Community structure and disturbance status of intertidal macrobenthos in Nanpeng Archipelago

The investigation of macrobenthic communities in the intertidal zone of the Nanpeng Archipelago off the coast of Yangjiang City, Guangdong Province, has not yet been carried out. The characteristics of its community structure and the degree of anthropogenic disturbance remain unclear, resulting in a lack of critical supporting data for ecological status assessment. To elucidate the structural characteristics of the benthic community and evaluate its disturbance level, we set 12 transects on Nanpeng Dao, Dahuo Dao, Erhuo Dao, Huzai Dao and Huangchengshan Dao in August 2025, and carried out the first systematic survey of intertidal macrobenthos. A total of 45 macrobenthic species were identified, belonging to 8 phyla and 30 families, with Mollusca and Arthropoda as the dominant groups. The overall mean abundance was 586 ind·m⁻² and the mean biomass was 590.46 g·m⁻². The communities exhibited a vertical distribution pattern: higher density in the high intertidal zone and greater biomass in the low intertidal zone. Bray-Curtis clustering and non-metric multidimensional scaling (NMDS) analyses classified the 12 transects into three subgroups: sheltered rocky habitat, exposed rocky habitat and sandy habitat. SIMPER analysis revealed that the community differences among islands were mainly contributed by dominant species including Planaxis sulcatus, Nodilittorina radiata, N. trochoides, Tetraclita japonica and Chthamalus malayensis. Based on the ecological habits of dominant species, macrobenthos in the survey area were divided into three functional groups: sessile filter-feeders, attached grazers and shallow-burrowing filter-feeders. These groups predominated in sheltered rocky, exposed rocky and sandy habitats, respectively. Combined analyses of abundance-biomass comparison (ABC) curves and taxonomic distinctness indices indicated that the macrobenthic communities of Nanpeng Dao and Dahuo Dao were slightly disturbed, while those of Erhuo Dao, Huzai Dao and Huangchengshan Dao were undisturbed. The overall taxonomic distinctness indices were Δ⁺ = 66.65 and Λ⁺ = 493.75, both falling within the 95% confidence interval. Only Δ⁺ of Dahuo Dao was below the theoretical lower limit, indicating its simplified phylogenetic hierarchy and significant impacts from human activities. In conclusion, the overall ecological status of intertidal macrobenthic communities in the Nanpeng Archipelago is favorable, while disturbance levels differ significantly among different islands.