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Microbes perform critical functions in corals, yet most knowledge is derived from the photic zone. Here, we discover two mollicutes that dominate the microbiome of the deep-sea octocoral, Callogorgia delta, and likely reside in the mesoglea. These symbionts are abundant across the host's range, absent in the water, and appear to be rare in sediments. Unlike other mollicutes, they lack all known fermentative capabilities, including glycolysis, and can only generate energy from arginine provided by the coral host. Their genomes feature several mechanisms to interact with foreign DNA, including extensive CRISPR arrays and restriction-modification systems, which may indicate their role in symbiosis. We propose the novel family Oceanoplasmataceae which includes these symbionts and others associated with five marine invertebrate phyla. Its exceptionally broad host range suggests that the diversity of this enigmatic family remains largely undiscovered. Oceanoplasmataceae genomes are the most highly reduced among mollicutes, providing new insight into their reductive evolution and the roles of coral symbionts. Corals and other marine invertebrates host diverse microbes that remain poorly characterized, especially in the deep sea. Here the authors discover a new clade of bacteria with uniquely streamlined genomes in the tissue of a deep-sea coral that provide insights into the genome reduction of symbionts. [ABSTRACT FROM AUTHOR]

Over 30 herbicides have been detected in catchments and waters of the Great Barrier Reef (GBR) and their toxicity to key tropical species, including the coral endosymbiotic algae Symbiodiniaceae, is not generally considered in current water quality guideline values (WQGVs). Mutualistic symbionts of the family Symbiodiniaceae are essential for the survival of scleractinian corals. We tested the effects of nine GBR-relevant herbicides on photosynthetic efficiency (ΔF/Fm′) and specific growth rate (SGR) over 14 days of cultured coral endosymbiont Cladocopium goreaui (formerly Symbiodinium clade C1). All seven Photosystem II (PSII) herbicides tested inhibited ΔF/Fm′ and SGR, with toxicity thresholds for SGR ranging between 2.75 and 320 µg L−1 (no effect concentration) and 2.54–257 µg L−1 (EC10). There was a strong correlation between EC50s for ΔF/Fm′ and SGR for all PSII herbicides indicating that inhibition of ΔF/Fm′ can be considered a biologically relevant toxicity endpoint for PSII herbicides to this species. The non-PSII herbicides haloxyfop and imazapic did not affect ΔF/Fm′ or SGR at the highest concentrations tested. The inclusion of this toxicity data for Symbiodiniaceae will contribute to improving WQGVs to adequately inform risk assessments and the management of herbicides in tropical marine ecosystems. [ABSTRACT FROM AUTHOR]

Photosynthesis in cyanobacteria, green algae, and basal land plants is protected against excess reducing pressure on the photosynthetic chain by flavodiiron proteins (FLV) that dissipate photosynthetic electrons by reducing O2. In these organisms, the genes encoding FLV are always conserved in the form of a pair of two-type isozymes (FLVA and FLVB) that are believed to function in O2 photo-reduction as a heterodimer. While coral symbionts (dinoflagellates of the family Symbiodiniaceae) are the only algae to harbor FLV in photosynthetic red plastid lineage, only one gene is found in transcriptomes and its role and activity remain unknown. Here, we characterized the FLV genes in Symbiodiniaceae and found that its coding region is composed of tandemly repeated FLV sequences. By measuring the O2-dependent electron flow and P700 oxidation, we suggest that this atypical FLV is active in vivo. Based on the amino-acid sequence alignment and the phylogenetic analysis, we conclude that in coral symbionts, the gene pair for FLVA and FLVB have been fused to construct one coding region for a hybrid enzyme, which presumably occurred when or after both genes were inherited from basal green algae to the dinoflagellate. Immunodetection suggested the FLV polypeptide to be cleaved by a post-translational mechanism, adding it to the rare cases of polycistronic genes in eukaryotes. Our results demonstrate that FLV are active in coral symbionts with genomic arrangement that is unique to these species. The implication of these unique features on their symbiotic living environment is discussed. [ABSTRACT FROM AUTHOR]

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Climate change-induced global warming threatens the survival of key ecosystems including shallow water coral reefs. Elevated temperatures can disrupt the normal physiological functioning of photosynthetic organisms by altering the fluidity and permeability of chloroplast membranes that is defined and regulated by their lipid composition. Since the habitat-forming reef corals rely on the obligatory symbiosis with dinoflagellates of the family Symbiodiniaceae, their heat stress response can be expected to be strongly influenced by the symbiont's lipid metabolism. However, in contrast to the steady increase in the knowledge of the functioning of coral symbionts at the genomic and transcriptomic level, the understanding of their membrane lipid composition and regulation in response to temperature stress is lagging behind. We have utilised mass spectrometry-based lipidomic analyses to identify the key polar lipids that form the biological membranes of reef coral symbionts, comparing the thermotolerant species Durusdinium trenchii with the thermosensitive taxon Cladocopium C3, both hosted by Acropora valida. Our results indicate that the superior thermotolerance D. trenchii inside the host corals could be achieved through (1) the amount and saturation of sulfoquinovosyldiacylglycerols, in particular through putative photosystem II interactions, (2) the increased digalactosyldiacylglycerol to monogalactosyldiacylglycerol ratio with the potential to stabilise thylakoid membranes and integrated proteins, and (3) the chaperone-like function of lyso-lipids. Thereby, our study provides novel insights into the heat tolerance of coral symbionts, contributing to the understanding of the potential of coral reef ecosystems to respond and adjust to heat stress events that are becoming more frequent due to climate change. Finally, our identification of multiple mechanisms of heat tolerance in Symbiodiniaceae furthers the knowledge of the general stress physiology of photosynthetic organisms. [ABSTRACT FROM AUTHOR]

Background: Large-scale coral bleaching events have become increasingly frequent in recent years. This process occurs when corals are exposed to high temperatures and intense light stress, leading to an overproduction of reactive oxygen species (ROS) by their endosymbiotic dinoflagellates. The ROS buildup prompts corals to expel these symbiotic microalgae, resulting in the corals' discoloration. Reducing ROS production and enhancing detoxification processes in these microalgae are crucial to prevent the collapse of coral reef ecosystems. However, research into the cell physiology and genetics of coral symbiotic dinoflagellates has been hindered by challenges associated with cloning these microalgae. Results: A procedure for cloning coral symbiotic dinoflagellates was developed in this study. Several species of coral symbionts were successfully cloned, with two of them further characterized. Experiments with the two species isolated from Turbinaria sp. showed that damage from light intensity at 340 μmol photons/m2/s was more severe than from high temperature at 36 °C. Additionally, preincubation in high salinity conditions activated their endogenous tolerance to bleaching stress. Pretreatment at 50 ppt salinity reduced the percentage of cells stained for ROS by 59% and 64% in the two species under bleaching stress compared to those incubated at 30 ppt. Furthermore, their Fv'/Fm' during the recovery period showed a significant improvement compared to the controls. Conclusions: These findings suggest that intense light plays a more important role than high temperatures in coral bleaching by enhancing ROS generation in the symbiotic dinoflagellates. The findings also suggest the genomes of coral symbiotic dinoflagellates have undergone evolutionary processes to develop mechanisms, regulated by gene expression, to mitigate damages caused by high temperature and high light stress. Understanding this gene expression regulation could contribute to strengthening corals' resilience against the impact of global climate change. [ABSTRACT FROM AUTHOR]

Several groups of tube-dwelling coral symbionts induce the formation of long, finger-like branches (“fingers”) on Montipora corals in the lagoons of Moorea, French Polynesia. We surveyed the prevalence and taxonomic diversity of these symbionts across the northern lagoons of Moorea, and documented the length and density of the finger structures on coral colonies. We found that the symbionts, which include gammarid amphipods and chaetopterid polychaete worms that were not previously known to associate with scleractinian corals, dramatically alter coral skeletal morphology, and may alter coral biology and reef ecology. [ABSTRACT FROM AUTHOR]

Genotypic characterization of Symbiodinium symbionts in hard corals has routinely involved coring, or the removal of branches or a piece of the coral colony. These methods can potentially underestimate the complexity of the Symbiodinium community structure and may produce lesions. This study demonstrates that microscale sampling of individual coral polyps provided suYcient DNA for identifying zooxanthellae clades by RFLP analyses, and subclades through the use of PCR amplification of the ITS-2 region of rDNA and denaturing-gradient gel electrophoresis. Using this technique it was possible to detect distinct ITS-2 types of Symbiodinium from two or three adjacent coral polyps. These methods can be used to intensely sample coral-symbiont population/communities while causing minimal damage. The effectiveness and fine scale capabilities of these methods were demonstrated by sampling and identifying phylotypes of Symbiodinium clades A, B, and C that co-reside within a single Montastraea faveolata colony. [ABSTRACT FROM AUTHOR]

Many corals bleach as a result of increased seawater temperature, which causes them to lose their vital symbiotic algae (Symbiodinium spp.) - unless these symbioses are able to adapt to global warming, bleaching threatens coral reefs worldwide. Here I show that some corals have adapted to higher temperatures, at least in part, by hosting specifically adapted Symbiodinium. If other coral species can host these or similar Symbiodinium taxa, they might adapt to warmer habitats relatively easily. [ABSTRACT FROM AUTHOR]

Coral symbionts are important members of the coral holobiont, and coral bacterial flora are essential in host health maintenance and coral conservation. Coral symbionts are affected by various environmental factors, such as seawater temperature, pH, and salinity. Although physicochemical and chemical factors have been highlighted as possible causes of these effects, the effects of water flow and the co-culture of different species corals have not been elucidated. In this study, we designed an artificial rearing environment to examine the impact of environmental and biological factors on Acropora tenuis, one of the major coral species in Okinawa, and Montipora digitata, during their co-culture. We intervened with the water flow to reveal that the movement of the rearing environment alters the bacterial flora of A. tenuis. During the rearing under captive environment, the alpha diversity of the coral microbiota increased, suggesting the establishment of rare bacteria from the ocean. No differences in the bacterial composition between the control and water flow groups were observed under the rearing conditions. However, the structure of the bacterial flora was significantly different in the co-culture group. Comparison of bacterial community succession strongly suggested that the differences observed were due to the suppressed transmission of bacteria from the ocean in the co-culture group. These results enhance our understanding of interactions between corals and shed light on the importance of regional differences and bacterial composition of coral flora. [ABSTRACT FROM AUTHOR]

Global warming is causing the loss of coral symbionts and their bleaching. Researches of coral recovery are very important for the conservation of coral reefs. The lipidomic approach can provide detailed information about the processes that take place in the coral during bleaching and recovery. Using supercritical fluid chromatography coupled with mass spectrometry, the dynamics of the main classes of storage lipids, triacylglycerols (TG) and monoalkyldiacylglycerols (MADAG), during the recovery of the octocoral Sinularia heterospiculata after heat stress (32°C) was examined. It was shown that MADAG plays a key role in the energy balance of S. heterospiculata after heat stress. Under stress, the coral S. heterospiculata primarily consumed saturated MADAG molecular species. Changes in the profile of TG molecular species occurred only on day 16 of the experiment. Probably, the stressed octocoral S. heterospiculata changes its energy strategy during recovery; therefore, the qualitative composition of storage lipids is rearranged during the recovery period. [ABSTRACT FROM AUTHOR]

Coral reef fauna is imperiled by the loss of coral cover due to increased mass bleaching. However, few studies have focused on the immediate effects of bleaching on the closely coral-associated fauna. Here, we investigated the impact of a coral bleaching event due to abnormally cold waters in the Gulf of California on Pocillopora-associated fauna. We focused on the cryptobenthic reef fishes (CRFs) and crustacean coral symbionts that are likely the most sensitive to habitat degradation because of their poor mobility. We found that a moderate bleaching event (~ 50% of Pocillopora cover) did not affect the occurrence of crustaceans. In contrast, bleaching was significantly associated with a decrease in CRFs numbers, particularly for the non-gobiids, revealing a shift in assemblage composition. Our study highlights that the CRFs, essential for reef functioning, are very sensitive to early signs of habitat alteration. [ABSTRACT FROM AUTHOR]

Endogenous viral elements (EVEs) offer insight into the evolutionary histories and hosts of contemporary viruses. This study leveraged DNA metagenomics and genomics to detect and infer the host of a non-retroviral dinoflagellate-infecting +ssRNA virus (dinoRNAV) common in coral reefs. As part of the Tara Pacific Expedition, this study surveyed 269 newly sequenced cnidarians and their resident symbiotic dinoflagellates (Symbiodiniaceae), associated metabarcodes, and publicly available metagenomes, revealing 178 dinoRNAV EVEs, predominantly among hydrocoral-dinoflagellate metagenomes. Putative associations between Symbiodiniaceae and dinoRNAV EVEs were corroborated by the characterization of dinoRNAV-like sequences in 17 of 18 scaffold-scale and one chromosome-scale dinoflagellate genome assembly, flanked by characteristically cellular sequences and in proximity to retroelements, suggesting potential mechanisms of integration. EVEs were not detected in dinoflagellate-free (aposymbiotic) cnidarian genome assemblies, including stony corals, hydrocorals, jellyfish, or seawater. The pervasive nature of dinoRNAV EVEs within dinoflagellate genomes (especially Symbiodinium), as well as their inconsistent within-genome distribution and fragmented nature, suggest ancestral or recurrent integration of this virus with variable conservation. Broadly, these findings illustrate how +ssRNA viruses may obscure their genomes as members of nested symbioses, with implications for host evolution, exaptation, and immunity in the context of reef health and disease. A study part of the Tara Pacific Expedition that surveyed newly sequenced and publicly available metagenomes and genomes revealed pervasive non-retroviral dinoflagellate-infecting endogenous +ssRNA viral elements within coral symbionts. [ABSTRACT FROM AUTHOR]

Matthew Nitschke grows coral symbionts in a slowly warming tank to prepare reef life for climate change. [ABSTRACT FROM AUTHOR]

Scleractinian corals provide habitats for a broad variety of cryptofauna, which in turn may contribute to the overall functioning of coral symbiomes. Among these invertebrates, hydrozoans belonging to the genus Zanclea represent an increasingly known and ecologically important group of coral symbionts. In this study, we analysed 321 Zanclea colonies associated with 31 coral genera collected from 11 localities across the Indo-Pacific and Caribbean regions, and used a multi-disciplinary approach to shed light on the evolution and biogeography of the group. Overall, we found high genetic diversity of hydrozoans that spans nine clades corresponding to cryptic or pseudo-cryptic species. All but two clades are associated with one or two coral genera belonging to the Complex clade, whereas the remaining ones are generalists associated with both Complex and Robust corals. Despite the observed specificity patterns, no congruence between Zanclea and coral phylogenies was observed, suggesting a lack of coevolutionary events. Most Zanclea clades have a wide distribution across the Indo-Pacific, including a generalist group extending also into the Caribbean, while two host-specific clades are possibly found exclusively in the Red Sea, confirming the importance of this peripheral region as an endemicity hotspot. Ancestral state reconstruction suggests that the most recent common ancestor of all extant coral-associated Zanclea was a specialist species with a perisarc, occurring in what is now known as the Indo-Pacific. Ultimately, a mixture of geography- and host-related diversification processes is likely responsible for the observed enigmatic phylogenetic structure of coral-associated Zanclea. [ABSTRACT FROM AUTHOR]

This article presents a synthesis of information about the massive oil spill in Brazil (2019/2020). The event affected 11 states; however, the majority of the oil residue was collected (~ 5380 tons) near nine states (99.8%) in northeastern Brazil. This spill was not the largest in volume (between 5000 m3 and 12,000 m3) recorded in tropical oceans, but it was the most extensive (2890 km). This spill develops an overwashed tar that remains mostly in the undersurface drift (non-floating oil plume) below 17 m of depth while on the continental shelf. Ten ecosystems were impacted, with potentially more severe effects in mangroves and seagrasses. Certain negative effects are still understudied, such as effects on tropical reefs and rhodolith beds. A total of 57 protected areas in seven management categories were affected, most of which (60%) were characterized as multiple-use regions. The spill affected at least 34 threatened species, with impacts detected on plankton and benthic communities. Acute impacts were reported on echinoderms, coral symbionts, polychaetes, and sponges with evidence of oil ingestion. Socioeconomic impacts were detected in food security, public health, lodging, gender equality, tourism, and fishing, with reduced sales, prices, tourist attractiveness, gross domestic product, and employment. Moreover, chemical contamination was detected in some states by toxic metals (Hg, As, Cd, Pb, and Zn) and polycyclic aromatic hydrocarbons (acenaphthalene, fluoranthene, fluorene, naphthalene, and phenanthrene). This summary aims to aid in the design of science-based strategies to understand the impacts and develop strategies for the most extensive spill observed in tropical oceans. [ABSTRACT FROM AUTHOR]

Symbiosis between reef-building corals and unicellular algae (Symbiodiniaceae) fuels the growth and productivity of corals reefs. Capacity for Symbiodiniaceae to fix inorganic carbon (Ci) and translocate carbon compounds to the host is central to coral health, but how these processes change for corals thriving in environmental extremes remains largely unresolved. We investigate how a model coral—Pocillopora acuta—persists from a reef habitat into an adjacent extreme mangrove lagoon on the Great Barrier Reef. We combine respirometry and photophysiology measurements, Symbiodiniaceae genotyping, and 13C labelling to compare P. acuta metabolic performance across habitats, in relation to the Ci uptake and translocation capacity by symbionts' autotrophy. We show that differences in P. acuta metabolic strategies across habitats align with a shift in dominant host-associated Symbiodiniaceae taxon, from Cladocopium in the reef to Durusdinium in the mangroves. This shift corresponded with a change in "photosynthetic strategy", with P. acuta in the mangroves utilising absorbed light for photochemistry over non-photochemical quenching. Mangrove corals translocated similar proportions of carbon compared to the reefs, despite a lower Ci uptake. These trends indicate that coral survival in mangrove environments occurs through sustained translocation rate of organic compounds from coral symbionts to host. [ABSTRACT FROM AUTHOR]

A variety of symbionts inhabit colonies of scleractinian corals, the main component of coral reef ecosystems. Obligate symbionts spend almost their whole lives (except the pelagic larvae stage) on or in the host, while facultative symbionts are less tightly associated with the host and easily leave them when food becomes scarce and competition and predation increase. The influence of parasites on the life traits of obligate and facultative symbionts has not yet been studied. The first step in this direction is the study of basic parameters of parasite infracommunities associated with coral symbionts. It was suggested that obligate symbionts that are tightly associated with their hosts and their symbiotic communities are more often infected. An alternative hypothesis suggests that facultative symbionts are more frequently infected because they easily change habitats and consume a broad food spectrum. For several years, we studied parasites of obligate and facultative symbionts (fish, decapods crustaceans, mollusks) associated with the corals Acropora and Pocillopora in the Nha Trang Bay (South China Sea). The highest abundance and diversity of macroparasites (Monogenea, Cestoda, Trematoda, Nematoda, Copepoda) were found in facultative symbionts of corals, fish-parabionts. Obligate fish-inbionts were infected much less often (Cestoda, Trematoda, Nematoda). Obligate symbionts predominated in the invertebrate symbionts, which were also weakly infected. The low abundance and diversity of parasites in obligate symbionts suggest that there should be significant investments in antiparasitic defense, which, together with efficient antipredation defense, minimize the mortality of obligate symbionts. Their fecundity and population number are usually low. Facultative symbionts presumably suffer higher mortality than obligate symbionts, but a more intensive use of resources and higher population numbers may compensate for this. A significant increase in the infection rate with an increase in host body size is typical of facultative symbionts, which are less protected than obligate symbionts. The latter showed low infection levels in all size groups. The results suggest that the role of parasites in shaping the life strategies of symbionts is no less important than the role of predators. [ABSTRACT FROM AUTHOR]

Heat stress and other factors cause the loss of endosymbiotic dinoflagellates by corals, and is known as coral bleaching. Coral reef bleaching is a global environmental problem. To better understand corals' responses and adaptability to stressful conditions, we applied a lipidomic approach in combination with cytometry and microscopy to study the coral bleaching of Acropora aspera under heat stress (32 °C) and subsequent recovery. For eight days of bleaching, the coral lost 50% of its symbiont population and 100% after a week of recovery. It took 126 days to fully recover the symbiont population, content of chlorophyll a and reserve lipids. There were degradations in symbionts' thylakoids and disruption of thylakoid lipid homeostasis. Variations in the content of phosphatidylinositols involved in apoptosis and autophagy and changes in the molecular profile of glycosylceramides that may be involved in the sphingosine rheostat were observed. However, upon A. aspera bleaching, the loss of symbionts was compensated by increased mucociliary nutrition. An increase in the content of hydroxylated ceramideaminoethylphosphonates for membrane stabilization and a decrease in ether phosphatidylethanolamines for providing protection from oxidative stress may have been used as adaptation mechanisms by the coral host. Thus, the coral undergoes physiological and biochemical changes during heat stress that are aimed at mitigating the adverse destructive effects, which may be key to successful recovery. [ABSTRACT FROM AUTHOR]

The marine microbiome arouses an increasing interest, aimed at better understanding coral reef biodiversity, coral resilience, and identifying bioindicators of ecosystem health. The present study is a microbiome mining of three environmentally contrasted sites along the Hermitage fringing reef of La Réunion Island (Western Indian Ocean). This mining aims to identify bioindicators of reef health to assist managers in preserving the fringing reefs of La Réunion. The watersheds of the fringing reefs are small, steeply sloped, and are impacted by human activities with significant land use changes and hydrological modifications along the coast and up to mid-altitudes. Sediment, seawater, and coral rubble were sampled in austral summer and winter at each site. For each compartment, bacterial, fungal, microalgal, and protist communities were characterized by high throughput DNA sequencing methodology. Results show that the reef microbiome composition varied greatly with seasons and reef compartments, but variations were different among targeted markers. No significant variation among sites was observed. Relevant bioindicators were highlighted per taxonomic groups such as the Firmicutes:Bacteroidota ratio (8.4%:7.0%), the genera Vibrio (25.2%) and Photobacterium (12.5%) dominating bacteria; the Ascomycota:Basidiomycota ratio (63.1%:36.1%), the genera Aspergillus (40.9%) and Cladosporium (16.2%) dominating fungi; the genus Ostreobium (81.5%) in Chlorophyta taxon for microalgae; and the groups of Dinoflagellata (63.3%) and Diatomea (22.6%) within the protista comprising two dominant genera: Symbiodinium (41.7%) and Pelagodinium (27.8%). This study highlights that the identified bioindicators, mainly in seawater and sediment reef compartments, could be targeted by reef conservation stakeholders to better monitor La Réunion Island's reef state of health and to improve management plans. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) filters and preservatives, which are common constituents of sunscreens and other cosmetics, are reported as a threat for coastal coral reef ecosystems; however, few studies have assessed the effects of these compounds on coral health. This study presents the chronic effects (of measured, long-term and low concentrations) of some preservatives (ethylparaben, butylparaben), mineral UV filter (zinc oxide, ZnO) and organic UV filters (terephthalylidene dicamphor sulfonic acid, drometrizole trisiloxane, ethylhexyltriazone, butylmethoxydibenzoylmethane and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) on the maximal photosynthetic efficiency (Fv/Fm) of the symbionts associated with the scleractinian coral Stylophora pistillata. It first shows that for many organic filters, measured concentrations were significantly lower than nominal concentrations, due to the lipophilic nature of the compounds. In addition, the Fv/Fm was more sensitive to ZnO than all other sunscreen ingredients, with exposure to 90 µg L−1 ZnO for 35 d, reducing Fv/Fm by 38% compared with controls. The other UV filters tested showed no adverse effect on coral symbionts or animal tissue up to the concentration corresponding to their water solubility limit (and even above). Similarly, no adverse effect was observed in our conditions with the preservative ethylparaben, but the preservative butylparaben decreased the Fv/Fm by 25% at the highest concentration of 100 µg L−1. None of the sunscreen ingredients were as toxic to corals as the reference pollutants tributyltin, diuron and monuron, which significantly inhibited Fv/Fm at 10, 1 and 0.1 µg L−1, respectively. Overall, this study highlights the need to improve our knowledge on the in situ concentrations of UV filters and preservatives as well as their individual and combined effects on corals. [ABSTRACT FROM AUTHOR]

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

This research aimed to examine the interplay among carotenoids, total polyphenols, and indole alkaloids for the discovery of new bioactive compounds using "simplex-centroid" designs and response surface methodology (RSM). The antioxidant (AOA) and anti-inflammatory (AIA) activities of mixtures containing different proportions of each compound were evaluated by measuring the percentage inhibition of oxidation and spontaneous inflammation. The results showed that the highest AOAs were obtained with different mixtures of polyphenols, indole alkaloids, and carotenoids. The DPPH test revealed that a mixture of 16.94% polyphenols and 83.05% indole alkaloids produced the best results, whereas, for the ABTS test, 100% polyphenols gave the best results. The FRAP assay showed that the best-performing mixture was composed of 85.96% carotenoids and 14.03% polyphenols, with an IC50 of 8.85 ± 1.17 μg/mL. In contrast, the most potent AIA was obtained with 100% carotenoids. Model validation tests were performed and showed that the experimentally observed values for AOA and AIA were not significantly different from the values estimated by the fitted models. The results also showed that the RSM model can be used to estimate the behavior of mixed compounds in the development of new functional ingredients or the discovery of new bioactive compounds with pharmacological properties. Finally, the results also suggested that there is a good correlation between several AOA and AIA assays, which makes natural substances combining these biological activities particularly interesting. [ABSTRACT FROM AUTHOR]

Coral reefs rely heavily on reef fish for their health, yet overfishing has resulted in their decline, leading to an increase in fast-growing algae and changes in reef ecosystems, a phenomenon described as the phase-shift. A clearer understanding of the intricate interplay between herbivorous, their food, and their gut microbiomes could enhance reef health. This study examines the gut microbiome and isotopic markers (δ13C and δ15N) of four key nominally herbivorous reef fish species (Acanthurus chirurgus, Kyphosus sp., Scarus trispinosus, and Sparisoma axillare) in the Southwestern Atlantic's Abrolhos Reef systems. Approximately 16.8 million 16S rRNA sequences were produced for the four fish species, with an average of 317,047 ± 57,007 per species. Bacteria such as Proteobacteria, Firmicutes, and Cyanobacteria were prevalent in their microbiomes. These fish show unique microbiomes that result from co-diversification, diet, and restricted movement. Coral-associated bacteria (Endozoicomonas, Rhizobia, and Ruegeria) were found in abundance in the gut contents of the parrotfish species Sc. trispinosus and Sp. axillare. These parrotfishes could aid coral health by disseminating such beneficial bacteria across the reef. Meanwhile, Kyphosus sp. predominantly had Pirellulaceae and Rhodobacteraceae. Four fish species had a diet composed of turf components (filamentous Cyanobacteria) and brown algae (Dictyopteris). They also had similar isotopic niches, suggesting they shared food sources. A significant difference was observed between the isotopic signature of fish muscular gut tissue and gut contents, pointing to the role that host genetics and gut microbes play in differentiating fish tissues. [ABSTRACT FROM AUTHOR]

Crustaceans are one of the most widespread and speciose groups of marine organisms, fulfilling multiple ecological roles in numerous ecosystems. On coral reefs, many crustacean species form associations with scleractinian corals. Although the Red Sea is considered a biodiversity hotspot, few studies examined the diversity of coral-associated crustacean communities to date. In this study, 460 decapod crustaceans were recovered from 67 coral colonies of the three branching genera Acropora, Pocillopora and Stylophora in the central Saudi Arabian Red Sea. Crabs and shrimps were morphologically identified to the lowest taxonomic level possible, and portions of the mitochondrial COI and 16S rRNA genes were amplified with the objective of assessing their diversity and phylogenetic relationships. Finally, patterns of co-occurrence were evaluated to investigate the presence of species-specific symbiotic epifauna on different host corals. Overall, we recovered four families, five genera, and nine species of Red Sea crabs, nested into 11 molecular clades, and two families, eight genera and 11 species of shrimps, grouped within 12 lineages. Crabs of the species Trapezia tigrina were found to be exclusively associated with Pocillopora corals, while Tetralia crabs and the shrimps Jocaste japonica and Harpilius lutescens only occurred on Acropora colonies, providing evidence that potential loss of host corals due to local and global impacts could lead to consequent shifts in the symbiotic communities on reefs and to the loss of certain associated taxa. This study represents an advancement towards the understanding and molecular characterization of coral-associated benthic communities in the Red Sea and lays the ground for further research assessing the patterns of biodiversity, evolution, and ecological preferences of these organisms in the area. [ABSTRACT FROM AUTHOR]

The symbiotic relationships between coral animal host and autotrophic dinoflagellates are based on the mutual exchange and tight control of nutritional inputs supporting successful growth. The corals Sinularia heterospiculata and Acropora aspera were cultivated using a flow-through circulation system supplying seawater during cold and warm seasons of the year, then sorted into host cells and symbionts and subjected to phylogenetic, morphological, and advanced lipid analyses. Here we show, that the lipidomes of the dinoflagellates Cladocopium C1/C3 and acroporide-specific Cladocopium hosted by the corals, are determined by lipidomic features of different thermosensitivity and unique betaine- and phospholipid molecular species. Phosphatidylserines and ceramiaminoethylphosphonates are not detected in the symbionts and predominantly localized on the inner leaflet of the S. heterospiculata host plasma membrane. The transmembrane distribution of phosphatidylethanolamines of S. heterospiculata host changes during different seasons of the year, possibly contributing to mutualistic nutritional exchange across this membrane complex to provide the host with a secure adaptive mechanism and ecological benefits.An advanced lipidomic study of corals Sinularia heterospiculata and Acropora aspera showed that plasma membrane of host cells has unique vectorial lipidomic features and compositionally distinct lipid profile from their endosymbiotic dinoflagellates. [ABSTRACT FROM AUTHOR]

Symbiotic dinoflagellates in the genus Symbiodiniaceae play vital roles in promoting resilience and increasing stress tolerance in their coral hosts. While much of the world's coral succumb to the stresses associated with increasingly severe and frequent thermal bleaching events, live coral cover in Papua New Guinea (PNG) remains some of the highest reported globally despite the historically warm waters surrounding the country. Yet, in spite of the high coral cover in PNG and the acknowledged roles Symbiodiniaceae play within their hosts, these communities have not been characterized in this global biodiversity hotspot. Using high-throughput sequencing of the ITS2 rDNA gene, we profiled the endosymbionts of four coral species, Diploastrea heliopora, Pachyseris speciosa, Pocillopora acuta, and Porites lutea, across six sites in PNG. Our findings reveal patterns of Cladocopium and Durusdinium dominance similar to other reefs in the Coral Triangle, albeit with much greater intra- and intergenomic variation. Host- and site-specific variations in Symbiodiniaceae type profiles were observed across collection sites, appearing to be driven by environmental conditions. Notably, the extensive intra- and intergenomic variation, coupled with many previously unreported sequences, highlight PNG as a potential hotspot of symbiont diversity. This work represents the first characterization of the coral-symbiont community structure in the PNG marine biodiversity hotspot, serving as a baseline for future studies. [ABSTRACT FROM AUTHOR]

The application of beneficial microorganisms for corals (BMC) decreases the bleaching susceptibility and mortality rate of corals. BMC selection is typically performed via molecular and biochemical assays, followed by genomic screening for BMC traits. Herein, we present a comprehensive in silico framework to explore a set of six putative BMC strains. We extracted high-quality DNA from coral samples collected from the Red Sea and performed PacBio sequencing. We identified BMC traits and mechanisms associated with each strain as well as proposed new traits and mechanisms, such as chemotaxis and the presence of phages and bioactive secondary metabolites. The presence of prophages in two of the six studied BMC strains suggests their possible distribution within beneficial bacteria. We also detected various secondary metabolites, such as terpenes, ectoines, lanthipeptides, and lasso peptides. These metabolites possess antimicrobial, antifungal, antiviral, anti-inflammatory, and antioxidant activities and play key roles in coral health by reducing the effects of heat stress, high salinity, reactive oxygen species, and radiation. Corals are currently facing unprecedented challenges, and our revised framework can help select more efficient BMC for use in studies on coral microbiome rehabilitation, coral resilience, and coral restoration. [ABSTRACT FROM AUTHOR]

Microbial diversity has been extensively explored in reef-building corals. However, the functional roles of coral-associated microorganisms remain poorly elucidated. Here, we recover 191 bacterial and 10 archaeal metagenome-assembled genomes (MAGs) from the coral Acropora kenti (formerly A. tenuis) and adjacent seawater, to identify microbial functions and metabolic interactions within the holobiont. We show that 82 MAGs were specific to the A. kenti holobiont, including members of the Pseudomonadota, Bacteroidota, and Desulfobacterota. A. kenti-specific MAGs displayed significant differences in their genomic features and functional potential relative to seawater-specific MAGs, with a higher prevalence of genes involved in host immune system evasion, nitrogen and carbon fixation, and synthesis of five essential B-vitamins. We find a diversity of A. kenti-specific MAGs encode the biosynthesis of essential amino acids, such as tryptophan, histidine, and lysine, which cannot be de novo synthesised by the host or Symbiodiniaceae. Across a water quality gradient spanning 2° of latitude, A. kenti microbial community composition is correlated to increased temperature and dissolved inorganic nitrogen, with corresponding enrichment in molecular chaperones, nitrate reductases, and a heat-shock protein. We reveal mechanisms of A. kenti-microbiome-symbiosis on the Great Barrier Reef, highlighting the interactions underpinning the health of this keystone holobiont. This study provides insights into the functional roles of microbial symbionts within the reef-building coral Acropora kenti. The findings reveal molecular mechanisms underpinning coral health and adaptation to local environmental stressors, which may support host resilience in the face of anthropogenic climate change and pollution. [ABSTRACT FROM AUTHOR]

The increasing threat of ocean warming has led to the more frequent endangerment of coral reefs, including the heat-tolerant Pavona decussata. To shed light on the molecular mechanisms involved in the response of coral to ocean warming, we investigated the gene expression profiles of P. decussata after natural thermal stress. Using PacBio Sequel II sequencing technology, we obtained relatively complete transcriptome data for P. decussata and then analyzed its gene expression quantitatively with Illumina RNA-seq technology. We acquired information on gene function, structure, and expression profile from coral host and zooxanthellae. Analysis of Illumina sequencing data revealed that unbleached coral host might rely on the active utilization of amino acids to maintain a stable living condition based on the tricarboxylic acid cycle under high temperature stress, and that zooxanthellae might benefit from ammonium produced by coral host. Moreover, the downregulation of unbleached coral host gene expression in innate immune pathways centered on the transcription factors that heat shock factor and nuclear factor (NF)-κB, as well as the tyrosine kinase pathway, might be crucial for maintaining the equilibrium of the zooxanthellae under thermal stress. Thus, the differences in these molecular mechanisms could determine, to some extent, whether coral host can maintain a symbiotic relationship with algae under heat stress. This study elucidated the molecular mechanisms underlying differences in thermal tolerance within P. decussata species and supported further theoretical basis in coral molecular biology and ecological conservation, which enhance our comprehension of coral responses to future climate change. [ABSTRACT FROM AUTHOR]

Variously shaped corals, such as branching and massive corals, exhibit divergent environmental susceptibility properties. The susceptibility potential of these corals may be regulated by specific symbiotic Symbiodiniaceae and bacteria. In this study, we investigated seawater characteristics between the north and south zones at the Wuzhizhou Island (WZZ), sampled branching coral Acropora hyacinthus, lamellar coral Montipora informis, and massive coral (Galaxea fascicularis and Porites lutea). Physiological characteristics were measured, and amplicon sequencing was performed to Symbiodiniaceae and bacterial community structure analysis. Corals experienced severe anthropogenic disturbance, with more than 1.4-fold increase in DIN, including NH 4 + , NO 3 - , and NO 2 - in the north of the WZZ Island compared to the southern region. However, massive corals (G. fascicularis and P. lutea) showed relatively less disruption in both their symbiont composition and physiological responses. Notably, M. informis displayed distinct variations, with disturbances in the northern region resulted in a decline in the density of symbiotic micro-algae associated with Cladocopium sp. C26 due to elevated concentrations of ammonium and nitrate. The four coral species hosted different symbionts within the same area. P. lutea hosted Cladocopium sp. C15 with the lowest density of symbiotic micro-algae, along with the lowest Fv/Fm and YII values compared to other corals in the southern zone. G. fascicularis exhibited high abundance of Durusdinium sp. D1 and D4, which showed strong correlation with Fv/Fm. In southern M. informis, Cladocopium sp. C26 was identified as the predominant symbiotic micro-algae that displayed a significant positive correlation with YII. The bacterial community composition and metabolism functional attribution predicted by PICRUSt differed between A. hyacinthus, M. informis, and massive corals (G. fascicularis, P. lutea). Comprehensive analysis revealed different susceptibility properties among branching, lamellar, and massive corals under anthropogenic disturbance associated with changes in Symbiodiniaceae and bacterial community. [ABSTRACT FROM AUTHOR]

Establishment of the coral–algal symbiosis begins during early ontogeny when juveniles acquire a mix of algae from their environment that often differs from the adults' algal assemblages. Despite the importance of the type of Symbiodiniaceae to this symbiosis, it is largely unknown how coral host identity and environment affect symbiosis establishment and is affected by the genetic composition of the symbionts. Here, we reciprocally transplanted planulae of the octocoral Rhytisma fulvum (Forskål, 1775) across depths and monitored the algal assemblages in the developing juveniles for 11 months. We then compared these to adult assemblages using ITS2 metabarcoding. Juveniles were consistently dominated by Symbiodinium, in addition to multiple Cladocopium species, which shifted in dominance with the juvenile age but maintained high similarity across depths. The type of Symbiodiniaceae environmentally available thus likely contributes to the algal symbionts that are initially acquired, while host identity may play a significant role in selecting for symbionts that are maintained during juvenile development. [ABSTRACT FROM AUTHOR]

Reef-building corals are a fundamental pillar of coral reef ecosystems in tropical and subtropical shallow environments. Corals harbor symbiotic dinoflagellates belonging to the family Symbiodiniaceae, commonly known as zooxanthellae. Extensive research has been conducted on this symbiotic relationship, yet the fundamental information about the distribution and localization of Symbiodiniaceae cells in corals is still limited. This information is crucial to understanding the mechanism underlying the metabolite exchange between corals and their algal symbionts, as well as the metabolic flow within holobionts. To examine the distribution of Symbiodiniaceae cells within corals, in this study, we used fluorescence imaging and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MS-Imaging) on branches of the Acropora tenuis coral. We successfully prepared frozen sections of the coral for molecular imaging without fixing or decalcifying the coral branches. By combining the results of MS-Imaging with that of the fluorescence imaging, we determined that the algal Symbiodiniaceae symbionts were not only localized in the tentacle and surface region of the coral branches but also inhabited the in inner parts. Therefore, the molecular imaging technique used in this study could be valuable to further investigate the molecular dynamics between corals and their symbionts. [ABSTRACT FROM AUTHOR]

Although apicomplexans are a widely recognized and important parasitic group, little is known about those associated with invertebrates, such as reef-building scleractinian corals. To resolve the potential impact of apicomplexans on coral health, it is first necessary to further describe this group of putative parasites and determine their prevalence among host species. Here, it was hypothesized that apicomplexan prevalence would vary seasonally, similar to what occurs in other marine apicomplexans as well as some coral symbionts. To test this, Caribbean scleractinian species Porites astreoides, Montastraea (= Orbicella) annularis, M. (= O.) faveolata, and Siderastrea siderea were sampled seasonally from two reefs each in the Florida Keys and the Bahamas for 9- and 5.5-year periods, respectively. Utilizing a PCR-based screening assay, apicomplexan DNA was detected from most Floridian (80.1 %: n = 555/693) and Bahamian (90.7 %: n = 311/343) coral tissue samples collected over these multi-year periods. Furthermore, apicomplexan DNA was detected from nearly all (98.7 %: n = 78/79) single polyps sampled at multiple locations within six M. faveolata colonies, indicating little to no intracolonial variation in the screening assay. Mixed-model logistic regression was utilized to determine the effects of season, host species, and reef on apicomplexan prevalence. The model identified a significant seasonal effect, with the highest apicomplexan prevalence occurring during fall. There also was a large effect of host species, with apicomplexan prevalence significantly lower among S. siderea colonies relative to the other species. While reef did not have a significant effect in the full model, there was a significant difference in apicomplexan prevalence between Floridian and Bahamian reefs for S. siderea, implying regional differences in this host species. Despite seasonal and species-specific differences in prevalence, apicomplexans are ubiquitous constituents of these particular scleractinian coral species from Florida and the Bahamas. [ABSTRACT FROM AUTHOR]

The solitary ascidian Styela plicata is an introduced species in harbors of temperate and tropical oceans around the world. The invasive potential of this species has been studied through reproductive biology and population genetics but no study has yet examined the microbial diversity associated with this ascidian and its potential role in host ecology and invasiveness. Here, we used 16S rRNA gene tag pyrosequencing and transmission electron microscopy to characterize the abundance, diversity and host-specificity of bacteria associated with 3 Mediterranean individuals of S. plicata. Microscopy revealed low bacterial abundance in the inner tunic and their absence from gonad tissues, while pyrosequencing revealed a high diversity of S. plicata-associated bacteria (284 OTUs from 16 microbial phyla) in the inner tunic. The core symbiont community was small and consisted of 16 OTUs present in all S. plicata hosts. This core community included a recently described ascidian symbiont ( Hasllibacter halocynthiae) and several known sponge and coral symbionts, including a strictly anaerobic Chloroflexi lineage. Most recovered bacterial OTUs (79.6 %) were present in single S. plicata individuals and statistical analyses of genetic diversity and community structure confirmed high variability of bacterial communities among host individuals. These results suggest that diverse and variable bacterial communities inhabit the tunic of S. plicata, including environmental and host-associated bacterial lineages that appear to be re-established each host generation. We hypothesize that bacterial communities in S. plicata are dynamic and have the potential to aid host acclimation to new habitats by establishing relationships with beneficial, locally sourced bacteria. [ABSTRACT FROM AUTHOR]

Using a novel molecular biomaker system (MBS), we assessed the physiological status of coral (Montastraea faveolata) challenged by heat stress by assaying specific cellular and molecular parameters. This technology is particularly relevant for corals because heat stress is thought to be an essential component of coral bleaching. This phenomenon is widely believed to be responsible for coral mortality worldwide, particularly during 1997-1998. Specific parameters of coral cellular physiology were assayed using the MBS that are indicative of a nonstressed or stressed condition. The MBS distinguished the separate and combined effects of heat and light on the 2 coral symbionts, a scleractinian coral and a dinoflagellate algae (zooxanthellae). This technology aids in the accurate diagnosis of coral condition because each parameter is physiologically well understood. Finally, the MBS technology is relatively inexpensive, easy to implement, and precise, and it can be quickly adapted to a high-throughout robotic system for mass sample analysis. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) have become an important concern among scientists and policymakers all around the globe. Despite this, the contribution of MPs to global warming and climate change, a significant aspect of the issue, has been overlooked. Continuous greenhouse gas (GHG) emissions resulting in climate change have long been a major issue with apparent consequences. Climate change and plastic crises are threatening our planet, and the co-occurrence of both would be catastrophic. This article addressed the links between microplastic pollution and climate change; how MPs contribute to climate change by interacting with water, air, and soil; and recommendations to address the issues together. Throughout their lives, plastics emit GHG. MPs in water impede the climate change mitigation potential of the ocean in different ways; they hamper photosynthesis and carbon sequestration by phytoplankton and the Blue Carbon Ecosystem. MPs induce GHG emissions from the soil. Airborne MPs have the potential to aid in cloud formation and interfere with atmospheric cooling. Climate change–induced extreme events redistribute MPs in the environment, causing the pollution to increase vertically and horizontally, which then aggravates the situation in a feedback loop. The evidence acquired in the study implies that MPs and climate change are inextricably linked and that MPs play a vital role in fueling climate change. This bridges the gap between MPs and climate change issues that were previously regarded separately. Due to the linkages between these intertwined challenges, integrated and holistic research and policy measures are required to address both crises concurrently. [ABSTRACT FROM AUTHOR]

The mitigation of coral bleaching requires adaptation of its endosymbionts to rising ocean temperatures, acidity, and ultra-violet radiation. While genetic transformation may offer a means for enhancing endosymbiont resilience to these environmental stressors, the opportunity for doing so in dinoflagellates is likely hampered, in part, by their armored cortex, which may present a formidable barrier to intracellular delivery. Here, using Breviolum minutum (Clade B Symbiodiniaceae) as a model, we show that this barrier may be moderated by first disrupting the outer plasma membrane with the detergent octyl β-D-glucopyranoside, followed by enzymatic digestion of the underlying cellulose with Cellulase RS and Macerozyme R-10. Treatment using this new protocol results in 61% reduction in calcofluor-based cell wall staining (i.e., 25% staining for protocol vs. 64% for control), thus demonstrating the ability for considerable cell wall digestion. Furthermore, protoplasts isolated thereby exhibit rapid cell wall recovery, as well as comparable PSII activity and cell growth as the control, thus suggesting that the protocol minimally affects acute- and long-term cellular function. Finally, the isolated protoplasts also show a potentially slight increase in permeability to a model exogenous cargo after electroporation with a non-optimized protocol. Collectively, this constitutes the first known successful generation of viable B. minutum protoplasts, and thus, serves as a foundation for future studies seeking to lower the barrier for transformation of these and possibly other Symbiodiniaceae. [ABSTRACT FROM AUTHOR]

Lipid molecular species profiles of marine invertebrates still remain very poorly understood. We have studied year-round variations in the levels of chlorophylls and reserve lipid molecular species such as triacylglycerols (TG), and monoalkyldiacylglycerol (MADAG) in octocoral Sinularia flexibilis and the hydrocoral Millepora platyphylla. Our results show that M. platyphylla and S. flexibilis display differences in the pattern of year-round variations in reserve lipids. Only in M. platyphylla, total reserve lipids correlated with seawater temperature, which may be associated with hydrocoral's predation on plankton. A decrease in total lipids leads to an increase in chlorophyll levels, which indicates transition to autotrophic nutrition mode. Differences between corals also may be associated with species of hosted symbiotic dinoflagellates that can be a source of fatty acids (FAs) for the biosynthesis of TG and MADAG by the coral host. This may be an explanation for the annual variations in TG molecular species with 22:6 PUFA in M. platyphylla, and TG molecular species with saturated, mono-, and dienoic FAs in S. flexibilis. Based on S. flexibilis as an example, we have shown that MADAGs are suggested to have several molecular pools, of which one may be related to the molecular profile of structural phospholipids with the same FAs. Year-round studies of lipidome can help understand the range and possible causes of seasonal biochemical variations in corals and may be useful for future analysis of trophic and symbiont–host interactions in cnidarians. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is defined as a property of individual genotypes to produce different phenotypes when exposed to different environmental conditions. This ability may be expressed at behavioral, biochemical, physiological, and/or developmental levels, exerting direct influence over species' demographic performance. In reef-building corals, a group critically threatened by global change in the Anthropocene, non-genetic mechanisms (i.e., epigenetic and microbiome variation) have been shown to participate in plastic physiological responses to environmental change. Yet, the precise way in which these mechanisms interact, contribute to such responses, and their adaptive potential is still obscure. The present work aims to fill this gap by using a multi-omics approach to elucidate the contribution and interconnection of the mechanisms modulating phenotypic plasticity in staghorn coral (Acropora cervicornis) clones subject to different depth conditions. Results show changes in lipidome, epigenome and transcriptome, but not in symbiotic and microbial communities. In addition, a potential shift toward a more heterotrophic feeding behavior was evidenced in corals at the deeper site. These observations are consistent with a multi-mechanism modulation of rapid acclimation in corals, underscoring the complexity of this process and the importance of a multifactorial approach to inform potential intervention to enhance coral adaptive capacity. [ABSTRACT FROM AUTHOR]

Coral reefs are globally important ecosystems with high species diversity at both the macro and micro scales. In recent years, coral reefs have been heavily impacted by anthropogenic and natural stressors, including emerging diseases. Many of these diseases have been identified in reef-building corals, but other invertebrate taxa, such as soft corals, are increasingly at risk. This study focuses on a hybrid species complex within soft corals of the genus Sinularia, which dominate the shallow reefs of Guam, and the broader Indo-Pacific. These soft corals exhibit varying levels of disease susceptibility to Sinularia tissue loss disease (STLD), a chronic wasting disease. In the current study, we used next-generation amplicon sequencing of prokaryotic and eukaryotic communities within these soft corals to characterize their microbiomes, and develop a better understanding of the etiology of STLD. There were differences in specific ASVs across the microbiomes of healthy colonies of Sinularia maxima, Sinularia polydactyla and their hybrid (S. maxima x S. polydactyla). There was also a decline in the relative abundance of putatively beneficial symbionts (Symbiodinaceae and Endozoicomonas) in STLD-affected soft corals, but no consistent shifts towards a specific microbial community associated with STLD. The soft coral microbiomes also contained a high relative abundance of ASVs typically associated with terrestrial runoff. Our results suggest that the STLD phenotype may be due to a combination of factors, including infection by a yet unknown etiologic agent, shifts in putatively beneficial symbionts, and anthropogenic impacts on this shallow nearshore reef. [ABSTRACT FROM AUTHOR]

Unlocking how coral endosymbionts (Symbiodiniaceae) regulate the susceptibility of corals to thermal stress-induced bleaching has been the focus of experimental heat stress studies on laboratory-maintained isolates for over 30 years. Multiple protocols to induce heat stress have been used, but the extent to which data can be reconciled across protocols remains unknown. We therefore first analysed past published heat stress studies on Symbiodiniaceae (Jan 1980–Jan 2023) to identify the range of protocols (ramping rate derived from time taken to reach the target heat stress temperatures from the initial ambient temperature, time retained under the target heat stress temperature, etc.) commonly used for experimentation. Temperature differences between ambient and maximum experimental temperatures spanned from 3 °C to 17 °C (mean = 6.8 °C), and only 41% of all studies reported a ramping rate, ranging from instantaneous to 0.02 °C/h (mean = 0.62 °C/h). Experiment length at the treatment temperature varied from < 24 h to > 2 months. We next experimentally quantified if the rate of heating impacted the observed physiological outcome for three Symbiodiniaceae taxa with differences in heat tolerance—Durusdinium trenchii, Breviolum psygmophilum and Breviolum minutum. Five experimental treatments were performed with different temperature ramping rates from 26 °C to 32 °C: 1 °C/1 h, 1 °C/12 h, 1 °C/1 d, 1 °C/2 d and 1 °C/3 d, spanning relatively acute to chronic. Changes in physiology were quantified daily as the maximum photochemical efficiency (Fv/Fm). Heating commonly induced decreases in Fv/Fm, and the change between the start and end of experiment (∆Fv/Fm) linearly increased with ramping rates. Our data suggests that slower ramping exacerbates thermal stress, though with varying magnitude across taxa as B. minutum, and D. trenchii proved less resilient than B. pysgmophilum. We discuss how these outcomes potentially impact the capacity to integrate biological responses observed from past experiments and highlights the need for more standardised experimental protocols. [ABSTRACT FROM AUTHOR]

Symbiotic invertebrates play crucial roles in coral reef ecosystems due to their extremely high abundance and biomass and by maintaining coral fitness and protecting them from predation. Among these invertebrates, symbiotic crabs of the family Trapeziidae are especially important for branching corals of the family Pocilloporidae. In this research, we studied the spatial arrangement and parameters of the populations of the symbiotic crab Trapezia septata at the early stage of Pocillopora verrucosa colony formation. This study was conducted based on symbionts sampled from small coral colonies exposed for three months at a coral nursery in Nha Trang Bay, Vietnam. As much as 59.5% of the study colonies are shown to be inhabited by the T. septata crab. The percentage of inhabited colonies grows proportionately to their volume. The male-to-female ratio is 1.4, being skewed to males. The number of males and females increases with the volume of inhabited colonies, as does the average size of individuals. Individual colonies are commonly inhabited by a single crab or heterosexual pairs. Sexual dimorphism was found, females being larger than males. A positive relationship between the sizes of males and females in pairs was revealed, as in 73% of pairs females were larger than males. The size of the clutch correlated positively to the size of the female. We hypothesize that the predominance of males in the population, as well as the individuals located among the hosts one by one, is the result of intersexual competition. [ABSTRACT FROM AUTHOR]

Global climate change is threatening the persistence of coral reefs as associated summer heatwaves trigger the loss of microalgal endosymbionts (Symbiodiniaceae) from the coral tissues, or coral bleaching. We infected aposymbiotic juveniles of the coral Acropora tenuis with either wildtype (WT10) or heat-evolved (SS1 or SS8) Symbiodiniaceae strains Cladocopium proliferum (formerly referred to as Cladocopium goreaui and Cladocopium C1acro). After 10 months at 27 °C, SS8-juveniles were 2 × larger than SS1- or WT10-juveniles. In response to a simulated heatwave (31 °C for 41 days), the WT10-juveniles bleached and showed a decline in respiration while cell densities and respiration in both SS-juvenile groups remained unchanged compared to the controls. These results reveal that some heat-evolved strains can increase the bleaching tolerance of juvenile corals without a trade-off against growth. This response is opposite to the lower nutrient provisioning often reported for naturally thermotolerant Symbiodiniaceae (e.g. genus Durusdinium), thereby offering enhanced fitness to the host without the ecological consequences of diminished growth. [ABSTRACT FROM AUTHOR]

Corals' endosymbiotic algae (Symbiodiniaceae) supply much of the energetic demands of the host, and some symbionts, such as Durusdinium spp., may confer higher thermal tolerance than others. However, there may be physiological tradeoffs during non-bleaching periods or across environmental gradients. The common Hawaiian reef-building coral, Montipora capitata, hosts the symbionts Cladocopium C31 and/or Durusdinium glynnii. Here, we measured growth of these holobionts over two months to test whether the higher heat tolerance of D. glynnii involved a tradeoff of lower growth, which could impact survivorship and competition for space on the reef. Additionally, we tested whether any such tradeoffs were modulated by light, which is a major driver of the ecological distribution of these symbionts in Kāneʻohe Bay. During the first month, when water temperatures were warmer (median 25.5 °C), there was no effect of symbiont on growth. However, over the cooler second month (median 23.4 °C), C31-dominated corals grew up to 77% faster than D. glynnii-dominated corals, and this growth advantage increased in higher light treatments (up to a daily light integral of 3.8 mol m−2 d−1, corresponding to 3.8–6.4 m depth). This advantage may explain why C31-dominated colonies are more prevalent at most depths; however, their increasing advantage at higher light levels is not reflected in the shallowest parts of Kāneʻohe Bay, where D. glynnii-dominated colonies become more prevalent. This may indicate that in these warmer surface waters, D. glynnii's higher heat tolerance outweighs the growth advantage that would otherwise favor C31 during the cooler parts of the year, providing a net ecological benefit. As oceans continue to warm, understanding how symbionts and the environment mediate coral performance outcomes will help predict reef futures and inform conservation interventions where coral stocks are selected for specific traits or symbionts. [ABSTRACT FROM AUTHOR]

Reef-building corals host diverse dinoflagellate algal symbionts (Family Symbiodiniaceae) whose identity can influence host thermotolerance and whose relative abundance can be dynamic. Breakdown in this symbiosis during "bleaching" events can promote changes in symbiont communities in favour of thermotolerant types, particularly in the genus Durusdinium. We employed experimental bleaching to manipulate the symbiont communities of three common Caribbean reef-building species (Montastraea cavernosa, Orbicella faveolata, and Siderastrea siderea) and tested whether seasonal differences in the corals' symbiont communities at the time of their collection affected their responses to manipulation. In O. faveolata and S. siderea, a minimum threshold of initial background proportion Durusdinium trenchii shaped recovery from bleaching with mainly Durusdinium. In contrast, in M. cavernosa, Durusdinium became highly dominant after recovery even when it was undetectable prior to bleaching. Seasonal changes were also detected in M. cavernosa and S. siderea dominated by Cladocopium, with significant increases and decreases, respectively, in symbionts per host cell in October (following annual temperature maxima) compared to the previous April (following temperature minima). These results demonstrate how background symbionts and seasonal differences in symbiont density can affect the disturbance and recovery dynamics of algal symbiont communities in different coral species, and prompt further research into how seasonal changes in algal symbiosis might inform projected future bleaching, which is increasingly relevant in light of predicted winter warming and prolonged warm summer temperatures under climate change. [ABSTRACT FROM AUTHOR]

Reef corals have been threatened by climate change, with more frequent and intense bleaching events leading to extensive coral mortality and loss of coral cover worldwide. In the face of this, the corals' photosymbiont assemblages have received special attention as a key to better understand the bleaching process and its recovery. To assess the effects of thermal anomalies, the coral Mussismilia harttii and the hydrocoral Millepora alcicornis were monitored through the El Niño 2015/2016 at a Southwestern Atlantic (SWA) coral reef. A severe bleaching event (57% of colonies bleached) was documented, triggered by a < 3 °C-week heatwave, but no mortality was detected. The hydrocoral was more susceptible than the scleractinian, displaying bleaching symptoms earlier and experiencing a longer and more intense bleaching event. The composition of photosymbionts in the M. alcicornis population was affected only at the rare biosphere level (< 5% relative abundance), with the emergence of new symbionts after bleaching. Conversely, a temporary dysbiosis was observed in the M. harttii population, with one of the dominant symbiodiniaceans decreasing in relative abundance at the peak of the bleaching, which negatively affected the total β-diversity. After colonies' complete recovery, symbiodiniaceans' dominances returned to normal levels in both hosts. These results highlight critical differences in how the two coral species cope with bleaching and contribute to the understanding of the role of photosymbionts throughout the bleaching-recovery process. [ABSTRACT FROM AUTHOR]

Coral reefs are under threat from cumulative impacts such as cyclones, crown-of-thorns starfish (COTS) outbreaks and climate-driven coral bleaching events. Branching corals are more severely impacted by these events than other coral morphologies due to their sensitivity to heat stress and weaker skeletons and COTS preferred prey. The central Great Barrier Reef experienced unprecedented back-to-back bleaching events in 2016 and 2017. This study commenced in 2017 at the peak of heat stress and examined the impact of the heatwave on the survival and recovery of corals by assessing the growth, health (based on the visual health index) and physiological parameters (chlorophyll a, zooxanthellae density, lipid and protein content) of two species, Acropora millepora and Pocillopora acuta (N = 60 colonies for each species). It was conducted across a gradient of turbidity at three reefs, Pandora, Orpheus and Rib, that experienced in April 2017, degree heating weeks (DHW) of 9, 8 and 7, respectively. Orpheus experienced the worst bleaching, based on visual health score, followed by Rib and Pandora. Rib experienced the greatest mortality (78% by Nov 2017); however, this was attributed to the presence of actively feeding crown-of-thorns starfish. Growth rates of A. millepora were almost twice the rate of P. acuta. Both species showed significant seasonal variation with growth of A. millepora and P. acuta 35–40% and 23–33% significantly greater in the summer, respectively. Differences in growth rates were best explained by indicators of energy acquisition. For example, the most important predictor variable in determining higher growth rates and visual health score in A. millepora was chlorophyll a content. For P. acuta, visual health score was the best predictor variable for higher growth rates. This study highlights the important role that chlorophyll a and associated symbionts play in growth and survival in these corals during and after a heat stress event. [ABSTRACT FROM AUTHOR]

Over the past decade, an abundance of 16S rRNA gene surveys have provided microbiologists with data regarding the prokaryotes present in a coral-associated microbial community. Functional gene studies that provide information regarding what those microbes might do are fewer, particularly for non-tropical corals. Using the GeoChip 5.0S microarray, we present a functional gene study of microbiomes from five species of cold-water corals collected from depths of 296–1567 m. These species included two octocorals, Acanthogorgia aspera and Acanthogorgia spissa, and three stony corals: Desmophyllum dianthus, Desmophyllum pertusum (formerly Lophelia pertusa), and Enallopsammia profunda. A total of 24,281 gene sequences (representing different microbial taxa) encoding for 383 functional gene families and representing 9 metabolic gene categories were identified. Gene categories included metabolism of carbon, nitrogen, phosphorus, and sulfur, as well as virulence, organic remediation, metal homeostasis, secondary metabolism and phylogeny. We found that microbiomes from Acanthogorgia spp. were the most functionally distinct but also least diverse compared against those from stony corals. Desmophyllum spp. microbiomes were more similar to each other than to E. profunda. Of 383 total gene families detected in this study, less than 20% were significantly different among these deep-water coral species. Similarly, out of 59 metabolic sub-categories for which we were able to make a direct comparison to microbiomes of tropical corals, only 7 were notably different: anaerobic ammonium oxidation (anammox), chitin degradation, and dimethylsulfoniopropionate (DMSP) degradation, all of which had higher representations in deep-water corals; and chromium homeostasis/resistance, copper homeostasis/resistance, antibiotic resistance, and methanogenesis, all of which had higher representation in tropical corals. This implies a broad-scale convergence of the microbial functional genes present within the coral holobiont, independent of coral species, depth, symbiont status, and morphology. [ABSTRACT FROM AUTHOR]