Spring-time nektonic invertebrate assemblages of and adjacent to the Yangtze Estuary

Abstract

Identifying drivers of coastal nektonic invertebrate community structure requires detailed analyses of species assemblage composition and environmental variables. We analyze biological and environmental data collected over five spring seasons from 2013 to 2017 from waters in and adjacent to the Yangtze Estuary. Of 31 species, crustaceans were dominant in abundance and biomass. Abundance and biomass had different spatial distribution characteristics among years. The Taiwan Warm Current, low in dissolved oxygen (DO) and high in temperature (T), encroached into the East China Sea from Taiwan Strait, contributing to hypoxic conditions and warm waters. Yangtze River flows contributed to low estuarine salinity (S). Canonical correlation analysis (CCA) and analysis of similarities (ANOSIM) identified that nektonic invertebrate community structure fluctuated among five years and had significant spatial variation, of which communities of 2013, 2014 and 2015 differed significantly from all other years and no significant difference was apparent between that of 2016 and 2017, and two distinct assemblages were stratified by depth (D). Nekton abundance and biomass were highest in 2014, and varied significantly over time. D, DO, T and S were key factors structuring the nektonic invertebrate community. D significantly affected the spatial distribution of communities, while T significantly affected temporal variation. Hypoxic zones were associated with low abundance and biomass, indicating DO also strongly influenced community structure and species growth.