Short-wavelength-sensitive 1 (SWS1) opsin gene duplications and parallel visual pigment tuning support ultraviolet communication in damselfishes (Pomacentridae).

Damselfishes (Pomacentridae) are one of the most behaviourally diverse, colourful and species-rich reef fish families. One remarkable characteristic of damselfishes is their communication in ultraviolet (UV) light. Not only are they sensitive to UV, they are also prone to have UV-reflective colours and patterns enabling social signalling. Using more than 50 species, we aimed to uncover the evolutionary history of UV colour and UV vision in damselfishes. All damselfishes had UV-transmitting lenses, expressed the UV-sensitive SWS1 opsin gene, and most displayed UV-reflective patterns and colours. We find evidence for several tuning events across the radiation, and while SWS1 gene duplications are generally very rare among teleosts, our phylogenetic reconstructions uncovered two independent duplication events: one close to the base of the most species-rich clade in the subfamily Pomacentrinae, and one in a single Chromis species. Using amino acid comparisons, we found that known spectral tuning sites were altered several times in parallel across the damselfish radiation (through sequence change and duplication followed by sequence change), causing repeated shifts in peak spectral absorbance of around 10 nm. Pomacentrinae damselfishes expressed either one or both copies of SWS1, likely to further finetune UV-signal detection and differentiation. This highly advanced and modified UV vision among damselfishes, in particular the duplication of SWS1 among Pomacentrinae, might be seen as a key evolutionary innovation that facilitated the evolution of the exuberant variety of UV-reflectance traits and the diversification of this coral reef fish lineage.

Coral-infecting parasites in cold marine ecosystems.

Coral reefs are a biodiversity hotspot,1,2 and the association between coral and intracellular dinoflagellates is a model for endosymbiosis.3,4 Recently, corals and related anthozoans have also been found to harbor another kind of endosymbiont, apicomplexans called corallicolids.5 Apicomplexans are a diverse lineage of obligate intracellular parasites6 that include human pathogens such as the malaria parasite, Plasmodium.7 Global environmental sequencing shows corallicolids are tightly associated with tropical and subtropical reef environments,5,8,9 where they infect diverse corals across a range of depths in many reef systems, and correlate with host mortality during bleaching events.10 All of this points to corallicolids being ecologically significant to coral reefs, but it is also possible they are even more widely distributed because most environmental sampling is biased against parasites that maintain a tight association with their hosts throughout their life cycle. We tested the global distribution of corallicolids using a more direct approach, by specifically targeting potential anthozoan host animals from cold/temperate marine waters outside the coral reef context. We found that corallicolids are in fact common in such hosts, in some cases at high frequency, and that they infect the same tissue as parasites from topical coral reefs. Parasite phylogeny suggests corallicolids move between hosts and habitats relatively frequently, but that biogeography is more conserved. Overall, these results greatly expand the range of corallicolids beyond coral reefs, suggesting they are globally distributed parasites of marine anthozoans, which also illustrates significant blind spots that result from strategies commonly used to sample microbial biodiversity.

Lipid Droplets in Endosymbiotic Symbiodiniaceae spp. Associated with Corals.

Symbiodiniaceae species is a dinoflagellate that plays a crucial role in maintaining the symbiotic mutualism of reef-building corals in the ocean. Reef-building corals, as hosts, provide the nutrition and habitat to endosymbiotic Symbiodiniaceae species and Symbiodiniaceae species transfer the fixed carbon to the corals for growth. Environmental stress is one of the factors impacting the physiology and metabolism of the corals-dinoflagellate association. The environmental stress triggers the metabolic changes in Symbiodiniaceae species resulting in an increase in the production of survival organelles related to storage components such as lipid droplets (LD). LDs are found as unique organelles, mainly composed of triacylglycerols surrounded by phospholipids embedded with some proteins. To date, it has been reported that investigation of lipid droplets significantly present in animals and plants led to the understanding that lipid droplets play a key role in lipid storage and transport. The major challenge of investigating endosymbiotic Symbiodiniaceae species lies in overcoming the strategies in isolating lesser lipid droplets present in its intercellular cells. Here, we review the most recent highlights of LD research in endosymbiotic Symbiodiniaceae species particularly focusing on LD biogenesis, mechanism, and major lipid droplet proteins. Moreover, to comprehend potential novel ways of energy storage in the symbiotic interaction between endosymbiotic Symbiodiniaceae species and its host, we also emphasize recent emerging environmental factors such as temperature, ocean acidification, and nutrient impacting the accumulation of lipid droplets in endosymbiotic Symbiodiniaceae species.

Combining environmental DNA and visual surveys can inform conservation planning for coral reefs.

Environmental DNA (eDNA) metabarcoding has the potential to revolutionize conservation planning by providing spatially and taxonomically comprehensive data on biodiversity and ecosystem conditions, but its utility to inform the design of protected areas remains untested. Here, we quantify whether and how identifying conservation priority areas within coral reef ecosystems differs when biodiversity information is collected via eDNA analyses or traditional visual census records. We focus on 147 coral reefs in Indonesia's hyper-diverse Wallacea region and show large discrepancies in the allocation and spatial design of conservation priority areas when coral reef species were surveyed with underwater visual techniques (fishes, corals, and algae) or eDNA metabarcoding (eukaryotes and metazoans). Specifically, incidental protection occurred for 55% of eDNA species when targets were set for species detected by visual surveys and 71% vice versa. This finding is supported by generally low overlap in detection between visual census and eDNA methods at species level, with more overlap at higher taxonomic ranks. Incomplete taxonomic reference databases for the highly diverse Wallacea reefs, and the complementary detection of species by the two methods, underscore the current need to combine different biodiversity data sources to maximize species representation in conservation planning.

Nutrient depletion and heat stress impair the assimilation of nitrogen compounds in a scleractinian coral.

Concentrations of dissolved nitrogen in seawater can affect the resilience of the cnidarian-dinoflagellate symbiosis to climate change-induced bleaching. However, it is not yet known how the assimilation and translocation of the various nitrogen forms change during heat stress, nor how the symbiosis responds to nutrient depletion, which may be observed due to increasing water stratification. Here, the tropical scleractinian coral Stylophora pistillata, in symbiosis with dinoflagellates of the genus Symbiodinium, was grown at different temperatures (26°C, 30°C, and 34°C), before being placed in nutrient-replete or depleted seawater for 24 hours. The corals were then incubated with 13C-labelled sodium bicarbonate and different 15N-labelled nitrogen forms (ammonium, urea, and dissolved free amino acids) to determine their assimilation rates. We found that nutrient depletion inhibited the assimilation of all nitrogen sources studied and that heat stress reduced the assimilation of ammonium and dissolved free amino acids. However, the host assimilated over threefold more urea at 30°C relative to 26°C. Overall, both moderate heat stress (30°C) and nutrient depletion individually decreased the total nitrogen assimilated by the symbiont by 66%, and combined, they decreased assimilation by 79%. This led to the symbiotic algae becoming nitrogen starved, with the C:N ratio increasing over threefold at 34°C, potentially exacerbating the impacts of coral bleaching.

A systematic review of robotic efficacy in coral reef monitoring techniques.

Coral reefs are home to a variety of species, and their preservation is a popular study area; however, monitoring them is a significant challenge, for which the use of robots offers a promising answer. The purpose of this study is to analyze the current techniques and tools employed in coral reef monitoring, with a focus on the role of robotics and its potential in transforming this sector. Using a systematic review methodology examining peer-reviewed literature across engineering and earth sciences from the Scopus database focusing on "robotics" and "coral reef" keywords, the article is divided into three sections: coral reef monitoring, robots in coral reef monitoring, and case studies. The initial findings indicated a variety of monitoring strategies, each with its own advantages and disadvantages. Case studies have also highlighted the global application of robotics in monitoring, emphasizing the challenges and opportunities unique to each context. Robotic interventions driven by artificial intelligence and machine learning have led to a new era in coral reef monitoring. Such developments not only improve monitoring but also support the conservation and restoration of these vulnerable ecosystems. Further research is required, particularly on robotic systems for monitoring coral nurseries and maximizing coral health in both indoor and open-sea settings.

Localization and symbiotic status of probiotics in the coral holobiont.

Corals establish symbiotic relationships with microorganisms, especially endosymbiotic photosynthetic algae. Although other microbes have been commonly detected in coral tissues, their identity and beneficial functions for their host are unclear. Here, we confirm the beneficial outcomes of the inoculation of bacteria selected as probiotics and use fluorescence in situ hybridization (FISH) to define their localization in the coral Pocillopora damicornis. Our results show the first evidence of the inherent presence of Halomonas sp. and Cobetia sp. in native coral tissues, even before their inoculation. Furthermore, the relative enrichment of these coral tissue-associated bacteria through their inoculation in corals correlates with health improvements, such as increases in photosynthetic potential, and productivity. Our study suggests the symbiotic status of Halomonas sp. and Cobetia sp. in corals by indicating their localization within coral gastrodermis and epidermis and correlating their increased relative abundance through active inoculation with beneficial outcomes for the holobiont. This knowledge is crucial to facilitate the screening and application of probiotics that may not be transient members of the coral microbiome. IMPORTANCE: Despite the promising results indicating the beneficial outcomes associated with the application of probiotics in corals and some scarce knowledge regarding the identity of bacterial cells found within the coral tissue, the correlation between these two aspects is still missing. This gap limits our understanding of the actual diversity of coral-associated bacteria and whether these symbionts are beneficial. Some researchers, for example, have been suggesting that probiotic screening should only focus on the very few known tissue-associated bacteria, such as Endozoicomonas sp., assuming that the currently tested probiotics are not tissue-associated. Here, we provide specific FISH probes for Halomonas sp. and Cobetia sp., expand our knowledge of the identity of coral-associated bacteria and confirm the probiotic status of the tested probiotics. The presence of these beneficial microorganisms for corals (BMCs) inside host tissues and gastric cavities also supports the notion that direct interactions with the host may underpin their probiotic role. This is a new breakthrough; these results argue against the possibility that the positive effects of BMCs are due to factors that are not related to a direct symbiotic interaction, for example, that the host simply feeds on inoculated bacteria or that the bacteria change the water quality.

Organophosphate esters (OPEs) in corals of the South China Sea: Occurrence, distribution, and bioaccumulation.

Organophosphate esters (OPEs) have garnered significant attention in recent years. In view of the enormous ecosystem services value and severe degradation of coral reefs in the South China Sea, this study investigated the occurrence, distribution, and bioaccumulation of 11 OPEs in five coral regions: Daya Bay (DY), Weizhou Island (WZ), Sanya Luhuitou (LHT), Xisha (XS) Islands, and Nansha (NS) Islands. Although OPEs were detected at a high rate, their concentration in South China Sea seawater (1.56 ± 0.89 ng L-1) remained relatively low compared to global levels. All OPEs were identified in coral tissues, with Luhuitou (575 ± 242 ng g-1 dw) showing the highest pollution levels, attributed to intense human activities. Coral mucus, acting as a defense against environmental stresses, accumulated higher ∑11OPEs (414 ± 461 ng g-1 dw) than coral tissues (412 ± 197 ng g-1 dw) (nonparametric test, p < 0.05), and their compositional characteristics varied greatly. In the case of harsh aquatic environments, corals increase mucus secretion and then accumulate organic pollutants. Tissue-mucus partitioning varied among coral species. Most OPEs were found to be bioaccumulative (BAFs >5000 L kg-1) in a few coral tissue samples besides Triphenyl phosphate (TPHP). Mucus' role in the bioaccumulation of OPEs in coral shouldn't be ignored.

A new strategy based on a cascade amplification strategy biosensor for on-site eDNA detection and outbreak warning of crown-of-thorns starfish.

Population outbreaks of the crown-of-thorns starfish (COTS) seriously threaten the sustainability of coral reef ecosystems. However, traditional ecological monitoring techniques cannot provide early warning before the outbreaks, thus preventing timely intervention. Therefore, there is an urgent need for a more accurate and faster technology to predict the outbreaks of COTS. In this work, we developed an electrochemical biosensor based on a programmed catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) cyclic amplification strategy for sensitive and selective detection of COTS environmental DNA (eDNA) in water bodies. This biosensor exhibited excellent electrochemical characteristics, including a low limit of detection (LOD = 18.4 fM), low limit of quantification (LOQ = 41.1 fM), and wide linear range (50 fM - 10 nM). The biosensing technology successfully allowed the detection of COTS eDNA in the aquarium environment, and the results also demonstrated a significant correlation between eDNA concentration and COTS number (r = 0.990; P < 0.001). The reliability and accuracy of the biosensor results have been further validated through comparison with digital droplet PCR (ddPCR). Moreover, the applicability and accuracy of the biosensor were reconfirmed in field tests at the COTS outbreak site in the South China Sea, which has shown potential application in dynamically monitoring the larvae before the COTS outbreak. Therefore, this efficient electrochemical biosensing technology offers a new solution for on-site monitoring and early warning of the COTS outbreak.

Impact of human disturbance on biogeochemical fluxes in tropical seascapes.

Tropical seascapes rely on the feedback relationships among mangrove forests, seagrass meadows, and coral reefs, as they mutually facilitate and enhance each other's functionality. Biogeochemical fluxes link tropical coastal habitats by exchanging material flows and energy through various natural processes that determine the conditions for life and ecosystem functioning. However, little is known about the seascape-scale implications of anthropogenic disruptions to these linkages. Despite the limited number of integrated empirical studies available (with only 11 out of 81 selected studies focusing on the integrated dynamics of mangroves, seagrass, and corals), this review emphasizes the importance of biogeochemical fluxes for ecosystem connectivity in tropical seascapes. It identifies four primary anthropogenic influences that can disturb these fluxes-nutrient enrichment, chemical pollution, microbial pollution, and solid waste accumulation-resulting in eutrophication, increased disease incidence, toxicity, and disruptions to water carbonate chemistry. This review also highlights significant knowledge gaps in our understanding of biogeochemical fluxes and ecosystem responses to perturbations in tropical seascapes. Addressing these knowledge gaps is crucial for developing practical strategies to conserve and manage connected seascapes effectively. Integrated research is needed to shed light on the complex interactions and feedback mechanisms within these ecosystems, providing valuable insights for conservation and management practices.

Symbiodiniaceae diversity varies by host and environment across thermally distinct reefs.

Endosymbiotic dinoflagellates (Symbiodiniaceae) influence coral thermal tolerance at both local and regional scales. In isolation, the effects of host genetics, environment, and thermal disturbances on symbiont communities are well understood, yet their combined effects remain poorly resolved. Here, we investigate Symbiodiniaceae across 1300 km in Australia's Coral Sea Marine Park to disentangle these interactive effects. We identified Symbiodiniaceae to species-level resolution for three coral species (Acropora cf humilis, Pocillopora verrucosa, and Pocillopora meandrina) by sequencing two genetic markers of the symbiont (ITS2 and psbAncr), paired with genotype-by-sequencing of the coral host (DArT-seq). Our samples predominantly returned sequences from the genus Cladocopium, where Acropora cf humilis affiliated with C3k, Pocillopora verrucosa with C. pacificum, and Pocillopora meandrina with C. latusorum. Multivariate analyses revealed that Acropora symbionts were driven strongly by local environment and thermal disturbances. In contrast, Pocillopora symbiont communities were both partitioned 2.5-fold more by host genetic structure than by environmental structure. Among the two Pocillopora species, the effects of environment and host genetics explained four times more variation in symbionts for P. meandrina than P. verrucosa. The concurrent bleaching event in 2020 had variable impacts on symbiont communities, consistent with patterns in P. verrucosa and A. cf humilis, but not P. meandrina. Our findings demonstrate how symbiont macroscale community structure responses to environmental gradients depend on host species and their respective population structure. Integrating host, symbiont, and environmental data will help forecast the adaptive potential of corals and their symbionts amidst a rapidly changing environment.

Poleward migration of tropical corals inhibited by future trends of seawater temperature and calcium carbonate (CaCO3) saturation.

Poleward range expansion of marine organisms is commonly attributed to anthropogenic ocean warming. However, the extent to which a single species can migrate poleward remains unclear. In this study, we used molecular data to examine the current distribution of the Pocillopora damicornis species complex in Taiwan waters and applied niche modeling to predict its potential range through the end of the 21st Century. The P. damicornis species complex is widespread across shallow, tropical and subtropical waters of the Indo-Pacific regions. Our results revealed that populations from subtropical nonreefal coral communities are P. damicornis, whose native geographical ranges are approximately between 23°N and 35°N. In contrast, those from tropical reefs are P. acuta. Our analysis of 50 environmental data layers demonstrated that the concentrations of CaCO3 polymorphs had the greatest contributions to the distributions of the two species. Future projections under intermediate shared socioeconomic pathways (SSP) 2-4.5 and very high (SSP5-8.5) scenarios of greenhouse gas emissions showed that while sea surface temperature (SST) isotherms would shift northwards, saturation isolines of two CaCO3 polymorphs, calcite (Ωcal) and aragonite (Ωarag), would shift southwards by 2100. Subsequent predictions of future suitable habitats under those conditions indicated that distinct delimitation of geographical ranges for the two species would persist, and neither would extend beyond its native geographical zones, indicating that tropical Taiwan waters are the northern limit for P. acuta. In contrast, subtropical waters are the southern limit for P. damicornis. We concluded that the decline in CaCO3 saturation would make high latitudes less inhabitable, which could be one of the boundary elements that limit poleward range expansion driven by rising SSTs and preserve the latitudinal diversity gradient (LDG) on Earth. Consequently, poleward migration of tropical reef corals to cope with warming oceans should be reevaluated.

Corals survive severe bleaching event in refuges related to taxa, colony size, and water depth.

Marine heatwaves are increasing in frequency and duration, threatening tropical reef ecosystems through intensified coral bleaching events. We examined a strikingly variable spatial pattern of bleaching in Moorea, French Polynesia following a heatwave that lasted from November 2018 to July 2019. In July 2019, four months after the onset of bleaching, we surveyed > 5000 individual colonies of the two dominant coral genera, Pocillopora and Acropora, at 10 m and 17 m water depths, at six forereef sites around the island where temperature was measured. We found severe bleaching increased with colony size for both coral genera, but Acropora bleached more severely than Pocillopora overall. Acropora bleached more at 10 m than 17 m, likely due to higher light availability at 10 m compared to 17 m, or greater daily temperature fluctuation at depth. Bleaching in Pocillopora corals did not differ with depth but instead varied with the interaction of colony size and Accumulated Heat Stress (AHS), in that larger colonies (> 30 cm) were more sensitive to AHS than mid-size (10-29 cm) or small colonies (5-9 cm). Our findings provide insight into complex interactions among coral taxa, colony size, and water depth that produce high spatial variation in bleaching and related coral mortality.

Sequential Treatment Application Robot (STAR) for high-replication marine experimentation.

Marine organisms are often subject to numerous anthropogenic stressors, resulting in widespread ecosystem degradation. Physiological responses to these stressors, however, are complicated by high biological variability, species-specific sensitivities, nonlinear relationships, and countless permutations of stressor combinations. Nevertheless, quantification of these relationships is paramount for parameterizing predictive tools and ultimately for effective management of marine resources. Multi-level, multi-stressor experimentation is therefore key, yet the high replication required has remained a logistical challenge and a financial barrier. To overcome these issues, we created an automated system for experimentation on marine organisms, the Sequential Treatment Application Robot (STAR). The system consists of a track-mounted robotic arm that sequentially applies precision treatments to independent aquaria via syringe and peristaltic pumps. The accuracy and precision were validated with dye and spectrophotometry, and stability was demonstrated by maintaining corals under treatment conditions for more than a month. The system is open source and scalable in that additional treatments and replicates may be added without incurring multiplicative costs. While STAR was designed for investigating the combined impacts of nutrients, warming, and disease on reef-building corals, it is highly customizable and may be used for experimentation involving a diverse array of treatments and species.

Metabolic signatures of two scleractinian corals from the northern South China sea in response to extreme high temperature events.

Coral bleaching events are becoming increasingly common worldwide, causing widespread coral mortality. However, not all colonies within the same coral taxa show sensitivity to bleaching events, and the current understanding of the metabolic mechanisms underlying thermal bleaching in corals remains limited. We used untargeted metabolomics to analyze the biochemical processes involved in the survival of two bleaching phenotypes of the common corals Pavona decussata and Acropora pruinosa, during a severe bleaching event in the northern South China Sea in 2020. During thermal bleaching, P. decussata and A. pruinosa significantly accumulated energy products such as succinate and EPA, antioxidants and inflammatory markers, and reduced energy storage substances like glutamate and thymidine. KEGG analysis revealed enrichment of energy production pathways such as ABC transporters, nucleotide metabolism and lipid metabolism, suggesting the occurrence of oxidative stress and energy metabolism disorders in bleached corals. Notably, heat stress exerted distinct effects on metabolic pathways in the two coral species, e.g., P. decussata activating carbohydrate metabolism pathways like glycolysis and the TCA cycle, along with amino acid metabolism pathways, whereas A. pruinosa significantly altered the content of multiple small peptides affected amino acid metabolism. Furthermore, the osmoregulatory potential of corals correlates with their ability to survive in heat-stress environments in the wild. This study provides valuable insights into the metabolic mechanisms linked to thermal tolerance in reef-building corals, contributes to the understanding of corals' adaptive potential to heat stress induced by global warming and lays the foundation for developing targeted conservation strategies in the future.

Gene expression profiles of Japanese precious coral Corallium japonicum during gametogenesis.

Background: Corallium japonicum, a prized resource in Japan, plays a vital role in traditional arts and fishing industries. Because of diminished stock due to overexploitation, ongoing efforts are focused on restoration through transplantation. This study aimed to enhance our understanding of the reproductive biology of these valuable corals and find more efficient methods for sex determination, which may significantly contribute to conservation initiatives. Methods: We used 12 three-month aquarium reared C. japonicum colony fragments, conducted histological analysis for maturity and sex verification, and performed transcriptome analysis via de novo assembly and mapping using the C. rubrum transcriptome to explore gene expression differences between female and male C. japonicum. Results: Our histological observations enabled sex identification in 33% of incompletely mature samples. However, the sex of the remaining 67% of samples, classified as immature, could not be identified. RNA-seq yielded approximately 21-31 million short reads from 12 samples. De novo assembly yielded 404,439 highly expressed transcripts. Among them, 855 showed significant differential expression, with 786 differentially expressed transcripts between females and males. Heatmap analysis highlighted 283 female-specific and 525 male-specific upregulated transcripts. Transcriptome assembly mapped to C. rubrum yielded 28,092 contigs, leading to the identification of 190 highly differentially expressed genes, with 113 upregulated exclusively in females and 70 upregulated exclusively in males. Blastp analysis provided putative protein annotations for 83 female and 72 male transcripts. Annotation analysis revealed that female biological processes were related to oocyte proliferation and reproduction, whereas those in males were associated with cell adhesion. Discussion: Transcriptome analysis revealed sex-specific gene upregulation in incompletely mature C. japonicum and shared transcripts with C. rubrum, providing insight into its gene expression patterns. This study highlights the importance of using both de novo and reference-based assembly methods. Functional enrichment analysis showed that females exhibited enrichment in cell proliferation and reproduction pathways, while males exhibited enrichment in cell adhesion pathways. To the best of our knowledge, this is the first report on the gene expressions of each sex during the spawning season. Our findings offer valuable insights into the physiological ecology of incompletely mature red Japanese precious corals and suggest a method for identifying sex using various genes expressed in female and male individuals. In the future, techniques such as transplantation, artificial fertilization, and larval rearing may involve sex determination methods based on differences in gene expression to help conserve precious coral resources and ecosystems.

The coefficient of conformism of a correlative prediction (CCCP): Building up reliable nano-QSPRs/QSARs for endpoints of nanoparticles in different experimental conditions encoded via quasi-SMILES.

Simulation of the physicochemical and biochemical behavior of nanomaterials has its own specifics. However, the main goal of modeling for both traditional substances and nanomaterials is the same. This is an ecologic risk assessment. The universal indicator of toxicity is the n-octanol/water partition coefficient. Mutagenicity indicates the possibility of future undesirable environmental effects, possibly greater than toxicity. Models have been proposed for the octanol/water distribution coefficient of gold nanoparticles and the mutagenicity of silver nanoparticles. Unlike the previous studies, here the models are built using an updated scheme, which includes two improvements. Firstly, the computing involves a new criterion for prediction potential, the so-called coefficient of conformism of a correlative prediction (CCCP); secondly, the Las Vegas algorithm is used to select the potentially most promising models from a group of models obtained by the Monte Carlo algorithm. Apparently, CCCP is a measure of the predictive potential (not only correlation). This can give an advantage in developing a model in comparison to using the classic determination coefficient. Likely, CCCP can be more informative than the classical determination coefficient. The Las Vegas algorithm is able to improve the model obtained by the Monte Carlo method.

Gene expression plasticity facilitates acclimatization of a long-lived Caribbean coral across divergent reef environments.

Local adaptation can increase fitness under stable environmental conditions. However, in rapidly changing environments, compensatory mechanisms enabled through plasticity may better promote fitness. Climate change is causing devastating impacts on coral reefs globally and understanding the potential for adaptive and plastic responses is critical for reef management. We conducted a four-year, three-way reciprocal transplant of the Caribbean coral Siderastrea siderea across forereef, backreef, and nearshore populations in Belize to investigate the potential for environmental specialization versus plasticity in this species. Corals maintained high survival within forereef and backreef environments, but transplantation to nearshore environments resulted in high mortality, suggesting that nearshore environments present strong environmental selection. Only forereef-sourced corals demonstrated evidence of environmental specialization, exhibiting the highest growth in the forereef. Gene expression profiling 3.5 years post-transplantation revealed that transplanted coral hosts exhibited profiles more similar to other corals in the same reef environment, regardless of their source location, suggesting that transcriptome plasticity facilitates acclimatization to environmental change in S. siderea. In contrast, algal symbiont (Cladocopium goreaui) gene expression showcased functional variation between source locations that was maintained post-transplantation. Our findings suggest limited acclimatory capacity of some S. siderea populations under strong environmental selection and highlight the potential limits of coral physiological plasticity in reef restoration.

Comparison of physiological and transcriptome responses of corals to strong light and high temperature.

Coral reefs are essential for marine ecology and biodiversity. Global climate change has resulted in severe coral reef degradation, partly via coral bleaching, which is caused by rising sea temperatures and solar light intensity. In this study, we examined the impact of strong light (300 µmol.m-2.s-1) and high temperature (33°C) on the growth, immunity, and gene expression of Galaxea fascicularis. Strong light caused coral bleaching in the absence of high sea temperatures, while no obvious bleaching was observed under high temperature alone. The effect of strong light on calcification rate of G. fascicularis is significantly weaker than that of high temperature. Both strong light and high temperatures significantly affected the immune enzyme activity of G. fascicularis symbionts, with the former having a strong effect on their photosystem. Temperature affected the digestive system, replication and repair, and cell growth and death of coral hosts, as indicated by transcriptomics analysis. These results provide a valuable for strategies to mitigate coral bleaching. TEASER: We explored the effects of strong light exposure and high temperature on coral reefs and their symbiont algae.

Decadal demographic shifts and size-dependent disturbance responses of corals in a subtropical warming hotspot.

Long-term demographic studies at biogeographic transition zones can elucidate how body size mediates disturbance responses. Focusing on subtropical reefs in eastern Australia, we examine trends in the size-structure of corals with contrasting life-histories and zoogeographies surrounding the 2016 coral bleaching event (2010-2019) to determine their resilience and recovery capacity. We document demographic shifts, with disproportionate declines in the number of small corals and long-term persistence of larger corals. The incidence of bleaching (Pocillopora, Turbinaria) and partial mortality (Acropora, Pocillopora) increased with coral size, and bleached corals had greater risk of partial mortality. While endemic Pocillopora experienced marked declines, decadal stability of Turbinaria despite bleaching, coupled with abundance increase and bleaching resistance in Acropora indicate remarkable resilience of these taxa in the subtropics. Declines in the number of small corals and variable associations with environmental drivers indicate bottlenecks to recovery mediated by inhibitory effects of thermal extremes for Pocillopora (heat stress) and Acropora (heat and cold stress), and stimulatory effects of chlorophyll-a for Turbinaria. Although our study reveals signs of resilience, it foreshadows the vulnerability of subtropical corals to changing disturbance regimes that include marine heatwaves. Disparity in population dynamics suggest that subtropical reefs are ecologically distinct from tropical coral reefs.