Microbial diversity characteristics and differential analysis in green turtle nests in the Xisha Islands, South China...

Sea turtles are renowned "living fossils" and ideal flagship marine conservation species. Sea turtles display high fidelity to their nesting grounds, and the quality of nesting grounds is related to the survival of sea turtles, in which microbial diversity, abundance, and potential pathogens are important indicators for assessing the quality of nesting grounds. The Xisha Islands are the largest nesting grounds for green turtles (Chelonia mydas) in China. Protecting the security and sustainability of the nesting grounds is of significant importance. This study compared and analyzed the bacterial community composition and characteristics of the nests of green turtles using high-throughput Illumina sequencing technology. The results showed that the sand of nests before hatching showed higher bacterial diversity and richness than that after hatching (P < 0.001). Additionally, the bacterial diversity and richness of the hatched eggshells were significantly higher than those of unhatched egg contents and the gastrointestinal tracts of deceased hatchlings (P < 0.001). The relative abundance of Bacillus, Streptomyces in the sand of nests after hatching was significantly decreased compared to that in the sand of nests before hatching (P < 0.05); however, the relative abundance of Flavobacterium, Brevundimonas, Acinetobacter increased significantly (P < 0.001). Most of the bacteria identified in our study are opportunistic pathogens that cause infections in plants and animals. The unhatched egg contents had a larger amount of opportunistic pathogens than hatched eggshells and the gastrointestinal tracts of deceased hatchlings. The presence and long-term accumulation of these pathogens may disrupt the ecological balance of the microbial community in nesting grounds, increase the susceptibility of sea turtle eggs, and pose a threat to the hatching and hatchling survival of sea turtle eggs, thereby posing a certain level of safety risk. The outcomes of this study could offer scientific support for the management and restoration of the nesting grounds in the Xisha Islands.IMPORTANCEMany studies have shown that microorganisms influence the reproduction and hatching of sea turtles. The quality of nesting grounds is critically important for the successful reproduction of sea turtles, determining success in egg laying and influencing factors that affect the health of sea turtle populations. The Xisha Islands are the largest nesting grounds for green turtles in China. Regular and preventive monitoring of the microbial community composition in the sand and nests of nesting sites can contribute to the management and conservation of the nests.