Estimating spatial response distances of reef-associated communities in the Wuzhizhou Island marine ranch using generalized additive models

Artificial reefs are widely used to enhance fishery resources and restore degraded marine habitats, yet quantitative information on the spatial responses of biological communities to reef distance remains limited in tropical marine ranching systems. This study investigated the spatial response distances of different catch groups to reef distance in the Wuzhizhou Island marine ranch, Sanya, Hainan Province, China. Based on five surveys conducted at 28 stations from 2019 to 2021, a total of 263 species of catches were collected using five sampling methods angling, gill net, trap, diving sampling, and bottom trawling. The catches were classified into five groups total catches, reef-dependent, reef-approaching, sand-mud bottom-preference, and strong-swimming. Generalized additive models (GAMs) were fitted using the Shannon-Wiener diversity ( H ), Pielou evenness ( J ), Margalef richness ( d ), and the Index of Relative Importance ( IRI ) as response variables. GAMs were used to characterize the relationships between community indices and reef distance, with additional sampling-method-adjusted models conducted to evaluate sensitivity to sampling heterogeneity. The strong-swimming group the reef-distance smooths were nonsignificant for all indices examined; no transition response distance was reported. The estimated response distances spanned 830–1120 m for the total catches group, 1420–1560 m for the reef-approaching group, and 1100–1450 m for the sand-mud bottom-preference group, whereas a single transition response distance of 890 m was identified for the reef-dependent group. These results demonstrate group-specific spatial responses to reef distance and provide quantitative reference information for spatial assessment and differentiated management of tropical marine ranching systems.