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Many species establish symbiotic partnerships with different organisms to benefit energetically from living together to fit into environments, and such symbiosis is frequently found in the modern ocean as well as throughout Earth's history. For example, coral reef ecosystems represent one of the most productive and biologically diverse ecosystems in the modern ocean, which is simply explained by an assumption that many autotroph-heterotroph symbiotic species found in there increase the efficiency of trophic transfer from primary producers (i.e., algal symbionts) to primary consumers (i.e., animal hosts), and that such high efficiency may be propagated to entire food webs. However, this high efficiency has not been proved and illustrated with quantitative data in the trophic transfer of photosynthates from algal symbionts to animal hosts. In the present study, we measured the energetic balance between degradation and biomass growth, which is a major factor of the efficiency of trophic transfer, based on the analysis of stable nitrogen isotope ratios of amino acids for several species including sea anemones, stony corals, zoanthids, and soft corals, that were bred under an autotrophic condition in a laboratory aquarium. The results confirm that the symbiosis indeed provides highly effective energy transfer of algal photosynthates to animal hosts, and allow us to quantify that the energy transfer in the symbiosis increases by approximately twice of that when non-symbiotic herbivorous species feed on primary producers. These results induce a new perspective that the effective energy transfer driven by symbiosis is a critical factor controlling the development of highly productive and biologically diverse ecosystems in the modern ocean as well as throughout Earth's history. [ABSTRACT FROM AUTHOR] more...

Coral reef declines have been documented since the 1980's from a variety of global and local stressors. Management resource tools are needed to preserve these fragile ecosystems from stressors, both known and unknown. Laboratory studies have shown microplastics (MP) to have negative effects on coral physiology, but their effects in a natural environment are not well understood. Thus, our primary objectives were to explore associations between MPs and coral reef attributes. We measured MP concentrations from sub-surface water and coral tissue samples from two Caribbean/Atlantic scleractinian coral species, Montastraea cavernosa and Orbicella faveolata, from St. John, U.S. Virgin Islands and Florida's Coral Reef in 2017 and 2018, respectively. Polymer identification yielded mostly cotton or polyester fibers for both water and coral tissue samples. This study is the first to document MPs in coral tissues from either the U.S. Virgin Islands or Florida's Coral Reef and is the first to explore how MPs relate to coral reef attributes. Significant, positive relationships were seen between MPs in coral tissue and coral density, rugosity, and percent coral cover, indicating MPs may not have immediate adverse effects on coral reef health. [ABSTRACT FROM AUTHOR] more...

Stony corals possess major components of the circadian system, which oscillate in response to light-dark cycles in aquatic environments. However, the extent to which the circadian system influences physiological processes remains unknown. This study investigated the role of circadian genes (cry1 , cry2 , cry3 , clock , cycle , and slmb) in modulating the transcription of photoreceptor (opsin1 , opsin2 , and opsin3), calcification/metabolism-related (ca , pmca , sglt , and ppp1r), and homeostasis/stress-related (hif1α , egln , sod , and hsp70) genes in Acropora digitifera , a stony coral inhabiting shallow water. Nubbins of A. digitifera were reared under light-dark (LD) and constant darkness (DD) conditions and sampled at 4-h intervals. Quantitative PCR analysis revealed that cry1 , cry2 , cry3 , and clock expression increased during the daytime under LD conditions and attenuated during the subjective daytime under DD conditions, suggesting that these genes are light-responsive. In contrast, cycle and slmb exhibited similar expression profiles with increases during the daytime/subjective daytime under both LD and DD conditions, implying robust roles in the circadian system. The abundance of opsin1 showed minimal change under LD and DD conditions, whereas the abundances of opsin2 and opsin3 increased during daytime/subjective daytime under both conditions, indicating circadian regulation. Some genes tested by qPCR significantly fluctuated with light (pmca , sglt , ppp1r , egln , sod , and hsp70) and time (ca , pmca , sglt , ppp1r , hif1α , egln , sod , and sod). Principal component analysis revealed significant correlations of circadian genes (cycle or slmb) with calcification/metabolism-related (pmca), oxygen homeostasis (hif1α), and stress indicator (sod) genes under both LD and DD conditions. Therefore, some physiological responses in A. digitifera exhibit daily changes and are partially regulated by the circadian system. [ABSTRACT FROM AUTHOR] more...

Sexually propagated scleractinian corals are in high demand for coral reef restoration. However, for threatened reef-building corals, many of the molecular mechanisms related to their reproduction remain largely unknown, which forms a major bottleneck in the large-scale cultivation of sexually reproducing corals. In this study, we analyzed the proteomic signatures of red eggs and spermatozoa from the ecologically significant coral Galaxea fascicularis, using a data-independent acquisition mass spectrometry (DIA-MS) method. A total of 7741 and 7279 proteins from mature red eggs and spermatozoa were identified, respectively. Among these proteins, 596 proteins were spermatozoa-specific and 1056 were egg-specific. Additionally, a total of 4413 differentially abundant proteins (DAPs) were identified, among which 3121 proteins were up-regulated in red eggs and 1292 proteins were up-regulated in spermatozoa. Furthermore, anenrichment analyses showed that DAPs identified in red eggs were mainly involved in the progesterone-mediated oocyte maturation pathway and lectin pathway; and DAPs detected in spermatozoa were mainly involved in the insulin secretion pathway and metabolic pathways for the generation of energy. This result will contribute to the discovery of the intrinsic regulation pathway of gamete maturation and fertilization. Furthermore, at least 57 proteins associated with gamete maturation and reproduction were identified, including the red fluorescent protein (RFP), vitellogenin proteins (VG), the egg protein (EP), the testis-specific serine/threonine-protein kinase family (TSSKs), and the EF-hand Ca2+-binding protein family (EFHC1 and EFHC2). Particularly, the third yolk protein EUPHY was reported for the first time in G. fascicularis. In conclusion, this study unveiled groundbreaking molecular insights into coral sexual reproduction, paving the way for more effective conservation and sustainable development of coral reef ecosystems [ABSTRACT FROM AUTHOR] more...

Photoreception is essential to coral growth, reproduction, and stress responses. Thus far, opsin-based photoreception and potential photoadaptation in Scleractinian corals remains unclear. This study used natural and light-emitting diode (LED) lighting to investigate how Acropora digitifera, which is adapted to shallow-water environments, responds to day–night conditions. We successfully cloned three opsin genes (Adopsin1, Adopsin2, and Adopsin3). Adopsin1 and Adopsin2 clustered with the Cnidopsins, whereas Adopsin3 clustered with the anthozoan-specific opsin I group. In situ hybridization showed positive signals of these genes in coral endodermal and ectodermal layers. When A. digitifera branches were reared under a day–night cycle with natural light, a day-high and night-low pattern was observed in the transcript levels of Adopsin1 and Adopsin3. Genes related to calcification [plasma membrane calcium transporting ATPase 2 (PMCA)] and oxygen homeostasis regulation [hypoxia-inducible factor 1 alpha (HIF1α)] showed similar patterns. Rearing of branches under a day–night cycle (photoperiod = 12:12, 26.5–29.3 μmol s−1 m−2) with red (λmax = 628 nm), but not blue (464 nm) or green (519 nm) LED lighting led to increases in transcript levels of Adopsin1 and Adopsin3 during photophase. The transcript levels of carbonic anhydrase, PMCA, HIFα, and sodium-glucose cotransporter were significantly higher during photophase than during scotophase. Furthermore, Adopsin3 upregulation occurred within 4 h of exposure to a red LED light at night. These results suggest that A. digitifera can responding to long wavelengths of light, which play a crucial role in the photophysiology of the coral host. The capacity to perceive red light provides advantages in physiological adaptation and ecological niche occupation by A. digitifera in shallow waters. [ABSTRACT FROM AUTHOR] more...

Recent studies have revealed that stony corals create their extracellular skeletons via biologically controlled calcification, in which amorphous calcium carbonate (ACC), regarded as precursors of aragonite crystals, have been observed at nanoscale using electron microscopy. However, the exact mechanism by which ACC is generated, and how it contributes to skeletal growth in coral calcifying tissue, remains enigmatic. The septal skeleton of an individual polyp is composed of radially aligned plates extending upward from the aboral calcifying tissue. This structure includes microstructure known as the centers of calcification (CoC). However, despite its importance, direct in vivo observation of septal growth has not been reported. Observations under transmitted illumination using polarized light microscopy on calcifying tissue of young Acropora digitifera revealed small crystals, a few micrometers in size, that accompany subtle movements and that emerge exclusively on the inner wall of the pocket in extracellular calcifying fluid (ECF). Crystal growth initiated from small, scattered crystals on a glass plate resembles this phenomenon observed in coral skeletons. Time-lapse photographs of 12 individuals in early primary polyp settlement revealed this process in three individuals, documenting 13 of these crystal events. This phenomenon occurred solely at the bases of subsequently formed septa. These crystals differ notably from fusiform crystals and from dumbbell-like or rod-like crystals growing individually. Upright two-photon microscopy captured movement of sub-micron-sized fluorescent calcein-accumulating particles, emphasizing their presence on the surface of the growing fronts of septa. Methodological advances that facilitate comprehensive in vivo observation of sub-micron-sized structures, calcein-accumulating particles to the skeleton, are needed to develop a more detailed understanding of coral skeletal growth. [ABSTRACT FROM AUTHOR] more...

Recent studies have predominantly spotlighted bacterial diversity within coral microbiomes, leaving coral-associated fungi in the shadows of scientific inquiry. This study endeavors to fill this knowledge gap by delving into the biodiversity, distribution and functional differences of fungi associated with soft corals Cladiella krempfi and Sarcophyton tortuosum, gorgonian coral Dichotella gemmacea and stony coral Favia speciosa from the South China Sea. Leveraging high-throughput sequencing of fungal internal transcribed spacer-1 (ITS1) region of the rRNA gene, a total of 431 fungal amplicon sequence variants (ASVs) were identified in this study, which indicated that a large number of fungal communities were harbored in the South China Sea corals. Noteworthy among our findings is that 10 fungal genera are reported for the first time in corals, with Candolleomyces, Exophiala, Fomitopsis, Inaequalispora, Kneiffiella, Paraphaeosphaeria, and Yamadazyma belonging to the Ascomycota, and Cystobasidium, Psathyrella, and Solicoccozyma to the Basidiomycota. Moreover, significant differences (p < 0.05) of fungal communities were observed among the various coral species. In particular, the gorgonian coral D. gemmacea emerged as a veritable haven for fungal diversity, boasting 307 unique ASVs. Contrastingly, soft corals S. tortuosum and C. krempfi exhibited modest fungal diversity, with 36 and 21 unique ASVs, respectively, while the stony coral F. speciosa hosted a comparatively sparse fungal community, with merely 10 unique ASVs in total. These findings not only provide basic data on fungal diversity and function in the South China Sea corals, but also underscore the imperative of nuanced conservation and management strategies for coral reef ecosystems worldwide. [ABSTRACT FROM AUTHOR] more...

Increasing ocean temperatures are causing dysbiosis between coral hosts and their symbionts. Previous work suggests that coral host gene expression responds more strongly to environmental stress compared to their intracellular symbionts; however, the causes and consequences of this phenomenon remain untested. We hypothesized that symbionts are less responsive because hosts modulate symbiont environments to buffer stress. To test this hypothesis, we leveraged the facultative symbiosis between the scleractinian coral Oculina arbuscula and its symbiont Breviolum psygmophilum to characterize gene expression responses of both symbiotic partners in and ex hospite under thermal challenges. To characterize host and in hospite symbiont responses, symbiotic and aposymbiotic O. arbuscula were exposed to three treatments: (1) control (18°C), (2) heat (32°C), and (3) cold (6°C). This experiment was replicated with B. psygmophilum cultured from O. arbuscula to characterize ex hospite symbiont responses. Both thermal challenges elicited classic environmental stress responses (ESRs) in O. arbuscula regardless of symbiotic state, with hosts responding more strongly to cold challenge. Hosts also exhibited stronger responses than in hospite symbionts. In and ex hospite B. psygmophilum both down‐regulated gene ontology pathways associated with photosynthesis under thermal challenge; however, ex hospite symbionts exhibited greater gene expression plasticity and differential expression of genes associated with ESRs. Taken together, these findings suggest that O. arbuscula hosts may buffer environments of B. psygmophilum symbionts; however, we outline the future work needed to confirm this hypothesis. [ABSTRACT FROM AUTHOR] more...

Generalists are thought to adapt to broader ecological conditions compared to less flexible specialists. However, few studies have systematically tested what ecological or life‐history traits are associated with organisms' ecological flexibility. Here, we used stony corals to test the relative effects of host traits and ecological factors on corals' flexibility to form photosymbioses with algae. We analysed data from 211 stony coral species to test if coral's geographic distribution, depth range, symbiont transmission mode or colony morphology predict coral–algal flexibility. We report a novel positive correlation between coral–algal flexibility and coral species' geographic range. Symbiont transmission mode was also a predictor of flexibility, albeit the result is less robust against sampling bias. Coral depth range and morphology did not show significant effects. We highlight that host–symbiont dispersal abilities, interactions and evolutionary histories likely contribute to the observed patterns. We urge conservation efforts to consider the ecological implications of coral–algal flexibility. [ABSTRACT FROM AUTHOR] more...

Members of the Cnidaria phylum were studied for centuries to depict the source of their unprecedented regeneration capacity. Although adult stem cells (ASCs) have been recognized in tissue growth/regeneration in many hydrozoans, there has not been any evidence of them in the ancestral Anthozoa class. This study sheds light on the development of epidermal epithelium expansion, akin to blastema, during tissue regeneration after small circular incisions (each 2.77 mm2) and during the natural expansion of tissue across a flat surface in the scleractinian coral Stylophora pistillata. Regeneration was completed within 9 days in 84.5% (n = 64) of the assays. About 35% of the samples regrew a single polyp, 60% showed no polyp regrowth, and approximately 6% exhibited multiple new polyps. We further used histological staining, pH3, Piwi immuno-histochemistry, and qPCR for eight stemness markers: Piwi-1, Nanos-1, Nanos-1-like, Tudor-5, Tudor-7, Boule, Sox-2, and Myc-1. The results revealed the formation of an "addendum", an epidermal epithelium in the growing edges (in regenerating and normal-growing fronts) inhabited by a cluster of small cells featuring dense nuclei, resembling ASCs, many expressing pH3 as well as Piwi proteins. Most of the stemness genes tested were upregulated. These results indicate the participation of ASCs-like cells in tissue regeneration and growth in scleractinian corals. [ABSTRACT FROM AUTHOR] more...

Multicellular eukaryotic organisms are hosts to communities of bacteria that reside on or inside their tissues. Often the eukaryotic members of the system contribute to high proportions of metagenomic sequencing reads, making it challenging to achieve sufficient sequencing depth to evaluate bacterial ecology. Stony corals are one such complex community; however, separation of bacterial from eukaryotic (primarily coral and algal symbiont) cells has so far not been successful. Using a combination of hybridization chain reaction fluorescence in situ hybridization and fluorescence activated cell sorting (HCR-FISH + FACS), we sorted two populations of bacteria from five genotypes of the coral Acropora loripes , targeting (i) Endozoicomonas spp, and (ii) all other bacteria. NovaSeq sequencing resulted in 67–91 M reads per sample, 55%–90% of which were identified as bacterial. Most reads were taxonomically assigned to the key coral-associated family, Endozoicomonadaceae, with Vibrionaceae also abundant. Endozoicomonadaceae were 5x more abundant in the ' Endozoicomonas ' population, highlighting the success of the dual-labelling approach. This method effectively enriched coral samples for bacteria with <1% contamination from host and algal symbionts. The application of this method will allow researchers to decipher the functional potential of coral-associated bacteria. This method can also be adapted to accommodate other host-associated communities. [ABSTRACT FROM AUTHOR] more...

The formation of skeletal structures composed of different calcium carbonate polymorphs (e.g. aragonite and calcite) appears to be both biologically and environmentally regulated. Among environmental factors influencing aragonite and calcite precipitation, changes in seawater conditions—primarily in the molar ratio of magnesium and calcium during so‐called 'Calcite' (mMg:mCa below 2) or 'Aragonite' seas (mMg:mCa above 2)—have had profound impacts on the distribution and performance of marine calcifiers throughout Earth's history. Nonetheless, the fossil record shows that some species appear to have counteracted such changes and kept their skeleton polymorph unaltered. Here, the aragonitic octocoral Heliopora coerulea and the aragonitic scleractinian Montipora digitata were exposed to Calcite Sea‐like mMg:mCa with various levels of magnesium and calcium concentration, and changes in both the mineralogy (i.e. CaCO3 polymorph) and gene expression were monitored. Both species maintained aragonite deposition at lower mMg:mCa ratios, while concurrent calcite presence was only detected in M. digitata. Despite a strong variability between independent experimental replicates for both species, the expression for a set of putative calcification‐related genes, including known components of the M. digitata skeleton organic matrix (SkOM), was found to consistently change at lower mMg:mCa. These results support the previously proposed involvements of the SkOM in counteracting decreases in seawater mMg:mCa. Although no consistent expression changes in calcium and magnesium transporters were observed, down‐regulation calcium channels in H. coerulea in one experimental replicate and at an mMg:mCa of 2.5, pointing to a possible active calcium uptake regulation by the corals under altered mMg:mCa. [ABSTRACT FROM AUTHOR] more...

Whereas post-mortem bioerosional features such as bivalve, sponge or worm borings are frequently preserved in ancient corals, reports of ante-mortem skeletal anomalies on Cretaceous specimens are rare. Here, we document the occurrence of fossil skeletal lesions produced during the life span of the colonies in exceptionally wellpreserved Aptian (Early Cretaceous) scleractinians from the Maestrat Basin (East Iberia). These ante-mortem damage features are characterized by millimetric to centimetric areas of skeletal depression, as well as upward growth around damaged areas indicating regeneration. Depressed skeletal lesions are commonly overprinted by post-mortem lithophagid borings. Distribution of skeletal anomalies on the colonies can be focal or multifocal, and their location basal, medial and/or apical. The extent of the skeletal anomalies can be mild (occupying <10% of the colony) to extreme (occupying =50% of the colony). The edges of the skeletal anomalies are distinct (disk-shaped) or annular (ring-shaped), the margins are mainly smooth to uneven, and the shapes are circular, oblong, pyriform, linear, or irregular. The skeletal anomalies exhibited by the corals are comparable to tissue lesions produced in modern corals either by predation, bioerosion or disease, which may be followed by skeletal overgrowth or denudation. Although demonstrating disease in fossil colonies is challenging, there is no reason to believe that corals did not experience diseases back in the Cretaceous. This paper gives an example of the potential of coral anomalies originating from tissue lesions and skeletal damage to be preserved in the geological record, a factor that may have been often overlooked in the study of fossil coral communities. [ABSTRACT FROM AUTHOR] more...

Stony corals (Order: Scleractinia) are central to vital marine habitats known as coral reefs. Numerous stressors in the Anthropocene are contributing to the ongoing decline in coral reef health and coverage. While viruses are established modulators of marine microbial dynamics, their interactions within the coral holobiont and impact on coral health and physiology remain unclear. To address this key knowledge gap, we investigated diverse stony coral genomes for 'endogenous' viruses. Our study uncovered a remarkable number of integrated viral elements recognized as 'Polintoviruses' (Class Polintoviricetes) in thirty Scleractinia genomes; with several species harboring hundreds to thousands of polintoviruses. We reveal massive paralogous expansion of polintoviruses in stony coral genomes, alongside the presence of integrated elements closely related to Polinton-like viruses (PLVs), a group of viruses that exist as free virions. These results suggest multiple integrations of polintoviruses and PLV-relatives, along with paralogous expansions, shaped stony coral genomes. Re-analysis of existing gene expression data reveals all polintovirus structural and non-structural hallmark genes are expressed, providing support for free virion production from polintoviruses. Our results, revealing a significant diversity of polintovirus across the Scleractinia order, open a new research avenue into polintovirus and their possible roles in disease, genomic plasticity, and environmental adaptation in this key group of organisms [ABSTRACT FROM AUTHOR] more...

Background: Nucleic acid-based analytical methods have greatly expanded our understanding of global prokaryotic diversity, yet standard metabarcoding methods provide no information on the most fundamental physiological state of bacteria, viability. Scleractinian corals harbour a complex microbiome in which bacterial symbionts play critical roles in maintaining health and functioning of the holobiont. However, the coral holobiont contains both dead and living bacteria. The former can be the result of corals feeding on bacteria, rapid swings from hyper- to hypoxic conditions in the coral tissue, the presence of antimicrobial compounds in coral mucus, and an abundance of lytic bacteriophages. Results: By combining propidium monoazide (PMA) treatment with high-throughput sequencing on six coral species (Acropora loripes, A. millepora, A. kenti, Platygyra daedalea, Pocillopora acuta, and Porites lutea) we were able to obtain information on bacterial communities with little noise from non-viable microbial DNA. Metabarcoding of the 16S rRNA gene showed significantly higher community evenness (85%) and species diversity (31%) in untreated compared with PMA-treated tissue for A. loripes only. While PMA-treated coral did not differ significantly from untreated samples in terms of observed number of ASVs, > 30% of ASVs were identified in untreated samples only, suggesting that they originated from cell-free/non-viable DNA. Further, the bacterial community structure was significantly different between PMA-treated and untreated samples for A. loripes and P. acuta indicating that DNA from non-viable microbes can bias community composition data in coral species with low bacterial diversity. Conclusions: Our study is highly relevant to microbiome studies on coral and other host organisms as it delivers a solution to excluding non-viable DNA in a complex community. These results provide novel insights into the dynamic nature of host-associated microbiomes and underline the importance of applying versatile tools in the analysis of metabarcoding or next-generation sequencing data sets. [ABSTRACT FROM AUTHOR] more...

Coral communities can survive in stressful environments; however, the mechanisms corals employ to endure challenging conditions are poorly understood. This study assessed how the heterotrophy of three coral genera (Acropora spp., Porites spp. and Platygyra spp.) varies among sites in the Dampier Archipelago, Western Australia, exposed to different levels of turbidity. Stable isotope δ13C and δ15N analysis of coral host and endosymbionts were combined with modern Bayesian isotopic niche analysis to demonstrate that heterotrophy in all three coral genera increased in highly turbid environments. While all coral genera were found to be more heterotrophic in highly turbid waters, Porites spp. favoured heterotrophy across all levels of turbidity, whereas Platygyra spp. and Acropora spp. were less heterotrophic at sites with lower turbidity. Thus, some scleractinian corals can alter their feeding strategies in response to turbidity levels. As nearshore coral reefs experience increased and prolonged turbidity with intensifying climate change and anthropogenic development, the knowledge gained from this study will allow for improved environmental impact assessment and predictive modelling for future coral reef conservation. [ABSTRACT FROM AUTHOR] more...

Stony corals (Scleractinia) are in the Phylum Cnidaria (cnidae referring to various types of stinging cells). They may be solitary or colonial, but all secrete an external, supporting aragonite skeleton. Large, colonial members of this phylum are responsible for the accretion of coral reefs in tropical and subtropical waters that form the foundations of the most biodiverse marine ecosystems. Coral reefs worldwide, but particularly in the Caribbean, are experiencing unprecedented levels of disease, resulting in reef degradation. Most coral diseases remain poorly described and lack clear case definitions, while the etiologies and pathogenesis are even more elusive. This introductory guide is focused on reef-building corals and describes basic gross and microscopic lesions in these corals in order to serve as an invitation to other veterinary pathologists to play a critical role in defining and advancing the field of coral pathology. [ABSTRACT FROM AUTHOR] more...

Standing genetic variation is a major driver of fitness and resilience and therefore of fundamental importance for threatened species such as stony corals. We analyzed RNA-seq data generated from 132 Montipora capitata and 119 Pocillopora acuta coral colonies collected from Kāneʻohe Bay, Oʻahu, Hawaiʻi. Our goals were to determine the extent of colony genetic variation and to study reproductive strategies in these two sympatric species. Surprisingly, we found that 63% of the P. acuta colonies were triploid, with putative independent origins of the different triploid clades. These corals have spread primarily via asexual reproduction and are descended from a small number of genotypes, whose diploid ancestor invaded the bay. In contrast, all M. capitata colonies are diploid and outbreeding, with almost all colonies genetically distinct. Only two cases of asexual reproduction, likely via fragmentation, were identified in this species. We report two distinct strategies in sympatric coral species that inhabit the largest sheltered body of water in the main Hawaiian Islands. These data highlight divergence in reproductive behavior and genome biology, both of which contribute to coral resilience and persistence. [ABSTRACT FROM AUTHOR] more...

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

This article discusses the use of assisted evolution techniques to enhance the bleaching tolerance of coral reefs. Coral reefs are facing numerous threats, including global warming, which disrupts the symbiotic relationship between coral and microalgae and leads to bleaching and potential death of coral. The study focuses on manipulating the genetic variants of algal symbionts to enhance their thermotolerance and their ability to provide vital nutrients to coral hosts. The researchers found that heat-evolved strains of Cladocopium proliferum improved thermal tolerance in adult corals and demonstrated high growth rates. This research offers hope for the future of coral conservation and may be crucial in mitigating the impacts of global change on coral reef ecosystems. [Extracted from the article] more...

The impact of changing nutrient conditions on scleractinian coral-based geochemical proxies is poorly understood, despite the nutrient balance in many coral reefs being disturbed by anthropogenic activity. Here, the geochemical responses of tropical corals Acropora polystoma and Porites lichen to nutrient enrichment and depletion are examined following growth under cultured conditions, to assess the impact of nutrients on traditional geochemical proxies for both temperature and the coral internal carbonate system. The corals were exposed to four different nutrient treatments over a period of 140 days: (1) a replete treatment with optimal levels of nitrate (∼4.5 μM) and phosphate (∼0.6 μM), (2) a nutrient depleted treatment with negligible nitrate and phosphate, (3) a treatment with high nitrate (∼73 μM) and negligible phosphate, and (4) a treatment with high phosphate (∼5.7 μM) and negligible nitrate. Results suggest nutrients play a hitherto under-appreciated role in coral skeleton elemental (Li/Ca, B/Ca, Mg/Ca, Sr/Ca, Li/Mg) and isotopic (δ11B) composition, with the internal carbonate chemistry also impacted. For example, Mg/Ca and Sr/Ca are lower, and Li/Mg higher, in the nutrient imbalanced and deplete treatments compared to the replete treatment for both species. Disruption to the carbonate system in corals cultured under imbalanced nutrient conditions is best explained by a decrease in dissolved inorganic carbon flux to the extracellular calcifying medium. Variations in nutrient concentration — or nutrient imbalance — can have dramatic consequences on both reconstructed sea surface temperatures and ocean or calcification pH, with reconstructed temperatures varying from −7°C to +52 °C, and δ11B-derived pH by up to 0.13 pH units. The impact from anthropogenically-induced nutrient disturbances should therefore be considered when generating temporal records of environments using coral skeletal archives. [ABSTRACT FROM AUTHOR] more...

The effects of sunscreen on scleractinian corals have garnered widespread attention; however, the toxic effects and mechanisms remain unclear. This study investigated the toxicological effects of two common inorganic filters used in sunscreens, nano zinc oxide and titanium dioxide (nZnO and nTiO₂), on the reef-building coral Galaxea fascicularis , focusing on the phenotypic, physiological, and transcriptomic responses. The results showed that after exposure to 0.8 mg/L of nZnO and 30 mg/L of nTiO₂ for 48 h, all coral polyps exhibited retraction. Zn and Ti ions were detected in coral tissues at concentrations of 67.18 and 24.87 μg/g, respectively, indicating the accumulation of nZnO and nTiO 2 in coral tissues. The zooxanthellae density, Fv/Fm , and chlorophyll- a content decreased significantly. The activity of antioxidant enzymes showed an increasing trend. Meanwhile, glutamine synthetase and glutamate dehydrogenase activities exhibited a decreasing trend. The health status of corals was impacted as a result of nZnO and nTiO 2 stress. Transcriptomic analysis showed that the toxicity mechanisms of nZnO and nTiO 2 differed in corals. Following exposure to nZnO, differentially expressed genes (DEGs) in corals were mainly enriched in signaling pathways related to immune response. The genes related to innate immunity, such as MASP1, MUC5AC, TLRs, and C2, were significantly upregulated, indicating that nZnO exposure induces an innate immune response in corals. Meanwhile, following nTiO 2 exposure, the upregulated DEGs were mainly enriched in signaling pathways related to transporter activity. In contrast, the downregulated DEGs were mainly enriched in energy metabolism pathways, indicating that nTiO 2 disrupted the energy supply of corals, thereby leading to an increased demand for nutrient transport. This study reveals the toxic effects of nZnO and nTiO 2 , and their mechanisms of action on scleractinian corals, providing a reference for further assessing the toxicity of sunscreen on corals. [Display omitted] • 48h exposure to 800 μg/L nZnO or 30 mg/L nTiO 2 causes complete retraction of Galaxea fascicularis polyps. • nZnO activates coral immune response, severely disrupting physiological functions. • nTiO₂ exposure blocks coral energy supply, raising coral nutritional requirements. • nZnO exhibits a more significant inhibitory effect on G. fascicularis. [ABSTRACT FROM AUTHOR] more...

The rapid origination and diversification of major animal body plans during the early Cambrian coincide with the rise of Earth's first animal‐built framework reefs. Given the importance of scleractinian coral reefs as ecological facilitators in modern oceans, we investigate the impact of archaeocyathan (Class Archaeocyatha) reefs as engineered ecosystems during the Cambrian radiation. In this study, we present the first high‐resolution, three‐dimensional (3D) reconstructions of branching archaeocyathide (Order Archaeocyathida) individuals from three localities on the Laurentian paleocontinent. Because branched forms in sponges and corals display phenotypic plasticity that preserve the characteristics of the surrounding growth environment, we compare morphological measurements from our fossil specimens to those of modern corals to infer the surface conditions of Earth's first reefs. These data demonstrate that archaeocyaths could withstand and influence the flow of water, accommodate photosymbionts, and build topographically complex and stable structures much like corals today. We also recognize a stepwise increase in the roughness of reef environments in the lower Cambrian, which would have laid a foundation for more abundant and diverse coevolving fauna. [ABSTRACT FROM AUTHOR] more...

Coral reefs are ecosystems under increasing threat from global climate change. Coral restoration is a tool for preserving the biological and ecological function of coral reefs by mitigating coral loss and maintaining the structural integrity and complexity of reefs. To generate the necessary stock for coral restoration, larger coral colonies are usually fragmented to generate smaller specimens for outplanting, taking advantage of the high regenerative ability of corals. In this study, we utilized RNA‐seq technology to understand the physiological responses of Porites lobata colonies to physical fragmentation and outplanting, which have thus far not been characterized. Our results demonstrate that P. lobata fragments undergoing physical injury recover through two distinct phases: rapid wound regeneration of the cut margins, followed by a slower growth phase that cements the colony to the substrate. Our study found rapid physiological responses to acute physical injury and outplanting in the coral host that involved significantly increased energy production, calcium homeostasis disruption, and endoplasmic reticulum (ER) stress leading to increased antioxidant expression and rates of protein turnover. Our results suggest that phosphoinositide‐mediated acute calcium homeostasis disruption stimulates wound recovery processes in response to physical injury. Symbiont gene expression revealed extremely low gene differences in response to fragmentation, growth, and outplanting. These results provide insight into the physiological mechanisms that allow for rapid wound healing and stabilization in response to physical injury in corals. [ABSTRACT FROM AUTHOR] more...

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

It is thought that the active physiological regulation of the chemistry of a parent fluid is an important process in the biomineralization of scleractinian corals. Biological regulation of calcification fluid pH (pHCF) and other carbonate chemistry parameters ([CO32−]CF, DICCF, and ΩCF) may be challenged by CO2 driven acidification and temperature. Here, we examine the combined influence of changing temperature and CO2 on calcifying fluid regulation in four common Caribbean coral species—Porites astreoides, Pseudodiploria strigosa, Undaria tenuifolia, and Siderastrea siderea. We utilize skeletal boron geochemistry (B/Ca and δ11B) to probe the pHCF, [CO32−]CF, and DICCF regulation in these corals, and δ13C to track changes in the sources of carbon for calcification. Temperature was found to not influence pHCF regulation across all pCO2 treatments in these corals, in contrast to recent studies on Indo-Pacific pocilloporid corals. We find that [DIC]CF is significantly lower at higher temperatures in all the corals, and that the higher temperature was associated with depletion of host energy reserves, suggesting [DIC]CF reductions may result from reduced input of respired CO2 to the DIC pool for calcification. In addition, δ13C data suggest that under high temperature and CO2 conditions, algal symbiont photosynthesis continues to influence the calcification pool and is associated with low [DIC]CF in P. strigosa and P. astreoides. In P. astreoides this effect is also associated with an increase in chlorophyll a concentration in coral tissues at higher temperatures. These observations collectively support the assertion that physicochemical control over coral calcifying fluid chemistry is coupled to host and symbiont physiological responses to environmental change, and reveals interspecific differences in the extent and nature of this coupling. [ABSTRACT FROM AUTHOR] more...

Fluorescence imaging of benthic communities is a widely used tool for determining the rate of hard coral recruitment in tropical reefs. Whilst fluorescent proteins are well-studied in scleractinian corals, less is understood about their distribution and function in other sessile reef invertebrates. This short study examines fluorescence images of benthic communities on Autonomous Reef Monitoring Structures (ARMS) from a remote and protected Indian Ocean reef system. We compare the abundance of adult and juvenile hard corals across three sites and between the topside and underside of ARMS recruitment plates. We also discuss observations of skeletal fluorescence in sponges, as well as uneven green fluorescent protein (GFP) concentrations across adult coral colonies. Our findings provide an insight into the recovery of shallow reefs previously hit by severe bleaching events and highlight the potential of ARMS fluorescence imaging for the analysis of cryptobenthic communities. [ABSTRACT FROM AUTHOR] more...

Biology, geology, and paleoclimatology studies of coral reefs often rely on annual rates of corallite extension determined from cores of skeletal material recovered from scleractinian corals. To examine how corallite orientation within such cores may affect measured extension rates, we used high-resolution X-ray computed axial tomography (CT) to image a suite of short Orbicella faveolata cores from corals living in the northwest Gulf of Mexico. This nondestructive method enabled skeletal extension rates to be determined several ways: (1) along transects that cross individual slice/slab images, (2) along transects that cross both a 0.6-mm-thick CT slice and the corresponding conventional X-ray image from a 8.4-mm-thick slab of skeletal material, and (3) along transects that cross slices/slab images oriented at varied angles relative to a coral core's longitudinal axis. Additionally, the true three-dimensional (3D) extension rates of individual corallites were determined and compared to the extension rates apparent on a two-dimensional (2D) slice/slab. Results suggest that differences between all methods are not statistically significant, confirming that the conventional extension rate methodology is suitable for studies if the core's longitudinal axis is appropriately aligned with the growth axis of the corallites. Effects of core misalignment on extension rates measurement and the appearance of skeletal structures in 2D images are described, and the applicability of 3D imagery for investigations of coral polyp growth patterns and coral colony development is demonstrated. [ABSTRACT FROM AUTHOR] more...

Background: The importance of symbiosis has long been recognized on coral reefs, where the photosynthetic dinoflagellates of corals (Symbiodiniaceae) are the primary symbiont. Numerous studies have now shown that a diverse assemblage of prokaryotes also make-up part of the microbiome of corals. A subset of these prokaryotes is capable of fixing nitrogen, known as diazotrophs, and is also present in the microbiome of scleractinian corals where they have been shown to supplement the holobiont nitrogen budget. Here, an analysis of the microbiomes of 16 coral species collected from Australia, Curaçao, and Hawai'i using three different marker genes (16S rRNA, nifH, and ITS2) is presented. These data were used to examine the effects of biogeography, coral traits, and ecological life history characteristics on the composition and diversity of the microbiome in corals and their diazotrophic communities. Results: The prokaryotic microbiome community composition (i.e., beta diversity) based on the 16S rRNA gene varied between sites and ecological life history characteristics, but coral morphology was the most significant factor affecting the microbiome of the corals studied. For 15 of the corals studied, only two species Pocillopora acuta and Seriotopora hystrix, both brooders, showed a weak relationship between the 16S rRNA gene community structure and the diazotrophic members of the microbiome using the nifH marker gene, suggesting that many corals support a microbiome with diazotrophic capabilities. The order Rhizobiales, a taxon that contains primarily diazotrophs, are common members of the coral microbiome and were eight times greater in relative abundances in Hawai'i compared to corals from either Curacao or Australia. However, for the diazotrophic component of the coral microbiome, only host species significantly influenced the composition and diversity of the community. Conclusions: The roles and interactions between members of the coral holobiont are still not well understood, especially critical functions provided by the coral microbiome (e.g., nitrogen fixation), and the variation of these functions across species. The findings presented here show the significant effect of morphology, a coral "super trait," on the overall community structure of the microbiome in corals and that there is a strong association of the diazotrophic community within the microbiome of corals. However, the underlying coral traits linking the effects of host species on diazotrophic communities remain unknown. 2iUFYDy-sBVn2WqgoVCqfb Video Abstract [ABSTRACT FROM AUTHOR] more...

Background Coral reefs house about 25% of marine biodiversity and are critical for the livelihood of many communities by providing food, tourism revenue, and protection from wave surge. These magnificent ecosystems are under existential threat from anthropogenic climate change. Whereas extensive ecological and physiological studies have addressed coral response to environmental stress, high-quality reference genome data are lacking for many of these species. The latter issue hinders efforts to understand the genetic basis of stress resistance and to design informed coral conservation strategies. Results We report genome assemblies from 4 key Hawaiian coral species, Montipora capitata, Pocillopora acuta, Pocillopora meandrina , and Porites compressa. These species, or members of these genera, are distributed worldwide and therefore of broad scientific and ecological importance. For M. capitata , an initial assembly was generated from short-read Illumina and long-read PacBio data, which was then scaffolded into 14 putative chromosomes using Omni-C sequencing. For P. acuta, P. meandrina , and P. compressa , high-quality assemblies were generated using short-read Illumina and long-read PacBio data. The P. acuta assembly is from a triploid individual, making it the first reference genome of a nondiploid coral animal. Conclusions These assemblies are significant improvements over available data and provide invaluable resources for supporting multiomics studies into coral biology, not just in Hawaiʻi but also in other regions, where related species exist. The P. acuta assembly provides a platform for studying polyploidy in corals and its role in genome evolution and stress adaptation in these organisms. [ABSTRACT FROM AUTHOR] more...

The recently exposed outcrops along the Dahan River in Shulin, northern Taiwan revealed diverse and abundant marine fossils including molluscs, shark and ray teeth, sand dollars, and otoliths from a wide range of fish taxa. In addition, numerous small and fragile fossil scleractinians were found and identified here as Dendrophyllia sp., from the mainly azooxanthellate (90%) dendrophylliid family. Lithology of the outcrops are mainly composed of grey sandstones from the Tapu Formation (Late Miocene), overlying on a layer of basaltic tuff. The absolute age of the boundary between the Tapu Formation and the underlying Nanchuang Formation is 8 Ma, which provides indications on the maximum age possible for the scleractinian fossils found in this study. Back then, the marine ecosystem in which the sampled Dendropyllia specimens grew was probably a turbid shallow coastal environment with muddy to sandy bottom, likely at the vicinity of a river estuary, as suggested by the combined presence of previously reported fish otoliths. To our knowledge, this is the first record of Dendrophyllia fossils from Taiwan. [ABSTRACT FROM AUTHOR] more...

Aim: How historical and contemporary eco‐evolutionary processes shape the patterns of genetic diversity and differentiation across species' distribution range remains an open question with strong conservation implications. Focusing on the orange stony coral, Astroides calycularis, we (a) characterized the pattern of neutral genetic diversity across the distribution range; (b) gave insights into the underlying processes; and (c) discussed conservation implications with emphasis on a national park located on a hotspot of genetic diversity. Location: South Mediterranean Sea and Zembra National Park. Methods: We combined new data from 12 microsatellites in 13 populations located in the Centre and in the Western Periphery of the distribution range with a published dataset including 16 populations from the Western and Eastern Peripheries. We analysed the relationship among parameters of genetic diversity (He, Ar(g)) and structure (population‐specific FST) and two measures of geographic peripherality. We compared two estimators of pairwise genetic structure (GST, DEST) across the distribution range. The evolutionary and demographic history of the populations following the Last Glacial Maximum was reconstructed using approximate Bayesian computations and maximum‐likelihood analyses. We inferred the contemporary connectivity among populations from Zembra National Park and with the neighbouring area of Cap Bon. Results: We demonstrate a decrease in genetic diversity and an increase in genetic differentiation from the Centre to the Eastern and Western Peripheries of the distribution range. Populations from Zembra show the highest genetic diversity reported in the species. We identified a spillover effect towards Cap Bon. Main conclusions: The patterns of genetic diversity and differentiation are most likely explained by "the postglacial range expansion hypothesis" rather than the "central–peripheral hypothesis." Enforcement of conservation measures should be considered to protect this genetic diversity pattern, in particular when considering the low effective population size inferred at many sites. [ABSTRACT FROM AUTHOR] more...

Abstract Background Scleractinian corals are important reef builders, but around the world they are under the threat of global climate change as well as local stressors. Molecular resources are critical for understanding a species’ stress responses and resilience to the changing environment, but such resources are unavailable for most scleractinian corals, especially those distributed in the South China Sea. We therefore aimed to provide transcriptome resources for 14 common species, including a few structure forming species, in the South China Sea. Description We sequenced the transcriptome of 14 species of scleractinian corals using high-throughput RNA-seq and conducted de novo assembly. For each species, we produced 7.4 to 12.0 gigabases of reads, and assembled them into 271 to 762 thousand contigs with a N50 value of 629 to 1427 bp. These contigs included 66 to 114 thousand unigenes with a predicted open reading frame, and 74.3 to 80.5% of the unigenes were functionally annotated. In the azooxanthelate species Tubastraea coccinea, 41.5% of the unigenes had at least a best-hit sequence from corals. In the other thirteen species, 20.2 to 48.9% of the annotated unigenes had best-hit sequences from corals, and 28.3 to 51.6% from symbiotic algae belonging to the family Symbiodinaceae. With these resources, we developed a transcriptome database (CoralTBase) which features online BLAST and keyword search for unigenes/functional terms through a user friendly Internet interface. Short conclusion We developed comprehensive transcriptome resources for 14 species of scleractinian corals and constructed a publicly accessible database (www.comp.hkbu.edu.hk/~db/CoralTBase). CoralTBase will facilitate not only functional studies using these corals to understand the molecular basis of stress responses and adaptation, but also comparative transcriptomic studies with other species of corals and more distantly related cnidarians. more...

Under current climate warming predictions, the future of coral reefs is dire. With projected coral reef decline, it is likely that coral specimens for bleaching research will increasingly become a more limited resource in the future. By adopting a holistic approach through increased collaborations, coral bleaching scientists can maximize a specimen’s investigative yield, thus reducing the need to remove more coral material from the reef. Yet to expand a specimen’s utility for additional analytic methods, information on how corals are collected is essential as many methods are variably sensitive to upstream handling and processing. In an effort to identify common practices for coral collection, sacrifice, preservation, and processing in coral bleaching research, we surveyed the literature from the last 6.5 years and created and analyzed the resulting dataset of 171 publications. Since January 2014, at least 21,890 coral specimens were collected for bleaching surveys or bleaching experiments. These specimens spanned 122 species of scleractinian corals where the most frequently sampled were Acropora millepora, Pocillopora damicornis, and Stylophora pistillata. Almost 90% of studies removed fragments from the reef, 6% collected skeletal cores, and 3% collected mucus specimens. The most common methods for sacrificing specimens were snap freezing with liquid nitrogen, chemical preservation (e.g., with ethanol or nucleic acid stabilizing buffer), or airbrushing live fragments. We also characterized 37 distinct methodological pathways from collection to processing of specimens in preparation for a variety of physiological, -omic, microscopy, and imaging analyses. Interestingly, almost half of all studies used only one of six different pathways. These similarities in collection, preservation, and processing methods illustrate that archived coral specimens could be readily shared among researchers for additional analyses. In addition, our review provides a reference for future researchers who are considering which methodological pathway to select to maximize the utility of coral bleaching specimens that they collect. [ABSTRACT FROM AUTHOR] more...

Terpios hoshinota is a black, encrusting sponge that hosts numerous symbiotic cyanobacteria in its tissues. The sponge often overgrows live scleractinian corals, thereby causing widespread and accelerated coral loss. However, our understanding of how subtropical waters influence the seasonal change in the progression rate of the sponge is poor. To elucidate the progression dynamics over a year, we obtained monthly measurements of linear progression of T. hoshinota (mm month−1) on the branching coral Montipora digitata in the subtropical waters of Sesoko Island, Okinawa, Japan from 2019 to 2020. The progression rate of T. hoshinota varied monthly throughout the year. The progression rates were the highest in summer (July, August, and October) with a mean value of 66 mm month−1, except in September, when strong typhoons came close to Okinawa and the progression rate decreased temporarily. The progression rates were the lowest in February 2020, at 9 mm month−1. The mean annual linear progression rate was estimated to be 28 mm month−1. Therefore, the progression dynamics of T. hoshinota could be linked to their growth mechanisms in relation to the seasonal changes in subtropical waters. [ABSTRACT FROM AUTHOR] more...

Deep-sea scleractinian cup corals are prominent members of Southern Ocean megabenthic communities, though little is known about their life history. This study used paraffin histology and scanning electron microscopy to characterize the reproduction of the scleractinian coral Balanophyllia malouinensis (Squires, 1961) from Burdwood Bank in the Drake Passage. Samples were taken in April and May via otter trawls, Blake trawls, and dredges on three separate cruises: one on the RV Lawrence M. Gould in 2006, and two on the RV Nathaniel B. Palmer in 2008 and 2011. B. malouinensis is gonochoric with rare hermaphroditism. All four spermatocyst stages were seen simultaneously in males; similarly, most females contained oocytes at varying stages of development, though seasonality or periodicity could not be determined without a wider range of sample dates. Average fecundity was 241 ± 184 oocytes/individual (n = 38) and not correlated to cup size. Maturing larvae were found in the mesenteries and coelenteron of females, indicating B. malouinensis broods its larvae. This study was the first to characterize the reproduction of a deep-sea Balanophyllia species and adds to a small but growing body of work seeking to understand the unique benthic communities of Burdwood Bank. [ABSTRACT FROM AUTHOR] more...

In the Persian Gulf, Azooxanthellate Scleractinia remain understudied compared to their symbiotic counterparts. Here, we report the presence of azooxanthellate coral Truncatoflabellum mortenseni (Cairns & Zibrowius, 1997) for the first time in Iranian deep waters. This species was found on soft sediments at depths of 83 and 101 m. Given this report, the distribution range of T. mortenseni, previously known to exist only in the Indonesian-Philippine regions, is now expanded to the Persian Gulf. [ABSTRACT FROM AUTHOR] more...

Seawater temperature, salinity and carbonate chemistry have been shown to influence the uranium/calcium (U/Ca) ratios of scleractinian coral skeletons. This apparent sensitivity of U/Ca to multiple environmental parameters calls into question whether there is one environmental variable that most strongly controls coral U/Ca, and whether U/Ca can be straightforwardly applied as a paleoenvironmental proxy due to the tendency of environmental variables to covary in space and time. In this study, uranium concentration data from an existing compilation of tropical scleractinian coral U-series measurements is paired with environmental data from the World Ocean Atlas (WOA) and the Global Ocean Data Analysis Project (GLODAP) to examine the sensitivity of coral skeletal U/Ca to multiple seawater properties including temperature, salinity, pH, and saturation state. First, univariate linear regressions and multiple linear regressions were used to compare relationships between uranium and environmental parameters in the dataset with relationships observed in previous studies. Next, principal component analysis and regularized regression were used to identify the most likely predictors of coral U/Ca in order to create a multiple linear regression model. Results indicate that pH, O, alkalinity, and temperature are all significant predictors of uranium concentrations in coral. The magnitude and strength of relationships between U/Ca and environmental variables also differ across different genera. Seawater properties with strong correlations and small ranges make interpretation of these results difficult. However, results of these analyses indicate that U/Ca is dependent on multiple environmental parameters and that previously developed univariate regressions may be insufficient to characterize the full range of variables that influence coral [238U]. [ABSTRACT FROM AUTHOR] more...

Global warming and anthropogenic pressures present serious threats to coral reefs. Various stressors caused by human activities have been shown to negatively influence coral reproduction and recruitment. Because these threats are unlikely to abate in the immediate future, conservation projects involving larval release monitoring programmes are needed. Therefore, we measured larval release from captive colonies of a common Indo-Pacific reef coral, Seriatopora caliendrum, between October 2018 and December 2019. The largest larvae release event occurred in May 2019, and the smallest one occurred in September 2019. Several coral reproductive features demonstrated a close connection with seawater temperature. In contrast to prior studies conducted at the same institute with corals belonging to the same genus, of the same average size, originating from the same site, and cultured under the same conditions, we documented decreased fecundity of Seriatopora corals ex situ in 2018–2019. Various types of disturbance influence the study site from which corals were originally collected. We propose that local human activities and large-scale physical disturbances have negatively affected coral fecundity in southern Taiwan. [ABSTRACT FROM AUTHOR] more...

Both juvenile and adult life stages of the temperate scleractinian coral Oculina arbuscula are resilient to the effects of moderate ocean acidification (OA) in contrast to many tropical corals in which growth and calcification rates are suppressed. Here, potential mechanisms of resilience to OA related to photosynthetic physiology and inorganic carbon processing were studied in adult O. arbuscula colonies. After exposing colonies to ambient and elevated carbon dioxide (CO2) treatments for 7 weeks, photosynthetic performance was characterized using photosynthesis versus irradiance experiments, chlorophyll fluorescence kinetics, and algal pigment content. Inorganic carbon-processing capabilities were assessed by measurement of internal and external carbonic anhydrase activity of the coral host, internal carbonic anhydrase activity of symbiotic algae, and the reliance of photosynthesis on external carbonic anhydrase. Photosynthetic physiology was unaffected by OA ruling out the possibility that resilience was mediated by increased photosynthetic energy supply. Carbonic anhydrase activities were maintained at elevated CO2 suggesting no major rearrangements of the inorganic carbon-processing machinery, but this could be a sign of resilience since tropical corals often down-regulate carbonic anhydrases at high CO2. The general lack of effect of ocean acidification on these physiological traits suggests other characteristics, such as maintenance of calcifying fluid pH and ability to acquire energy from heterotrophy, may be more important for the resilience of O. arbuscula to OA. [ABSTRACT FROM AUTHOR] more...

Growth anomalies (GAs), a tumour-like disease affecting scleractinian corals, have been reported across the major reef systems of the Indo-Pacific and wider Atlantic regions, predominantly affecting Acropora and Porites species. In 2018, GAs were observed for the first time on Isopora palifera, an important observation from the isolated Cocos (Keeling) Islands in the East Indian Ocean, as the species is a key reef building coral at the atoll. In this study, the local distribution and abundance of GAs was quantified to determine if this occurrence could be classified as an outbreak, and the effects of this disease on I. palifera on reproductive potential and growth was described using histological and geochemical analysis. Growth anomalies were documented at 75% of sites and affected approximately one third of the I. palifera colonies examined. This disease compromises the biological and reproductive functioning of the host, as evidenced by a significant reduction in the density of oocytes, mesenteries, polyps, and zooxanthellae in infected tissues in comparison to healthy tissue. Furthermore, geochemical analysis indicates changes to key trace elements may be the result of bioerosion processes by infecting bacteria and the reprecipitation of calcite. The results of this study indicate the division of energy to the rapid skeletal development that characterises the disease, may have occurred at the detriment of the future reproductive potential of the population. [ABSTRACT FROM AUTHOR] more...

Spherulites are radial distributions of acicular crystals, common in biogenic, geologic, and synthetic systems, yet exactly how spherulitic crystals nucleate and grow is still poorly understood. To investigate these processes in more detail, we chose scleractinian corals as a model system, because they are well known to form their skeletons from aragonite (CaCO 3) spherulites, and because a comparative study of crystal structures across coral species has not been performed previously. We observed that all 12 diverse coral species analyzed here exhibit plumose spherulites in their skeletons, with well-defined centers of calcification (CoCs), and crystalline fibers radiating from them. In 7 of the 12 species, we observed a skeletal structural motif not observed previously: randomly oriented, equant crystals, which we termed "sprinkles". In Acropora pharaonis , these sprinkles are localized at the CoCs, while in 6 other species, sprinkles are either layered at the growth front (GF) of the spherulites, or randomly distributed. At the nano- and micro-scale, coral skeletons fill space as much as single crystals of aragonite. Based on these observations, we tentatively propose a spherulite formation mechanism in which growth front nucleation (GFN) of randomly oriented sprinkles, competition for space, and coarsening produce spherulites, rather than the previously assumed slightly misoriented nucleations termed "non-crystallographic branching". Phase-field simulations support this mechanism, and, using a minimal set of thermodynamic parameters, are able to reproduce all of the microstructural variation observed experimentally in all of the investigated coral skeletons. Beyond coral skeletons, other spherulitic systems, from aspirin to semicrystalline polymers and chocolate, may also form according to the mechanism for spherulite formation proposed here. Understanding the fundamental mechanisms of spherulite nucleation and growth has broad ranging applications in the fields of metallurgy, polymers, food science, and pharmaceutical production. Using the skeletons of reef-building corals as a model system for investigating these processes, we propose a new spherulite growth mechanism that can not only explain the micro-structural diversity observed in distantly related coral species, but may point to a universal growth mechanism in a wide range of biologically and technologically relevant spherulitic materials systems. Image, graphical abstract [ABSTRACT FROM AUTHOR] more...

Efforts to study the microbial communities associated with corals can be limited by inefficiencies in the sequencing process due to high levels of host amplification by universal bacterial 16S rRNA gene primers. Here, we develop an inexpensive peptide nucleic acid (PNA) clamp that binds to a target sequence of host DNA during PCR and blocks amplification. We then test the ability of this PNA clamp to mitigate host contamination and increase overall microbial sequence coverage on samples from three coral species: the gorgonians Eunicea flexuosa and Gorgonia ventalina, and the scleractinian Porites panamensis. The 20-bp PNA clamp was designed using DNA from E. flexuosa. Adding the PNA clamp during PCR increased the percentage of microbial reads in E. flexuosa samples more than 11-fold. Microbial community diversity was similar without- and with-PNA clamps, as were the relative frequencies of the ten most abundant ASVs (amplicon sequence variants), indicating that the clamps successfully blocked host DNA amplification while simultaneously increasing microbial DNA amplification proportionally across the most abundant taxa. The reduction of E. flexuosa DNA correlated with an increase in the abundance of rarer taxa. The clamp also increased the average percentage of microbial reads in another gorgonian, G. ventalina, by 8.6-fold without altering the microbial community beta diversity, and in a distantly related scleractinian coral, P. panamensis, by nearly double. The reduction of host contamination correlated with the number of nucleotide mismatches between the host amplicon and the PNA clamp. The PNA clamp costs as little as $0.48 per sample, making it an efficient and cost-effective solution to increase microbial sequence coverage for high-throughput sequencing of coral microbial communities. [ABSTRACT FROM AUTHOR] more...

To understand how environmental conditions and reproductive events affect coral energetic status, seasonal variations in lipid and fatty acid profiles of the common scleractinian coral, Acropora millepora, were studied from pre-spawning in November 2009 until post-spawning in November 2010 at Halfway Island (in the Keppel Island Group, Southern Great Barrier Reef, Australia). Seasonal chlorophyll levels, photosynthetically active radiation (PAR), rainfall and water temperature were major drivers of the overall coral lipid profile, and this was particularly pronounced in correlations with the important, high-energy lipid, triacylglycerol. This likely reflected changing food sources and feeding modes (i.e. phototrophy vs heterotrophy), which corresponds to the opportunistic feeding behaviour of corals. Water temperature was also a major influencer of the coral fatty acid profile. In particular, saturated fatty acids correlated positively with water temperature, while polyunsaturated fatty acids correlated negatively, reflecting cell membrane fluidity regulation, which is necessary for coral to tolerate changing temperatures. Spawning and maternal provisioning also proved to be a major driver of change in the coral lipid profile. The mass spawning events in spring for both 2009 and 2010 caused reductions in the important coral egg constituents: wax ester, triacylglycerol, phosphatidylcholine and fatty acid 10:0. Interestingly, lipid accumulation was significantly lower in the 2010 spawn compared to 2009, possibly due to lower PAR and chlorophyll levels, reflecting reduced photosynthetic activity and phytoplankton availability. Regardless, in 2010, resource provisioning to egg production was greater than in 2009, suggesting increased reproductive effort in the face of environmental stress. This study demonstrates the strong influence of opportunistic heterotrophy and autotrophy and maternal provisioning on the coral lipid profile. Such information is fundamental to understanding the environmental and biochemical processes underlying coral health and predicting how anomalous events and climate-driven changes will affect coral reef assemblages. [ABSTRACT FROM AUTHOR] more...

Coral reefs are highly diverse marine ecosystems increasingly threatened on a global scale. The foundation species of reef ecosystems are stony corals that depend on their symbiotic microalgae and bacteria for aspects of their metabolism, immunity, and environmental adaptation. Conversely, the function of viruses in coral biology is less well understood, and we are missing an understanding of the diversity and function of coral viruses, particularly in understudied regions such as the Red Sea. Here we characterized coral-associated viruses using a large metagenomic and metatranscriptomic survey across 101 cnidarian samples from the central Red Sea. While DNA and RNA viral composition was different across coral hosts, biological traits such as coral life history strategy correlated with patterns of viral diversity. Coral holobionts were broadly associated with Mimiviridae and Phycodnaviridae that presumably infect protists and algal cells, respectively. Further, Myoviridae and Siphoviridae presumably target members of the bacterial phyla Actinobacteria, Firmicutes, and Proteobacteria, whereas Hepadnaviridae and Retroviridae might infect the coral host. Genes involved in bacterial virulence and auxiliary metabolic genes were common among the viral sequences, corroborating a contribution of viruses to the holobiont's genetic diversity. Our work provides a first insight into Red Sea coral DNA and RNA viral assemblages and reveals that viral diversity is consistent with global coral virome patterns. [ABSTRACT FROM AUTHOR] more...

Background: Coral reefs are among the most diverse, complex and densely populated marine ecosystems. To survive, morphologically simple and sessile cnidarians have developed mechanisms to catch prey, deter predators and compete with adjacent corals for space, yet the mechanisms underlying these functions are largely unknown. Here, we characterize the histology, toxic activity and gene expression patterns in two different types of tentacles from the scleractinian coral Galaxea fascilcularis – catch tentacles (CTs), used to catch prey and deter predators, and sweeper tentacles (STs), specialized tentacles used for territorial aggression. Results: STs exhibit more mucocytes and higher expression of mucin genes than CTs, and lack the ectodermal cilia used to deliver food to the mouth and remove debris. STs and CTs also express different sensory rhodopsin-like g-protein coupled receptors, suggesting they may employ different sensory pathways. Each tentacle type has a different complement of stinging cells (nematocytes), and the expression in the two tentacles of genes encoding structural nematocyte proteins suggests the stinging cells develop within the tentacles. CTs have higher neurotoxicity to blowfly larvae and hemolytic activity compared to the STs, consistent with a role in prey capture. In contrast, STs have higher phospholipase A2 activity, which we speculate may have a role in inducing tissue damage during territorial aggression. The expression of genes encoding cytolytic toxins (actinoporins) and phospholipases also differs between the tentacle types. Conclusions: These results show that the same organism utilizes two distinct tentacle types, each equipped with a different venom apparatus and toxin composition, for prey capture and defense and for territorial aggression. [ABSTRACT FROM AUTHOR] more...

Successful reproduction and survival are crucial to the continuation and resilience of corals globally. As reef waters warm due to climate change, episodic largescale tropical storms are becoming more frequent, drastically altering the near shore water quality for short periods of time. Therefore, it is critical that we understand the effects warming waters, fresh water input, and run-off have on sexual reproduction of coral. To better understand the effects of these near shore stressors on Hawaiian coral, laboratory experiments were conducted at the Institute of Marine Biology to determine the independent effects of suspended sediment concentrations (100mgl-1 and 200mgl-1), lowered salinity (28h), and elevated temperature (31 °C) on the successful fertilization, larval survival, and settlement of the scleractinian coral Montipora capitata. In the present study, early developmental stages of coral were exposed to one of three near shore stressors for a period of 24 h and the immediate (fertilization) and latent effects (larval survival and settlement) were observed and measured. Fertilization success and settlement were not affected by any of the treatments; however, larval survival was negatively affected by all of the treatments by 50% or greater (p>0.05). These data show that early life stages of M. capitata may be impacted by near shore stressors associated with warming and more frequent storm events. [ABSTRACT FROM AUTHOR] more...

Strong physical disturbance from hurricanes can disrupt coral reef ecosystems and precipitate a regime shift toward algal dominance, particularly in the absence of grazing pressure to regulate algal growth post-storm. Here, we examine the influence of Hurricane Irma on a keystone grazer, Diadema antillarum, and the surrounding coral reef benthic community in the Florida Keys. D. antillarum densities and test diameters, as well as percent cover of coral reef benthic groups, were measured at 10 sites in the middle and upper Keys before and after Irma. Significant decreases in mean D. antillarum density and median test diameter were observed following the storm. There was a correlation between the magnitude of decline in D. antillarum density and the magnitude of sediment deposition on reefs, suggesting that abrasion or burial from sediment transport may have contributed to D. antillarum mortality. We detected significant decreases in the percent cover of sponges and hydrocorals following the storm, but no change in scleractinian coral cover, which was very low (3% mean cover) at the onset of the study. Macroalgal cover increased at sites in the upper Keys and decreased at sites in the middle Keys. There was no relationship between post-storm D. antillarum density and the change in percent cover of macroalgae or turf-algal-sediment matrix (TAS), likely due to low overall abundance of the grazer. We predict that coral reefs will remain in an algal-dominated ecosystem state due to, among other factors, increasing frequency of strong hurricanes that impact the D. antillarum population. [ABSTRACT FROM AUTHOR] more...

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

White Plague Type II (WPL II) is a disease increasingly affecting scleractinian coral species and progresses rapidly. However, the etiological pathogen and remedy remain elusive. In this study, transmission experiments demonstrated that Aureimonas altamirensis and Aurantimonas coralicida, representing the WPL II pathogens, could infect Pocillopora damicorni. The infection produced selected pathological symptoms, including bleaching, tissue loss, and decolorization. Furthermore, ammonia degradation significantly reduced the severity of infection by these pathogens, indicating that ammonia may be a virulence factor for WPL II. Coral microbiome analysis suggested that ammonia degradation mediates the anti-white plague effect by maintaining the density of Symbiodiniaceae and stabilizing the core and symbiotic bacteria. Aureimonas altamirensis and Aurantimonas coralicida have been shown to cause diseases of P. damicornis , with ammonia acting as a virulence factor, and ammoniac degradation may be a promising and innovative approach to mitigate coral mortality suffering from increasing diseases. [Display omitted] • Aureimonas altamirensis and Aurantimonas coralicida were identified as potential etiological agents of Pocillopora damicornis. • Ammonia was identified as a virulence factor of two pathogens of Pocillopora damicornis. • Ammoniac degradation could minimize coral mortality suffering from increasing diseases effectively. • Ammoniac degradation maintained the coral-associated microbiome and stabilized health indicators of corals from pathogens. [ABSTRACT FROM AUTHOR] more...