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Outbreaks of crown-of-thorn starfish (COTS) have caused dramatic declines in reefs through predation on corals, but the post-bloom effects of COTS may still potentially threaten the environment and living organisms due to massive organic decomposition. This stimulation experiment showed that the decomposition of COTS debris triggered an extra mineralization process and resulted in acidifying, hypoxic, and eutrophic seawater. Consequently, the photosynthetic efficiency of coral symbionts decreased by 83%, and coral bleached after removing the stress within two days, then the coral skeleton dissolved at rates of 0.02–0.05 mg cm−2 day−1. Within two weeks, the photosynthesis and growth of benthic algae were suppressed by 27–86% and 1.5–16%, respectively. The mortality of turf algae and coralline algae indicated compromised primary productivity and limited coral recruitment, respectively. However, macroalgae, as coral competitors, became the only survivors, with increasing chlorophyll content. This study suggests a continuing decline of reefs during the collapse phase of COTS outbreaks and highlights the need for improving control strategies for the COTS population. [ABSTRACT FROM AUTHOR]

Global climate change has resulted in large-scale coral reef decline worldwide, for which the ocean warming has paid more attention. Coral is a typical mutually beneficial symbiotic organism with diverse symbiotic microorganisms, which maintain the stability of physiological functions. This study compared the responses of symbiotic microorganisms and host metabolism in a common coral species, Pavona minuta, under indoor simulated thermal and cold temperatures. The results showed that abnormal temperature stresses had unfavorable impact on the phenotypes of corals, resulting in bleaching and color change. The compositions of symbiotic bacteria and dinoflagellate communities only presented tiny changes under temperature stresses. However, some rare symbiotic members have been showed to be significantly influenced by water temperatures. Finally, by using ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS) method, we found that different temperature stresses had very different impacts on the metabolism of coral holobiont. The thermal and cold stresses induced the decrease of anti-oxidation metabolites, several monogalactosyldiacylglycerols (MGDGs), and the increase of lipotoxic metabolite, 10-oxo-nonadecanoic acid, in the coral holobiont, respectively. Our study indicated the response patterns of symbiotic microorganisms and host metabolism in coral to the thermal and cold stresses, providing theoretical data for the adaptation and evolution of coral to a different climate in the future. [ABSTRACT FROM AUTHOR]

Ciguatera poisoning is mainly caused by the consumption of reef fish that have accumulated ciguatoxins (CTXs) produced by the benthic dinoflagellates Gambierdiscus and Fukuyoa. China has a long history of problems with ciguatera, but research on ciguatera causative organisms is very limited, especially in the Beibu Gulf, where coral reefs have been degraded significantly and CTXs in reef fish have exceeded food safety guidelines. Here, five strains of Gambierdiscus spp. were collected from Weizhou Island, a ciguatera hotspot in the Beibu Gulf, and identified by light and scanning electron microscopy and phylogenetic analyses based on large and small subunit rDNA sequences. Strains showed typical morphological characteristics of Gambierdiscus caribaeus, exhibiting a smooth thecal surface, rectangular-shaped 2′, almost symmetric 4″, and a large and broad posterior intercalary plate. They clustered in the phylogenetic tree with G. caribaeus from other locations. Therefore, these five strains belonged to G. caribaeus, a globally distributed Gambierdiscus species. Toxicity was determined through the mouse neuroblastoma assay and ranged from 0 to 5.40 fg CTX3C eq cell−1. The low level of toxicity of G. caribaeus in Weizhou Island, with CTX-contaminated fish above the regulatory level in the previous study, suggests that the long-term presence of low toxicity G. caribaeus might lead to the bioaccumulation of CTXs in fish, which can reach dangerous CTX levels. Alternatively, other highly-toxic, non-sampled strains could be present in these waters. This is the first report on toxic Gambierdiscus from the Beibu Gulf and Chinese waters and will provide a basis for further research determining effective strategies for ciguatera management in the area. [ABSTRACT FROM AUTHOR]

Global warming and sea-level rise (SLR) induced by rising atmospheric CO2 concentrations can cause coral bleaching, death, and submergence of the world's coral reefs. Adopting the GIS and RS methods, we modeled how these two stressors combine to influence the future growth of the atolls and table reefs of three archipelagoes in the South China Sea (SCS), based on geomorphic and ecological zones. A large-scale survey of the coral communities in Xisha Islands in 2014, Dongsha Islands in 2014–2016 and Nansha Islands in 2007 provided zone-specific process datasets on the range of reef accretion rates. Sea surface temperature and extreme (minimum and maximum) SLR data above 1985–2005 levels by 2100 in the SCS were derived from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) models forced with the Representative Concentration Pathways (RCPs). Our model projected that: (1) the Xisha Islands and Dongsha Islands may have a better growth status, because the reef flat biotic sparse zone may be recolonized with hard coral and become a biotic dense zone; (2) the southern Nansha Islands reefs have a risk of stopping growing due to their earlier annual bleaching years. The increasing of water depths of these reefs is stronger in the RCP with more emissions. Our approach offers insights into the best-case and worst-case impacts of two global environmental pressures on potential future reef growth under a changing climate. [ABSTRACT FROM AUTHOR]