COMM UNITY CHARACTERISTICS OF SHRIM PS IN THE OFFSHOREWATERS OF THEM ID2SOUTHERN EAST CHINA SEA

Based on the data of the shrimp resources sampled by single trawler as investigation boat in 18 stations in the offshore waters of the Mid-Southern East China Sea (26°00′N-28°30′N, 121°00′E-126°00′E) in May, August, November, 2006 and February, 2007, total catch from each trawlerwas counted and identified to species in taxonomy, and the spatial variation of the shrimp species composition, index of relative importance (IRI),the diversity and similar characteristics of the community structure were analyzed. 32 species of shrimp were caught in this survey, which belonged to 22 families under 11 genera1 Comparison of the amounts of various species in different seasons: there are 22 species in the autumn which are the most; 20 species in winter, 17 and 18 species in the spring and the summer respectively. According to the standard of index of relative importance (IRI) (the specieswith IRI above 1000 were regarded as the dominant species in this paper), there were 10 dominant species: M etapenaeopsis longirostris, M etapenaeopsis dalei, Solenocera alticarinata, Plesionika izum iae, Ibacus novemdentatu, Parapenaeus fissuroides, Solenocera koelbeli, Solenocera crassicornis, Parapenaeopsis hardwickii and Solenocera crassicornis, and 5 of them were major dominant specieswhich were M etapenaeopsis long irostris, M etapenaeopsis dalei, Plesionika izum iae, Parapenaeus fissuroides and Parapenaeopsis hardwickii. Defined the ones with IRI values ranging from 100 to 1000 as common species, we got 7: M etapenaeopsis barbata, Penaeus japonicus, Plesionika dentirostris, Palaemon gravieri, Alpheus japonicus, Parapandalus spinipes and Sicyonia cristata. The abundance of the dominant species was varied with seasons. For example, 5 were in May: M etapenaeopsis longirostris, M etapenaeopsis dalei, Parapenaeopsis hardwickii, Solenocera alticarinata and Plesionika izum iae, 89.15% of the total catch and 92.14% of the total individuals. In August, there were 7 dominant species: M etapenaeopsis dalei, Plesionika izum iae, M etapenaeopsis longirostris, Parapenaeus fissuroide, Solenocera crassicornis, Ibacus novemdentatus and Solenocera alticarinata, 91.82% of the total catch and 95.05% of the total individuals. In November, the number of dominant species increased to 8: M etapenaeopsis longirostris, Plesionika izum iae, Parapenaeus fissuroides, M etapenaeopsis dalei, Solenocera crassicornis, Ibacus novemdentatus, Solenocera koelbeli and Solenocera alticarinata, occupying 95.31% and　97.56% of the total catch individuals, respectively. In February, the number reduced to 5: M etapenaeopsis longirostris, Parapenaeus fissuroides, M etapenaeopsis dalei, Solenocera koelbeli and Plesionika izum iae, 88.76% and 94.93% respectively. Based on their adaptability to habitats, all recorded species of shrimpswere categorized into the hyperthermal and hysaline community in the Mid-Southern EastChina Sea. The stationswith high abundance were mainly located in the west of the 120m isobaths, and gradually lower toward the autumn to winter, while it reached the lowest in winter1Margalef index (D) and Shannon-Wienner index (H′) were higher in summer and autumn than those in winter and spring, Pielou’s evenness index (J′) in the offshorewatersof theMid2Southern East China Seawas stable through every season. The result indicated that the diversity index west of the 120m isobaths was higher than in the east. By hierarchical cluster analysis and non-metric multidimensional scaling (NMDS) assisted analyzing, the types of shrimp assemblage determined by influential factor such as aquatic system, watermass and salinity etc. in the East China Sea in spring were also discussed in the article, two main assemblages were identified in the offshore waters of the Mid-Southern East China Sea, which were deeper costal shrimp assemblage and out shelf sea shrimp assemblage.