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[Display omitted] • Environmental heterogeneity affected the genetic structure of coral-algal symbiosis. • Very low amounts of nutrients significantly affect genetic diversity of coral. • In the South China Sea, coral genetic diversity is proportional to phosphate content. • Coral hosts with different genotypes prefer different Symbiodiniaceae types. Global climate change, human activities, and environmental pollution impact coral reefs worldwide. The South China Sea coral reefs have been severely degraded. Genetic diversity among populations of coral is important to implement appropriate protection and restoration measures. Platygyra daedalea , widely distributed in the South China Sea, is stress-resistant and forms a dominant species in some regions. Analyzing the genetic diversity of P. daedalea may provide clues to enhance the resistance of reef-building corals. In this study, we employed one nuclear DNA fragment (ITS) and sixteen microsatellite loci to investigate the genetic diversity of coral host and high-throughput sequencing to investigate on the Symbiodiniaceae types in P. daedalea. (1) The populations of P. daedalea and Symbiodiniaceae types in P. daedalea on Hainan and Xisha Islands were divided into three groups: northern to western Hainan Island, eastern to southern Hainan Island, and Xisha Islands. The ribotypes distribution of coral hosts and the Symbiodiniaceae community composition were strongly correlated with environmental factors in the three areas, especially phosphate concentration and diffuse attenuation. (2) Environmental heterogeneity significantly affected the genetic diversity of coral hosts and diversity of Symbiodiniaceae types, especially nutrient concentration, which significantly affected the diversity of coral-algal symbiosis of P.daedalea even if the seawater nutrient content was within the normal range of coral life. (3) Coral hosts with different genotypes may prefer different Symbiodiniaceae types. This study provides new insights into the changes in the genetic structure and diversity of reef-building corals in the Indo-Pacific region. [ABSTRACT FROM AUTHOR]

Abstract: Hainan''s coast provides favorable climatic, geochemical and biogeographic conditions for the development of extensive coral reefs in China. Observations in five reefs along the NE coast of Hainan showed, however, that the overall density of mobile macrofauna is low and key functional groups such as browsing, scraping or excavating herbivore fish are missing altogether. Coral diseases, partial mortality or tissue degradation are abundant and growth of macroalgal space competitors extensive. Signs of eutrophication, siltation and destructive fishing practices are evident resulting in a strongly altered environment unfavorable for coral recruitment success and survival. Acclimation to the anthropogenically altered conditions in the massive coral Porites lutea occurs at the cost of a decreased photosynthesis: respiration ratio reducing the regenerative capacity of these key framebuilding organisms. Even though, on the organismal level, corals are able to cope with these stressful conditions, a shift is imminent on the ecosystem level from a coral reef to a macroalgae-dominated community if land-based disturbance prevails unabated. [Copyright &y& Elsevier]

Microplastics are emerging contaminants and widespread in the ocean, but their impacts on coral reef ecosystems are poorly understood, and in situ study is still lacking. In the present study, the distribution patterns of microplastics in the environment and inhabiting organisms were investigated along the east coast of Hainan Island, South China Sea, and the physiological impacts of the microplastics on scleractinian corals were analyzed. We documented average microplastic concentrations of 14.90 particles L−1 in seawater, 343.04 particles kg−1 in sediment, 4.97 particles cm−2 in corals, and 0.67–3.12 particles cm−1 in Tridacnidae, Trochidae and fish intestines. Further analysis revealed that the characteristics of microplastics in the organisms were different from those in the environment, indicating preferential enrichment in the organisms. Furthermore, there was an obvious correlation between microplastic concentration and symbiotic density in corals. Furthermore, caspase3 activity was significantly positively correlated with the microplastic content in the small-polyp coral Pocillopora damicornis , but the large-polyp coral Galaxea fascicularis showed higher tolerance to microplastics. Taken together, our results suggest that microplastics are selectively enriched in corals and other reef-dwellers, in which they exact differential stress (apoptotic) effects, with the potential to impact the coral-Symbiodiniaceae symbiosis and alter the coral community structure. ga1 • Microplastics distributed in the environment in the coral reefs around Hainan Island. • Scleractinian corals and other reef-dwellers ingested preferential microplastics. • Caspase3 activity of small-polyp coral was positively affected by microplastic content. • Large-polyp coral showed higher tolerance to microplastics. [ABSTRACT FROM AUTHOR]