Sea turtles are renowned "living fossils" and ideal flagship marine conservation species. Sea turtles exhibit strong fidelity to their nesting grounds, and the quality of nesting grounds is closely linked to their survival. Microbial diversity, abundance, and potential pathogens are important indicators for measuring 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 was conducted at the nesting grounds of green turtles on the North Island in the Xisha Islands. We compared and analyzed the bacterial community composition and characteristics of the sand of nests before and after hatching and the samples of hatched eggshells, unhatched egg contents, and gastrointestinal tracts of deceased hatchlings using high-throughput Illumina sequencing technology. The results showed that the bacterial community composition in the sand of nests before and after hatching was significantly different (R = 0.941, P = 0.001). The sand of nests before hatching showed higher bacterial diversity and richness than that after hatching (P < 0.001). Additionally, significant differences in the bacterial community composition between hatched eggshells, unhatched egg contents, and gastrointestinal tracts of deceased hatchlings were observed (R = 0.438, P = 0.001); the bacterial diversity and richness of the hatched eggshells were significantly higher than those of the latter two (P < 0.001). The relative abundance of  unclassified_d__Bacteria, Bacillus, Streptomyces, and others in the sand of nests after hatching was significantly decreased than that in the sand of nests before hatching (P < 0.05); however, the relative abundance of Flavobacterium, Brevundimonas, Acinetobacter, and others 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 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.
 

microbial diversity, pathogen, green turtle, nesting ground