Distribution And Community Characteristics Of Zooplankton In The Northwest Coastal Waters Of Hainan Island

Based on the148zooplankton samples collected from21stations in the northwestcoastal waters of Hainan Island during periods of autumn, in2008and winter, spring andsummer in2009, the zooplankton community structure, distribution, seasonal changes wereanalyzed. The relations of the zooplankton diversity with enviromental factors werediscussed. The main results were as follows:A total of154zooplankton species and17pelagic larvae groups were identified basedon the data of four cruises, of which89species occured in autumn and summer,70species inwinter,63species in spring. They belonged to Cnidaria, Ctenophora, Mollusca, Arthropoda,Chaetognatha and Chordata.The annual average total abundance of zooplankton was268.98ind./m3, and an obvioustrend of winter>autumn>spring>summer was obtained. The total abundance showed a highlypositive correlation with total biomass in autumn, winter and spring. And the total abundancewere highly positive correlated with salinity in autumn.The annual average total zooplankton biomass was428.17mg/m3, with a mean valuefluctuations of winter>autumn>spring>summer. The total biomass showed a negativecorrelation with temperature in autumn.The zooplankton in the Northwest coastal waters of Hainan Island might be divided intothe three ecological groups: warm-temperate group, warm-water group and eurythermicgroup and the warm-water group accounted for domination.The dominant species of survey area were Subeucalanus subcrassus, Sagitta enflata,Canthocalanus pauper, Diphyes chamissoni, Lensia subtiloides, Pleurobrachia globosa, S.pulchra, Temora turbinate, Acartia spinicauda, Calanopia elliptica, Euconchoecia aculeate,etc, in which, Subeucalanus subcrassus, Sagitta enflata and Canthocalanus pauper occurredduring four cruises.The species number, total abundance and total biomass of two continuous stationsshowed obvious changes during day and night. Analysis found that the diurnal variation werelittle correlation with tide. And infer that light may be a major cause of diurnal variation ofzooplankton. The species diversity index with a mean value of2.12appeared in summer,2.05appeared in autumn,1.69appeared in spring and1.58in winter. The evenness index showedan obvious trend of summer (0.76)＞spring (0.63)＞autumn (0.62)＞winter (0.50). Therichness index of autumn (5.04) and summer (4.44) was higher than that of winter (3.96) andspring (3.27). The species number, richness index and diversity index were highly positivecorrelated with salinity, while the species number was highly positive correlated withtemperature and salinity in winter. The diversity index, evenness index and richness indexshowed a highly positive correlation with salinity in spring. And the richness index anddiversity index were highly positive correlated with salinity in summer.In spring and winter, according to the zooplankton species composition at each station,two groups were distinguished by using the method of cluster analysis: GroupⅠlocated inthe21station with low salinity, GroupⅡ were warm-water community. In autumn, threegroups were differentiated for the zooplankton: GroupⅠwere coastal low-salt community,GroupⅡ were nearshore warm-water community and Group Ⅲ were widely distributedwarm-water community. In summer, three groups were differentiated for the zooplankton:GroupⅠwere high-salinity community, GroupⅡwere nearshore warm-water community andGroup Ⅲ were widely distributed warm-water community. It was because the station21waslocated in the shore that it was an independent community in autumn, winter and spring.Results of assessment on water environment quality level show that the water quality ofoffshore was better than nearshore and the water quality of summer was better than winter.Pollution from land-based source may be main reasons affecting the water quality.