Abstract:

Aims: This study aimed to investigate fish diversity and community characteristics in estuarine reef waters and to examine seasonal differences in fish species composition, community structure, and functional characteristics in waters adjacent to Wanshan Island in the Pearl River Estuary. 

Methods: Fish assemblages were surveyed using trammel nets in March 2021 (spring) and September 2021 (autumn). Species composition, community structure, biodiversity, and seasonal differences in fish assemblages in waters adjacent to Wanshan Island were analysed. 

Results: A total of 97 fish species were recorded, including 59 species in spring and 60 species in autumn. The species-level Jaccard similarity index between the two seasons was 0.23, indicating low similarity in species composition. In contrast, the Margalef richness index, Shannon-Wiener diversity index, Pielou evenness index, average taxonomic distinctness (Δ+), and variation taxonomic distinctness (Λ+) were similar between seasons, with absolute differences of 0.003, 0.003, 0.004, 0.71, and 1.60, respectively. Functional β-diversity was dominated by the turnover component rather than the nestedness-resultant component, indicating that seasonal functional differences arose primarily from the replacement of portions of functional trait space rather than from the functional space of one season being nested within that of the other. Functional richness (FRic), functional evenness (FEve), functional divergence (FDiv), and functional dispersion (FDis) were all higher in spring than in autumn. Migratory fishes contributed greater proportions of total numerical abundance and biomass in spring, while medium- and large-bodied fishes also accounted for higher proportions of numerical abundance and biomass. Moreover, the trophic-level distribution was broader and multimodal in spring, indicating a broader trophic structure and a wider range of potential resource-use strategies. 

Conclusions: Fish species composition differed markedly between spring and autumn, whereas conventional diversity and taxonomic distinctness indices remained broadly similar. Seasonal functional differences were mainly driven by turnover in functional trait space, and the spring assemblage exhibited broader functional and trophic distributions than the autumn assemblage. These findings provide baseline information and a scientific basis for fish diversity conservation and the sustainable use of fishery resources in reef waters of the Pearl River Estuary.

Key words: Pearl River Estuary, reef fishes, community structure, functional diversity