Habitat Heterogeneity Drives Intertidal Macrobenthic Community Differentiation via Environmental Filtering, Species Turnover, and Ecological Network Reorganization

Intertidal habitat heterogeneity can shape macrobenthic communities, but its links to assembly processes and network stability remain uncertain. Macrobenthos were surveyed at 22 sites across muddy sediment (MA), oyster farming (OF), eastern rocky reef (EA), and southern rocky reef (SA) habitats around Nan’ao Island. Habitat type explained 25.5% of compositional variation, whereas observed richness and evenness showed no consistent among habitat differences. Mean between-habitat Bray-Curtis dissimilarity (0.730) and turnover (0.623) exceeded their within-habitat values (0.634 and 0.555), indicating that species replacement, rather than nested species loss, dominated community differentiation. Functional richness differed among habitats, whereas most other functional indices remained comparatively stable. Neutral-model fits were stronger in EA and SA (R2 = 0.501 and 0.475, respectively) than in MA and OF, and null-model partitioning indicated undominated processes in MA and OF but greater homogenizing dispersal in rocky habitats. SA contained the largest co-occurrence network (24 nodes, 81 edges), although robustness was highest in OF. Exploratory PLS-SEM showed positive associations between habitat heterogeneity and environmental filtering (β = 0.591, p = 0.004) and between turnover and potential network stability (β = 0.593, p = 0.022), whereas the assembly–stability association was nonsignificant (β = 0.044, p = 0.856). These cross-sectional associations support a conceptual pathway linking habitat-related environmental gradients, species turnover, assembly shifts, and network reorganization.