Abstract: Psammocora contigua is one of the representative reef-building corals in the waters around Wuzhizhou Island. However, molecular responses of such non-dominant coral species under relatively high-turbidity marine conditions remain poorly understood. To reveal its transcriptomic differentiation and explore the potential association with biomineralization-related basic processes, P. contigua samples were collected at a depth of 8m from the southern and northern sides of Wuzhizhou Island, Sanya, Hainan. Combined with in situ seawater environmental monitoring and transcriptome sequencing, the expression characteristics of the coral and its symbiotic algae under different marine environmental conditions were analyzed. The results showed significant differences in seawater temperature, salinity, turbidity, and dissolved oxygen between the southern and northern sides of Wuzhizhou Island, with turbidity significantly higher on the northern side than on the southern side. Correspondingly, coral samples from the northern side showed higher transcriptomic similarity, whereas those from the southern side exhibited greater transcriptomic heterogeneity and a higher proportion of specifically expressed transcripts. Differentially expressed genes in corals were mainly associated with stress response, transmembrane transport, cytoskeleton regulation, ATP(adenosine triphosphate) metabolism, and ion transport. In contrast, the symbiotic algal transcriptome showed no obvious expression differentiation trend, with fewer differentially expressed genes and a lower overall response amplitude than corals, although changes were still observed in functional categories such as basic metabolism, membrane transport, protein homeostasis, and intracellular transport. These results indicate that, under the environmental heterogeneity characterized by turbidity differences around Wuzhizhou Island, P. contigua exhibited relatively clear transcriptomic differentiation, whereas its symbiotic algae maintained a relatively conserved expression state. Meanwhile, expression changes related to ion transport, energy metabolism, and cytoskeleton regulation suggest a potential link between environmental responses and biomineralization-related basic processes in corals. Although limited by sample size, this study enriches transcriptomic data for non-dominant reef-building corals around Wuzhizhou Island, provides molecular references for tropical coral reef conservation, restoration, and ecological assessment, and lays a data foundation for further verification of the relationship between environmental responses and biomineralization.

Key words: Psammocora contigua, transcriptome, turbidity, environmental response, biomineralization