Abstract
Habitat heterogeneity and human disturbances drive variations in interspecific interactions among fish species. Trophic niche analysis is a crucial approach for understanding these interactions. This study investigates the interspecific interaction mechanisms of two scorpionfish species, Sebastiscus marmoratus and Scorpaenopsis cirrosa, across different habitat conditions in the Wanshan Archipelago of the Pearl River Estuary. Three island groups-Guishan Island, Wailingding Island, and Dongao & Wanshan Islands-were selected as study sites. Using carbon and nitrogen stable isotope analysis, we examined variations in their trophic relationships. The results revealed significant regional differences in the δ(13)C values of S. marmoratus and S. cirrosa (p < 0.05), indicating regional variation in their food sources. Bayesian mixing model analysis showed that at Guishan Island, annelids constituted the primary food source for both species. However, at Wailingding Island and Dongao & Wanshan Islands, their reliance on annelids significantly decreased, with a preference shift towards mollusks, reflecting region-specific foraging strategies and niche differentiation. The δ(15)N values of the two species did not exhibit significant regional differences, suggesting that S. marmoratus and S. cirrosa occupy similar trophic levels across different regions. Trophic niche metrics, including CR, NR, CD, and TA, indicated that S. cirrosa has a broader trophic niche, suggesting a more flexible feeding strategy and a potential competitive advantage in resource utilization. The two species exhibited overlapping trophic niches, with distinct regional variations. Notably, at Guishan Island, where trophic niches were the broadest, potential competition between the species was most pronounced, which may be associated with higher human activity intensity. Differences in ecosystem structure among islands contributed to variations in food resource availability and niche space, ultimately shaping the foraging behaviors and adaptive strategies of S. marmoratus and S. cirrosa across regions. These findings provide theoretical insights into interspecific interactions in heterogeneous habitats and inform fisheries resource conservation.