Fish community pattern and its relation to environmental factors in the Beibu Gulf

Based on data collected by quarterly otter trawl surveys in the Beibu Gulf in 2007,fish species compositions and community pattern were analyzed.A total number of 323 fish species belonging to 101 families and 18 orders were collected during the surveys.The largest number of species was recorded in winter (231 species),followed by those in autumn and summer (217 and 214 species,respectively),and the number of fish species was the smallest in spring(186 species).The spatial pattern of fish community was analyzed using hierarchical clustering and non-metric multidimensional scaling.Five station groups based on fish assemblages were indentified.The Group Ⅰ was located in the coastal waters of northeast Beibu Gulf and showed less seasonal variation in distribution.The Group Ⅱ was located in the coastal waters west off Hainan Island.The Group Ⅲ covered a large area of the central and southern waters of the Beibu Gulf,while the Group Ⅳ located near the Bailongwei Island covered the least stations,and the Group Ⅴ can only be identified in spring season to the west Qiongzhou Strait.The ANOSIN tests showed highly significant differences (R=0.896-0.956,P<0.001) in fish assemblages between the station groups.The relationships between changes in fish community pattern and environmental factors (depth,bottom temperature and bottom salinity) were examined.The correlation analysis showed that the water depth was the major environmental factor dominating the fish community pattern,while bottom temperature and salinity contributed less to determining the community pattern.