Taxonomic diversity of fish assemblages in the Changjiang Estuary and its adjacent waters

Taxonomic diversity of fish assemblages in the Changjiang Estuary (Yangtze River Estuary) and its adjacent waters was analyzed based on bottom trawl surveys carried out by R/V Beidou in June, August and October 2006. Four groups of fishes were identified for each survey by the twoway indicator species analysis (TWIA). Taxonomic distinctness, species richness and phylogenetic diversity were used to detect changes in taxonomic structure of fish assemblages. Most dominant fish species mainly belonged to Perciformes, Pleuronectiformes, Clupeiformes, Scorpaeniformes and Tetraodontiformes. Species richness in offshore waters of the survey area was higher than that in the other area. The average taxonomic distinctness value (AvTD, △⁺) of each fish assemblage was close to the average taxonomic distinctness of master list in the Changjiang Estuary (79.9), and had a positive correlation with species richness and Shannon diversity index (H'). A negative correlation was found between variations in taxonomic distinctness (VarTD, Λ⁺) and traditional diversity indices, which were caused by fish species component that led to longer average path lengths among species. Taxonomic diversity index (△) had the similar results with species richness, H', Simpson diversity index (D) and Pielou's evenness index (J'). VarTD also kept stable, which further certificated that fish assemblages and ecological environment were in equilibrium. Taxonomic distinctness index (△^*) was relatively stable in most of fish assemblages, and had higher values in some fish assemblages for a few absolutely dominant species. The present study showed that fish community formed new equilibrium stability in 2006 in the Changjiang Estuary when compared with those in the corresponding months of annual survey from 1985 to 1986. And AvTD in each sampling station was lower than AvTD of master list in the Changjiang Estuary, so some ecological niches were absent in each sampling stations from taxonomic or phylogenetic relationships, these would be helpful to stock natural resource and maintain ecological equilibruim of fish assemblages.