Spatial variation of demersal fish diversity and distribution in the East China Sea: Impact of the bottom branches of the Kuroshio Current

The bottom branches of the Kuroshio Current in the East China Sea were recently discovered from physical and chemical oceanographic perspectives. To examine the diversity and distribution of demersal fish community in the East China Sea and to assess the impact of the bottom branches of the Kuroshio Current, we investigated the demersal fish community with an Agassiz trawl in the East China Sea shelf in the summer of 2015. A total of 72 species were collected in 40 sampling sites with Amblychaeturichthys hexanema, Champsodon snyderi, Odontamblyopus rubicundus, Cynoglossus interruptus, and Coelorinchus multispinulosus being the top 5 most abundant species. Three ecological groups of demersal fish-the Coastal group (CG), Transitional group (TG) and Kuroshio group (KG) were identified through multivariate analyses, and significant differences in species composition among the three ecological groups were detected. The dominant species varied among the groups: gobies in CG; Neobythites sivicola, Cynoglossus interruptus and Aseraggodes kobensis in TG; and Champsodon snyderi, Callionymus beniteguri and Ostorhinchus fasciatus in KG. Most diversity indices, including the number of species (S), Margalef's index (d), Shannon-Wiener's index (H'(log(2))), Simpson's index (1-lambda'), rarefaction index (ES(100)), Hill's number (N-infinity), average taxonomic diversity (Delta), total taxonomic distinctness (S Delta(+)), variation in taxonomic distinctness (Lambda(+)) and total phylo-genetic diversity (S Phi(+)) increased from inshore to offshore, whereas abundance and biomass increased from south to north. K-dominance curves suggested diversity rankings of offshore region > inshore region and southern region > northern region for regional comparisons. A diversity ranking of KG > TG > CG for group comparisons was also detected. The funnel and ellipse plots of taxonomic measures indicated that diversity was approximately equal to the expected range in KG (healthy), whereas it was significantly lower in CG (unhealthy). CCA (canonical correspondence analysis) revealed that turbidity, fine silt sediment, fluorescence, dissolved oxygen and salinity were the most active environmental variables influencing demersal fish community. RDA (redundancy analysis) found turbidity and temperature showed significant associations with the biodiversity matrix.