COMMUNITY CHARACTERISTICS OF SHRIMPS IN THE OFFSHORE WATERS OF THE MID-SOUTHERN EAST CHINA SEA

Abstract

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 trawler was 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 genera. 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 species with IRI above 1000 were regarded as the dominant species in this paper),there were 10 dominant species:Metapenaeopsis longirostris,Metapenaeopsis dalei,Solenocera alticarinata,Plesionika izumiae,Ibacus novemdentatu,Parapenaeus fissuroides,Solenocera koelbeli,Solenocera crassicornis,Parapenaeopsis hardwickii and Solenocera crassicornis,and 5 of them were major dominant species which were Metapenaeopsis longirostris,Metapenaeopsis dalei,Plesionika izumiae,Parapenaeus fissuroides and Parapenaeopsis hardwickii. Defined the ones with IRI values ranging from 100 to 1000 as common species,we got 7:Metapenaeopsis 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:Metapenaeopsis longirostris,Metapenaeopsis dalei,Parapenaeopsis hardwickii,Solenocera alticarinata and Plesionika izumiae,89.15% of the total catch and 92.14% of the total individuals. In August,there were 7 dominant species:Metapenaeopsis dalei,Plesionika izumiae,Metapenaeopsis 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:Metapenaeopsis longirostris,Plesionika izumiae,Parapenaeus fissuroides,Metapenaeopsis 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:Metapenaeopsis longirostris,Parapenaeus fissuroides,Metapenaeopsis dalei,Solenocera koelbeli and Plesionika izumiae,88.76% and 94.93% respectively. Based on their adaptability to habitats,all recorded species of shrimps were categorized into the hyperthermal and hysaline community in the Mid-Southern East China Sea. The stations with 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 winter. Margalef 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 offshore waters of the Mid-Southern East China Sea was 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,water mass 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.