The diversity and biogeography of macrobenthic fauna in the rocky intertidal zone of islands in the Pearl River estuary: effects of island area, isolation, salinity and human disturbance

The theory of classical island biogeography alone cannot encapsulate the dynamic pattern of island biodiversity, factors such as salinity, and anthropogenic influence and species traits should be considered. Here, islands of varying sizes, degrees of isolation, salinity, and anthropogenic influence from the inner to the outer waters of the Pearl River estuary in China, were selected as the sampling sites. During January to March 2023 (dry season), macrobenthic fauna, comprising various groups with distinct ecological traits, were collected in the rocky intertidal zones. Environmental gradients were derived from long-term salinity, temperature, depth, and dissolved oxygen (DO) records from the Pearl River Estuary ecosystem field station, field measurements of anthropogenic disturbance, and GIS-calculated isolation distances. Island areas were obtained from the Guangdong Province Department of Natural Resources. The findings revealed that the species richness of the total, Molluscs and Annelids fit the power-function species–area relationship, whereas Arthropods did not. The generalized linear models showed a significant negative correlation between anthropogenic disturbances and Arthropod richness. Principal coordination analysis and beta diversity indicated substantial dissimilarities in the spatial structure similarity of communities among islands in this area. The analysis of generalized dissimilarity modeling indicated both environmental gradients and spatial distance could affect the β diversity of macrobenthic fauna. In the upper tidal zone, β diversity was predominantly influenced by geographic distance, while in the middle and lower zones, community composition was shaped by the salinity gradient. The outcomes of this study supports the role of area and spatial isolation in structuring community composition and diversity. However, environmental gradients such as salinity and anthropogenic disturbances may take precedence over other biogeographical processes. The significance of these gradients varies across different groups.