Relationship Of Crustaceans Community Structure And Resources Distribution With Environment Factors In The Jiaojiang Estuary

Based on the data from two oceanographic surveys in the Jiaojiang River estuaryduring April and October2010, the spatial and seasonal variations in speciescomposition, dominant species, species diversity and communities of shrimps, and torelate these patterns to environmental variation in April and October2010. Theinfluences of dominant species，water temperature，salinity, and depth on thedistribution and abundance of crustaceans were evaluated.The major results indicated that:（1）A total of16species of shrimp were found in our investigations, whichbelonged to12families under8genera.14species of shrimp were found inspring(April)and12species in autumn(October).Index of relative importance(IRI)wasemployed to determine the importance of species, in spring,6dominant species wereidentifiedincluding Acetes chinensis, Alpheus distinguendus, Parapenaeopsishardwickii, Leptochela gracilis, Alpheus juponicus and Palaemon gravieri. In autumn,however,3dominant species were foundwhich were Solenocera crassicornis，Parapenaeopsis hardwickii and Metapenaeus joyneri. Eurythermal and eurysalineshrimp community prevailed in the Jiaojiang River estuary, followed by eurythermaland hyposaline shrimp community.Margalef index(D), Shannon index(H′)andPielou’s evenness index(J′)were used to evaluate the diversity of shrimp communityin the studied area. The stations with higher value of D and H′were mainly located inthe west of the Dachen Island, whereas the Pielou’s evenness index(J′)was stable allthrough the Jiaojiang River estuary.By hierarchical cluster analysis and non-metricmultidimensional scaling(NMDS) method, different shrimp assemblages weredetermined by influential environmental factors such as water depth. The resultsindicated that the shrimp communities had a significant seasonal alteration and spatialvariation. Depth was the most important factor that affected variations in the shrimpcommunity structure in the Jiaojiang River estuary. The result indicated that theaverage weight densities in April and October were7.89kg·km-2and86.20kg·km-2,respectively. Yet the average number densities were11.04×103ind·km-2and34.41×103ind·km-2，respectively. In April，the weight densities in the west studiedarea were higher than those in the east，the number densities were opposite to the weight densities. In October，however，both of weight and number densities in the eaststudied area were obviously higher than those in the west. The shrimps continuallystayed at Jiaojiang coast，in Apirl，especially in northwest where the water is affectedby the runoff of the Jiaojiang. But higher density in southeast waters in October，especially is affected by the Taiwan Warm Current. According to stepwise regressionanalysis on shrimp abundance and hydrological factors，the shrimp abundance hadsignificant correlation with surface temperature(PW=0.004，PN=0.01)，insignificantcorrelations with other factors. In Spring，Acetes chinensis is the most importantdominant species because of its highest contribution rate to the number densities andhigher weight densities. In October，Solenocera crassicornis is the most dominantspecies because of its highest contribution rate to the weight densities and numberdensities（2）There were11species of crab were found in our investigations, whichbelonged to5families under5genera.7species of crab were found inspring(April)and8species in autumn(October).Index of relative importance(IRI)wasemployed to determine the importance of species, Charybdis japonica wasthedominant species in two seasons. Eurythermal and eurysaline crab communityprevailed in the Jiaojiang River estuary, and far more than others. The D and H′weregradually increased from the waters of the west to the east.The results indicatedthat the crab communities had ainsignificant seasonal alteration and spatial variation.The result indicated that the average weight densities in April and October were74.57and62.73kg·km-2, respectively. Yet the average number densities were3.63×103and5.07×103ind·km-2，respectively. InApril，both of the weight and number densities inthe central studied area were higher than those in both sides，In October，however，both of weight and number densities in both sides studied area were obviously higherthan that in the central. The crabs continually stayed at Jiaojiang coast，in Apirl，especially in north where the water was affected by the runoff of the Jiaojiang. Buthigher density in northwest and southeast waters in October，especially was affectedby runoff of the Jiaojiang and the Taiwan Warm Current. According to stepwiseregression analysis on crab abundance and hydrological factors，the crab abundancehad insignificant correlation with temperature and other factors. In Spring andAutumn，Charybdis japonicawas the most important dominant species.