Abstract: To reveal the natural food source composition and seasonal dynamics of the feeding habits of Strombus luhuanus in the coral reefs of the Xisha Islands, this study adopted the DNA metabarcoding technology based on the 18S rDNA V4 region to perform high-throughput sequencing on the intestinal contents of this species in summer and autumn, and analyzed the characteristics of its food source species composition and the pattern of seasonal differentiation. The results showed that a total of 241 and 327 operational taxonomic units (OTUs) were obtained from the summer and autumn samples, belonging to 18 phyla, 45 classes, 62 orders, 69 families, 91 genera, 121 species and 17 phyla, 47 classes, 66 orders, 75 families, 101 genera, 132 species, respectively. The number of valid sequences and OTUs in autumn was significantly higher than that in summer. The food sources of S. luhuanus were absolutely dominated by algal groups with Dinophyceae as the core, with the relative abundance of Dinophyceae stably ranging from 55.93% to 57.91% in summer and from 35.95% to 65.09% in autumn. Meanwhile, animal groups such as Arthropoda and Nematoda, as well as fungal groups including Ascomycota and Basidiomycota were detected. Though not the core food sources, these groups reflected the complexity of its feeding habits and the characteristics of detritivory, indicating an overall mixed feeding habit dominated by herbivory and supplemented by detritivory. Significant seasonal differentiation was observed in the food source composition between summer and autumn. S. luhuanus exhibited a specific feeding habit in summer, with benthic attached algae such as Ulvales and Phaeophyceae as the characteristic differential groups; in autumn, the food sources were more diverse, with Dinophyceae such as Prorocentrales and heterotrophic groups associated with organic detritus including Phytomyxea and Ichthyosporea as the dominant characteristic groups, and the food source composition showed higher heterogeneity among different stations. The seasonal differentiation of the feeding habits of S. luhuanus is an adaptive strategy to the seasonal fluctuations of resources in the coral reef ecosystem. This species functions in both the utilization of benthic algae and the decomposition of organic detritus during feeding, serving as an important primary consumer and detritivore in the coral reef ecosystem. This study provides the first molecular empirical evidence for the natural food source composition of S. luhuanus in the Xisha Islands, and the results offer a scientific basis for the evaluation of the ecological functions of this species, the protection of coral reef resources, and the formulation of bait ratios for its artificial culture.

Key words: Strombus luhuanus, DNA metabarcoding, 18S rDNA V4 region, dietary composition, seasonal dynamics