Fish Community Diversity In Haizhou Bay And Its Relationship With Environmental Factors

Haizhou Bay is a typical open area in southern Yellow Sea. The shelf decreasesfrom west to east and had muddy and sandy sediment. Three main currents, i.e. LunanCoastal Current, Subei Coastal Current and Yellow Sea Warm Current, have majorinfluences on this region. Seasonal variation of Yellow Sea Cold Water Mass also hassignificant effect on physicochemical environment in Haizhou Bay. This bay is one ofthe important spawning and nursery grounds for many important commercial fishspecies such as Trichiurus lepturus, Larimichthys polyactis and Scomberomorusniphonius. Over the past several decades, intensive fishing pressure had significanteffects on the fishery resources and dominant fish species have changed from thelarge, higher trophic level species to small, lower trophic level species.Knowledge of spatio-temporal patterns of fish diversity is critical to preservinghot-spots of biodiversity, habitats for important fish species, and understandingfunctional characteristics of ecosystem. Spatio--temporal patterns of fish diversity inHaizhou Bay and its relationship with environmental factors were evaluated usingdata collected from five comprehensive surveys of the bay between March-December,2011. It is important to provide theoretical basis for fisheries rescores managementand utilization. The results were as follow:A total of96fish species were collected in these surveys, which belonging to2classes,15orders,51families and79geniuses, including90actinopterygii speciesand6elasmobranch species. Perciformes, Scorpaeniformes, Pleuronectiformes andClupeiformes were the species-richest, accounted for47.78%,14.44%,11.11%and10.00%, respectively. Aulopiformes, Gadiformes, Lophiiformes and Osmeriformeshad only one species, respectively. Rajiformes was species-richest,4species inelasmobranch. Carcharhiniformes and Hexanchiformes had only one species, Sphyrnazygaena and Squatina japonica, respectively.Generalized additive model (GAM) was applied to analyze the relationship between taxonomic distinctness of fishes and environmental factors. Results showedthat taxonomic distinctness indices presented obvious seasonal variations, beinghighest in March and lowest in July. Spatial variations of taxonomic distinctnessindices were also obvious, which were related to spatial difference of environmentalfactors in Haizhou Bay. GAM showed that water depth and bottom dissolved oxygenhad a significant effect on average taxonomic distinctness (Δ+) of fishes, while waterdepth, bottom water temperature and bottom dissolved oxygen were the mostimportant environmental factors influencing variation in taxonomic distinctness (Λ+)of fishes in Haizhou Bay. We also found that taxonomic distinctness indices decreasedfrom north to south sea areas located in different latitude of China, suggesting thatlatitude variation had an important influence on taxonomic distinctness for fishes.Fish community diversity in Haizhou Bay presented obvious seasonal variations,being highest in summer and autumn, and lowest in winter. Temporal trends would bebest explained by the seasonal migration of migratory fishes in Haizhou Bay. Theresults also indicated that30m isobaths was an important biology boundary,suggesting that spatial patterns of fish diversity might be associated with complexbottom topography and spatial variations of water mass and currents. GAMs showedthat depth and bottom water temperature had significant effect on fish communitydiversity, suggesting that environmental gradients might play important roles inaffecting the spatial distribution of fish community diversity.PCA was carried out to distinguish diversity components. The results showedthat the11diversity indices were grouped into four components:(1) species numbersand richness,(2) heterogeneous indices,(3) evenness, and (4) taxonomic relatedness(Δ+and Λ+).PCA was also applied to divided dominant fish species in Haizhou Bay into threegroups: high trophic level and demsersal fishes; medium trophic level and demsersalfishes; medium trophic level and pelagic fishes. In addition, PCA was also used toconcentrate the variance of original fish species data into PCs, which could beconsidered as indicators to evaluate diversity variation with environmental changes.The results showed that PCs were strongly influenced by environmental factors (i.e. water temperature, salinity and depth) which could change physiology characteristicsof fishes.GAMs were applied to analysis the relationship between fish communitydiversity in different taxonomic levels and environmental factors. The results showedthat depth, bottom temperature, chlorophyll A and month had significant effect on fishcommunity diversity in different taxonomic levels. However, bottom pH was the mostimportant environmental factor influencing fish community diversity in family andgenus levels. These results indicated that fish community diversity in differenttaxonomic levels had different environmental effect.