Community structure and diversity of nekton in coastal waters of the Pearl River Estuary

【Objective】The purpose of the study was to analyze the nekton community structure and diversity in the coastal waters of the Pearl River Estuary, and to study the ecological status of the species composition, dominant species, resources and spatial and temporal distribution, in order to provide a theoretical basis for the protection and rational development of nekton resources in coastal waters of the Pearl River Estuary. 【Method】A bottom trawl survey was conducted in September 2021(autumn) and April 2022(spring) at 16 stations in the coastal waters of the Pearl River Estuary.Their biodiversity indicators such as relative importance index(IRI), Margalef richness index(D), Shannon-Wiener diversity index(H'), and Pielou evenness index(J') were computed. The methods of tail biomass comparison(ABC) curve, cluster analysis, and non-metric multidimensional scaling(NMDS) analysis were employed to assess spatial and temporal heterogeneity in nekton community structure. 【Result】A total of 215 nekton species were caught in the survey, belonging to 18 orders, 77 families and 48 genera; among them, there were 120 fish species, 91 crustaceans species, and 4 cephalopods species. There were 7 dominant species in the whole year, accounting for 51.81% of the total biomass, and 9 species in autumn and spring, accounting for 70.63% and 63.26% of the total biomass respectively. The dominant species in autumn were Charybdis affinis, Metapenaeus affinis, Parapenaeopsis hungerfordi, Miyakea nepa, Johnius belangerii, Leiognathus brevirostris, Coilia mystus, Nuchequula nuchalis and Plotosus lineatus; and dominant species in spring were C. affinis, M. affinis, C. variegata, P. hungerfordi, M. nepa, J. belangerii, Metapenaeopsis barbata, M.joyneri and Exopalaemon carinicauda. The average richness index D, diversity index H' and evenness index J' were 7.65, 2.56 and 0.66, respectively. The average biomass in autumn and spring were 1510 and 4626 g/h respectively. The W calculated by ABC curve in autumn and spring were-0.062 and-0.049 respectively, indicating that the nekton community in the coastal waters of the Pearl River Estuary was moderately disturbed. The results of cluster analysis and NMDS analysis showed that the communities of nekton in the coastal waters of the Pearl River Estuary were divided into estuarine groups and nearshore groups, and there were extremely significant differences in community structure between the groups(P<0.01). 【Conclusion】The fish species in the coastal waters of the Pearl River Estuary have recovered to a certain extent and the biodiversity level is high, but the traditional dominant economic fishes are gradually replaced by small low-value fishes and crustaceans, and the dominant species are replaced obviously.