypes in the Southwestern Atlantic) and was affected by local environmental conditions. In addition, Symbiodiniaceae diversity was highest in a southwestern Atlantic oceanic island (Rocas Atoll). Understanding the relationship between corals and their algal symbionts is critical in determining the factors that control the ecological niches of zooxanthellate corals and their symbionts, and identifying host-symbiont pairs that may be more resistant to environmental changes. [ABSTRACT FROM AUTHOR]

Reef-building corals form an obligate symbiosis with photosynthetic microalgae in the family Symbiodiniaceae that meet most of their energy requirements. This symbiosis is under threat from the unprecedented rate of ocean warming as well as the simultaneous pressure of local stressors such as poor water quality. Only 1°C above mean summer sea surface temperatures (SSTs) on the Great Barrier Reef (GBR) can trigger the loss of Symbiodiniaceae from the host, and very low concentrations of the most common herbicide, diuron, can disrupt the photosynthetic activity of microalgae. In an era of rapid environmental change, investigation into the assisted evolution of the coral holobiont is underway in an effort to enhance the resilience of corals. Apicomplexan-like microalgae were discovered in 2008 and the Phylum Chromerida (chromerids) was created. Chromerids have been isolated from corals and contain a functional photosynthetic plastid. Their discovery therefore opens a new avenue of research into the use of alternative/additional photosymbionts of corals. However, only two studies to-date have investigated the symbiotic nature of Chromera velia with corals and thus little is known about the coral-chromerid relationship. Furthermore, the response of chromerids to environmental stressors has not been examined. Here we tested the performance of four chromerid strains and the common dinoflagellate symbiont Cladocopium goreaui (formerly Symbiodinium goreaui , ITS2 type C1) in response to elevated temperature, diuron and their combined exposure. Three of the four chromerid strains exhibited high thermal tolerances and two strains showed exceptional herbicide tolerances, greater than observed for any photosynthetic microalgae, including C. goreaui. We also investigated the onset of symbiosis between the chromerids and larvae of two common GBR coral species under ambient and stress conditions. Levels of colonization of coral larvae with the chromerid strains were low compared to colonization with C. goreaui. We did not observe any overall negative or positive larval fitness effects of the inoculation with chromerid algae vs. C. goreaui. However, we cannot exclude the possibility that chromerid algae may have more important roles in later coral life stages and recommend this be the focus of future studies. [ABSTRACT FROM AUTHOR]

Genotype-specific contributions to the environmental tolerance and disease susceptibility of corals are widely accepted. Yet our understanding of how host genotype influences the composition and stability of the coral microbiome subjected to environmental fluctuations is limited. To gain insight into the community dynamics and environmental stability of microbiomes associated with distinct coral genotypes, we assessed the microbial community associated with Acropora tenuis under single and cumulative pressure experiments. Experimental treatments comprised either a single pulse of reduced salinity (minimum of 28 psu) or exposure to the cumulative pressures of reduced salinity (minimum of 28 psu), elevated seawater temperature (+2 C), elevated pCO2 (900 ppm), and the presence of macroalgae. Analysis of 16S rRNA gene amplicon sequence data revealed that A. tenuis microbiomes were highly host-genotype specific and maintained high compositional stability irrespective of experimental treatment. On average, 48% of the A. tenuis microbiome was dominated by Endozoicomonas. Amplicon sequence variants (ASVs) belonging to this genus were significantly different between host individuals. Although no signs of stress were evident in the coral holobiont and the vast majority of ASVs remained stable across treatments, a microbial indicator approach identified 26 ASVs belonging to Vibrionaceae, Rhodobacteraceae, Hahellaceae, Planctomycetes, Phylobacteriaceae, Flavobacteriaceae, and Cryomorphaceae that were significantly enriched in corals exposed to single and cumulative stressors. While several recent studies have highlighted the efficacy of microbial indicators as sensitive markers for environmental disturbance, the high host-genotype specificity of coral microbiomes may limit their utility and we therefore recommend meticulous control of host-genotype effects in coral microbiome research. [ABSTRACT FROM AUTHOR]

Coral mucus is continuously released by most corals and acts as an important protective barrier and as a substrate for host-associated microbial communities due to its complex composition of carbohydrates, lipids, and proteins. On a reef scale, coral mucus functions as a particle trap, thereby retaining nutrients and energy in the ecosystem. Given the distinct environmental conditions in the Red Sea (high temperature, high salinity, high total alkalinity), we sought to investigate the carbohydrate composition of mucus from five corals from the central Red Sea. Our aim was to assess whether mucus from Red Sea corals is different from what is known from other corals and whether those differences could be aligned to putative beneficial functions with regard to the prevailing environment. Using gas chromatography/mass spectrometry, we detected nine sugars as the main prevalent carbohydrates. Although we detected significant differences between species with regard to the relative abundance of given carbohydrates, the identified sugars resembled those found in mucus from corals elsewhere, and we could corroborate high abundance of arabinose in acroporid corals. Taken together, our results suggest the presence of a common set of carbohydrates across a broad range of coral species from geographically diverse environments, highlighting the important role of mucus with regard to coral and reef ecosystem function. [ABSTRACT FROM AUTHOR]