Dietary ecological characteristics of 10 sympatric parrotfish species revealed by DNA metabarcoding: A case study in the Qilianyu Islands, Xisha Islands

Parrotfish are a key functional group in coral reef ecosystems, and their feeding behavior directly regulates the coral–algae competition balance and drives bioerosion processes. In this study, we aimed to elucidate the algal control mechanisms and sympatric coexistence strategies of parrotfish on coral reefs by resolving their detailed dietary composition. We analyzed 10 co-occurring parrotfish species from the Qilianyu Islands, Xisha Islands, using 18S and 16S rRNA high-throughput sequencing for DNA metabarcoding of intestinal contents, combined with complex network analysis to systematically examine dietary composition, trophic niche differentiation, and food web structure. The results showed that: (1) parrotfish have a broad dietary spectrum covering eukaryotic algae, prokaryotic algae, and benthic invertebrates; (2) significant dietary differentiation exists among functional groups, with Browser preferring coralline algae (21.30%), Excavator favoring microalgae (21.40%), and Scraper mainly consuming surface filamentous algae (18.28%); this differentiation alleviates interspecific competition through fine-scale resource partitioning; (3) the parrotfish–prey network exhibits significant modularity, with Phaeophyta, Chlorophyta, Platyhelminthes, Pyrrophyta, and Synechococcales (Cyanobacteria) serving as key nodes maintaining network stability. This study demonstrates that multi-level dietary differentiation is the core mechanism enabling sympatric coexistence of the 10 parrotfish species, and that complementary feeding strategies among functional groups facilitate comprehensive coverage of diverse algal types. These findings provide important scientific bases for the conservation and restoration of coral reef ecosystems.