Chemical diversity of scleractinian corals revealed by untargeted metabolomics and molecular networking

The chemical diversity of scleractinian corals is closely related to their physiological,ecological,and evolutionary status,and can be influenced by both genetic background and environmental variables.To investigate intraspecific variation in the metabolites of these corals,the metabolomes of four species(Pocillopora meandrina,Seriatopora hystrix,Acropora formosa,and Fungia fungites)from the South China Sea were analyzed using untargeted mass spectrometry-based metabolomics.The results showed that a variety of metabolites,including amino acids,peptides,lipids,and other small molecules,were differentially distributed among the four species,leading to their significant separation in principal component analysis and hierarchical clustering plots.The higher content of storage lipids in branching corals(P.meandrina,S.hystrix,and A.formosa)compared to the solitary coral(F.fungites)may be due to the high densities of zooxanthellae in their tissues.The high content of aromatic amino acids in P.meandrina may help the coral protect against ultraviolet damage and promote growth in shallow seawater,while nitrogen-rich compounds may enable S.hystrix to survive in various challenging environments.The metabolites enriched in F.fungites,including amino acids,dipeptides,phospholipids,and other small molecules,may be related to the composition of the coral's mucus and its life-history,such as its ability to move freely and live solitarily.Studying the chemical diversity of scleractinian corals not only provides insight into their environmental adaptation,but also holds potential for the chemotaxonomy of corals and the discovery of novel bioactive natural products.

Diversity of symbiotic algae of the genus Symbiodinium in scleractinian corals of the Xisha Islands in the South China Sea

Symbiotic algae （Symbiodinium sp.） in scleractinian corals are important in understanding how coral reefs will respond to global climate change. The present paper reports on the diversity of Symbiodinium sp. in 48 scleractinian coral species from 25 genera and 10 families sampled from the Xisha Islands in the South China Sea, which were identified with the use of restriction fragment length polymorphism （RFLP） of the nuclear ribosomal DNA large subunit gene （rDNA）. The results showed that： （i） Symbiodinium Clade C was the dominant zooxanthellae in scleractinian corals in the Xisha Islands; （ii） Symbiodinium Clade D was found in the corals Montipora aequituberculata, Galaxea fascicularis, and Plerogyra sinuosa; and （iii） both Symbiodinium Clades C and D were found simultaneously in Montipora digitata, Psammocora contigua, and Galaxeafascicularis. A poor capacity for symbiosis polymorphism, as uncovered by RFLP, in the Xisha Islands indicates that the scleractinian corals have low adaptability to environmental changes. Further studies are needed to investigate zooxanthellae diversity using other molecular markers.

Triassic Scleractinian Corals in China：A Review of Present Knowledge

Scleractinian corals appeared during the Anisian period of the Triassic after the end-Permian mass extinction, which in Triassic were distinct from the Jurassic-Cretaceous scleractinian corals. The study on Triassic scleractinian coral fauna as a separate field is significant for exploring the development and evolution of modern corals and investigating environmental changes since the Mesozoic. The first Triassic coral in China was reported in 1925, and since then, nearly 25 articles dealing with taxonomy and 17 papers about fossil reports on Triassic scleractinian corals in China have been published, which refer to 60 genera and 312 species, 49 localities and 25 strata. In this paper, the history, taxonomy, localities, stratigraphic distribution, current research, and existing knowledge gaps of the Triassic scleractinian corals in China are reviewed. More specifically, the research findings of the Triassic scleractinain coral in China since 1925 are discussed; the species of the Triassic scleractian coral fossil reported in China, has been examined and its synonyms have been sorted out; the geographical distributions of the Middle and Late Triassic scleractinian corals in China are systematically treated; the Triassic coral biostratigraphy in China has been improved; and the stratigraphic ranges of existing genera and species are provided. The above conclusions are presented in the form of complete figures. At the same time, we analyzed shortcomings in current research and identified productive future research directions of the Triassic scleractinian corals in China.

Scleractinian coral communities of Hormuz Island in the PersianGulf

The abundance and health of scleractinian coral communities of Hormuz Island were investigated.For this purpose,we employed 20 m line intercept transects—12 in the intertidal zone and 15 subtidally to evaluate coral cover and community composition.The estimated dead coral coverage was 6.21%±0.81%,while live coral coverage was 16.93%±1.81%,considered as very poor.Totally,12 genera were recorded,of which Porites with 11.9%±1.4%live cover was the dominant,while Goniopora had the least cover(0.07%±0.08%).Based on Mann-Whitney U-test,live coral coverage,dead coral coverage,algal coverage,cover of other benthic organisms and abiotic components showed significant univariate differences between zones(p<0.05).The Spearman correlation test between the abundance of biotic and abiotic components indicated significant negative correlation of live coral and sand with zoantharian and significant positive correlation of algae and other benthic organisms with rubble.The reef health indices used for the corals indicated that,in general,the environmental conditions were not suitable,which could be attributed to both natural and anthropogenic factors,the most important of which was zoantharian’overgrowth on the scleractinian corals in this region.

Involvement of the ammonium assimilation mediated by glutamate dehydrogenase in response to heat stress in the scleractinian coral Pocillopora damicornis

Glutamate dehydrogenase(GDH)plays an important role in the ammonium assimilation and nitrogen metabolism by catalyzing the reversible oxidative deamination of L-glutamate toα-ketoglutarate.In the present study,the potential functions of GDH in response to heat stre ss were explored in the scleractinian coral Pocillopora damicornis(designated as PdGDH).The cDNA of PdGDH contained an open reading frame of 1611 bp encoding a polypeptide of 536 amino acids,which exhibited the highest sequence identity to GDH of Stylophora pistillata(96%identity),and the deduced PdGDH protein was predicted to contain one GdhA domain(from Val95 to Tyr525).The recombinant protein of PdGDH(rPdGDH)was expressed in Escherichia coli BL21(DE3)-Transetta,and its catalytic activity was measured under different temperatures,pH conditions and epigallocatechin-3-gallate(EGCG,a GDH inhibitor)concentrations.The purified rPdGDH only used reduced coenzyme nicotinamide adenine dinucleotide(NADH)as coenzyme,and its highe st activity was observed at 35℃and pH 7.5,re spectively.The rPdGDH activity was negatively correlated with the concentration of EGCG,and was inhibited by more than half(65%,P<0.05)at 10mol/L EGCG.No significant alteration of PdGDH mRNA expression was detected at 12 h after exposure to heat and ammonium(P>0.05).Furthermore,the activities of NADH-GDH in the scleractinian coral P.damicornis increased significantly at 12 h after the heat and ammonium stress,and the NADH-GDH activity in the heat stress group(32.66 U/mg,P<0.05)was significantly higher than that in the heat and ammonium stress group(11.26 U/mg).These results collectively suggested that PdGDH,as a homologue of glutamate dehydrogenase in the scleractinian coral P.damicornis,could respond to heat stress at the protein level,which would have ability to further promote ammonium assimilation to increase the heat acclimatization of the coral-Symbiodiniaceae symbiotic association.

A Rapid Assessment of Scleractinian and Non-Scleractinian Coral Growth Forms Along the Saudi Arabian Coast, Red Sea

In this study we assessed the current status of coral reefs along the Saudi Arabian coast of the Red Sea. Among the three growth forms of Acroporid corals, the branching forms were found to dominate in the Farassan Islands （44.55%±11.10% cover） fol-lowed by tabular forms in the Doga Islands （ranging between 18%±6.47% and 18.30%±9.47% cover）. Digitate forms were rarely found along the coast except at Maqna. Among the five growth forms of non-Acroporid corals, we observed maximum cover of branching forms in the Yanbu offshore area （58.89%±15.11% cover） followed by the Jeddah coast （24.76%±14.04% cover）. The Millepora spp., a non-Scleractinian coral, was abundant at all the near-shore sites, such as Jeddah （10.70%±8.21%） and A1-Wajh （9.81%±6.69%）. The live coral cover （including both Scleractinian and non-Scleractinian corals） of Saudi Red Sea coast was seen to be higher in the north and gradually decrease towards the south. Principal Component analysis showed that the contribution of Acro- porid corals was greater in the southern region than in the northem and middle regions, but vice-versa in the case of non-Acroporid corals. Bray-Curtis cluster analysis categorized all the study sites into two major clusters with 60% similarity. Among them, one cluster-forming sites from Maqna to Masturah （Northem region） and the second one comprised the middle and southem regions （Jeddah to Farassan Islands）, and one outlier Rabigh.

Revision of the Genus Conophyllia d'Orbigny 1849(Anthozoa, Scleractinia, Triassic) and Conophyllia from the Renacuo area of Gêrzê, Tibet

There have been divergent opinions on whether Conophyllia develops synapticulae and dissepiments since its erection in 1849, with different views existing on the morphology of columella in Conophyllia.This paper presents a comprehensive review of Conophyllia, and revises the diagnosis according to new material from the Renacuo area of Gêrzê, Tibet.The revised diagnosis emphasises the following features： solitary coral; abundant radial elements subequal in thickness, lateral faces with granules and synapticulae; parietal, papillar or incompact columella, a few species lacking in columella; developed dissepiments.Individuals of Conophyllia have laminar septa of Triadophyllum type in earlier ontogenetic stages, while their septa in later ontogenetic stages are more fenestrate.The geological and geographical distribution of this genus is discussed, with five species of Conophylliafrom the Renacuo area of Gêrzê, Tibet being described and illustrated, including one new species and two in open nomenclatue.

Spatial variations in the trophic status of Favia palauensis corals in the South China Sea:Insights into their different adaptabilities under contrasting environmental conditions

Scleractinian corals exhibit a dual trophic pattern of autotrophic photosynthesis and heterotrophic predation.However,whether corals can adjust their trophic status under contrasting environmental conditions remains unclear.In our study,70 scleractinian corals(Favia palauensis)were collected from Sanya and the Xisha and Nansha Islands in the South China Sea.We measured the zooxanthellae density(ZD)andδ^(13)C of zooxanthellae(δ^(13)C_(z))and host tissue(δ^(13)C_(h))and analyzed the difference betweenδ^(13)C_(h) andδ^(13)C_(z)(i.e.,△^(h-z)^(13)C).The relatively high ZD andδ^(13)C_(z) values in the samples from Sanya indicate that these corals might have higher photosynthetic rates and autotrophic abilities than those from Xisha and Nansha.In contrast,the relatively lowδ^(13)C_(h) and△^(h-z)^(13)C values in the samples from Xisha and Nansha suggest that these corals might have a higher heterotrophic ability than those from Sanya.In addition,we tested the coral tissue biomass and skeletalδ^(13)C(δ^(13)C_(s))in the samples from Sanya and examined their correlations with△^(h-z)^(13)C.The results showed a negative correlation,indicating that the more the organic material produced by the coral,the stronger its heterotrophic ability.Our results show that corals can adjust their trophic status under different environmental and physiological conditions,which is essential for increasing their adaptability to different environmental conditions.

Antagonism between coral pathogen Vibrio coralliilyticus and other bacteria in the gastric cavity of scleractinian coral Galaxea fascicularis

Scleractinian corals host numerous microbial symbionts with different types of interactions. The gastric cavity of scleractinian coral, as a semiclosed subenvironment with distinct chemical characteristics(e.g., dissolved O2, pH, alkalinity, and nutrients), harbors a distinct microbial community and a diverse array of bacteria that can be pathogenic or beneficial. Galaxea fascicularis is one of the dominant massive scleractinian coral species on inshore fringing reefs in the northern South China Sea.Although the abundance of coral-associated bacteria has been investigated in G. fascicularis, less is known about the microorganisms in the gastric cavity. In this study, we specially isolated cultivable bacterial strains from the gastric cavity of G.fascicularis collected from Hainan Island using a noninvasive sampling approach. Among the 101 representative bacterial strains, one Vibrio coralliilyticus strain, SCSIO 43001, was found to be a temperature-dependent opportunistic pathogen of G.fascicularis. The antagonistic activity between the 100 strains and V. coralliilyticus SCSIO 43001 was tested using a modified Burkholder diffusion assay. Our results showed that V. coralliilyticus SCSIO 43001 inhibits the growth of Erythrobacter flavus and Sphingomonas yabuuchiae. Additionally, we found that three Pseudoalteromonas strains showed moderate to high antibacterial activity against V. coralliilyticus SCSIO 43001 and several other coral-associated Gram-negative bacterial strains.These results suggest that competition between the coral pathogen and other bacteria also occurs in the gastric cavity of coral, and Pseudoalteromonas strains in the gastric cavity of G. fascicularis may provide a protective role in the defense against coinhabiting coral pathogens at elevated temperature.

Identification of bacteria-derived urease in the coral gastric cavity

Nitrogen cycle is critical to maintain a healthy coral reef ecosystem.Urea can provide a source of nitrogen for coral holobiont and is important for coral calcification through degradation by urease.Despite the involvement of coral-associated bacteria in nitrogen fixation,nitrification and denitrification are well recognized,to what extend urea degradation by bacteria contributing to the urea utilization by coral holobiont remains to be investigated.In this study,we demonstrate that the urea utilization is a common feature of Halomonas spp.that is a dominant genus in cultivable coral-associated bacteria.A urease operon was characterized by genome sequencing and gene knock-out technique in Halomonas meridiana SCSIO 43005,isolated from the gastric cavity of healthy scleractinian coral Galaxea fascicularis.H.meridiana showed high urease activity which was induced by urea and deletion of the urease operon reduced the capability to use urea as solo nitrogen source.Furthermore,approximately 1/3 coral-associated bacteria in the IMG/M database possess complete urease operons indicating the involvement of bacteria-derived ureases in coral holobiont.These results suggest that urease from coral-associated bacteria might be important player in the nitrogen cycling of coral reefs.