Coral reefs are continuing to decline worldwide due to anthropogenic climate change. The study of the molecular diversity and biogeographical patterns of Symbiodiniaceae, is essential to understand the adaptive potential and resilience of coral–algal symbiosis. Next generation sequencing was used to analyze the Symbiodiniaceae rDNA internal transcribed spacer 2 marker genes from 178 reef-building coral samples in eight coral habitats across approximately 13° of latitude in the South China Sea (SCS). A total of three Symbiodiniaceae genera, Cladocopium , Durusdinium , and Gerakladium , as well as 31 dominant Symbiodiniaceae types, were identified. Symbiodiniaceae richness, diversity, and community composition varied according to latitude; intermediate and low latitude coral reefs (IR and LR) have higher Symbiodiniaceae richness and diversity than high latitude coral habitats (HC and HR). A PERMANOVA analysis found significant differences in the Symbiodiniaceae community composition in the SCS ( F = 14.75, R 2 = 0.20, p = 0.001 < 0.01). The major dominant Symbiodiniaceae types were C1 in the HC and the HR, C1/Cspc/C50/C15 and D1 in the IR, and C3u and C15 in the LR. Canonical correspondence analysis showed that the relative abundance of different Symbiodiniaceae types is affected by multiple environmental factors. Phylogenetic analysis indicated that the Symbiodiniaceae type Cladocopium , which shared common ancestors, shows similar environmental adaptability. Based on these results, we suggest that coral host species played a relatively small role in the identity of the dominant Symbiodiniaceae type. Therefore, the biogeographical patterns of Symbiodiniaceae may be mainly affected by environmental factors. Our research provides a comprehensive overview of the biogeography of Symbiodiniaceae in the SCS, where coral communities and reefs are widely distributed across different latitude regions and have variable environmental conditions. Our data will provide support for further study of the regional diversification of Symbiodiniaceae and the ecological resilience of the coral-Symbiodiniaceae symbioses.

Grouper iridovirus (GIV) is one of the most serious pathogens in mariculture and causes high mortality rates in cultured groupers; then, effective medicines for controlling GIV infections are urgently needed. Viola philippica is a well‐known medicinal plant, and the application of V. philippica aqueous extracts against GIV infection was assessed by different methods in this study. The results showed that the working concentration of V. philippica aqueous extracts was 10 mg/ml. V. philippica aqueous extracts below 10 mg/ml have no significant cytotoxic effects on cell viability, while extracts over 15 mg/ml decreased cell viability and showed cytotoxic activity. V. philippica aqueous extracts had excellent inhibitory effects against GIV infection in vitro and in vivo. The possible antiviral mechanism of V. philippica was further analysed, which indicated that V. philippica did no damages to GIV particles, but it could disturb GIV binding, entry and replication in host cells. V. philippica had the best inhibitory effects against GIV during viral infection stage of binding and replication in host cells. Overall, the results suggest that appropriate concentration of V. philippica aqueous extracts has great antiviral effects, making it an interesting candidate for developing effective medicines for preventing and controlling GIV infection in farmed groupers.

Vibrio alginolyticus (V. alginolyticus) is a major opportunistic pathogen to both marine animals and humans, which has also caused heavy economic losses to mariculture. The aim of this study was to develop highly specific aptamers for V. alginolyticus. Single‐stranded DNA (ssDNA) aptamers with high binding affinity to viable V. alginolyticus were generated by Systematic Evolution of Ligands by Exponential Enrichment (SELEX) and identified by flow cytometric analysis in this study. The selected aptamers showed high specificity for V. alginolyticus and low apparent binding for other bacteria. The aptamers formed distinct stem‐loop structures, which could form the basis of aptamers’ specific binding to the target V. alginolyticus. Aptamer VA2 and VA8 showed particularly high binding affinity constant (Kd) of 14.31 ± 4.26 and 90.00 ± 13.51 nM, respectively. The aptamers produced no cytotoxic effects in vitro and in vivo. ssDNA aptamers were successfully selected against the viable bacteria pathogen V. alginolyticus by SELEX. The aptamers selected in this study could be not only applied as specific chemical molecular probes for studying V. alginolyticus pathogenesis to Trachinotus ovatus, but also developing rapid convenient diagnosis assay for V. alginolyticus infection, even when applied to the complex sample matrix, such as food and environment samples.

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