NUTRIENT STRUCTURE CHARACTERISTICS OF FISH COMMUNITY IN SEAWEED BEDS OF GOUQI ISLAND,ZHOUSHAN BASED ON STABLE ISOTOPE ANALYSIS
In order to clarify the nutritional structure of fish communities in the coastal seaweed beds of Gouqi Island,Zhoushan,China,the δ13C and δ15N values of the fish community samples were measured using stable carbon and nitrogen isotope techniques.The contribution rate of potential food sources to various consumers in different seasons were calculated based on Isosource mixture model and seasonal variation of nutritional structure of fish communities were analyzed accordingly.Results illustrating that during flourishing period of the seaweed beds,δ13C values of the fish in the coastal waters of Gouqi Island ranged from-20.4‰～-12.8‰,with an average of-16.1‰,and the δ15N values ranged from 4.1‰ to 10.4‰,with an average of 8.4‰.However,during the decline period,the δ13C values ranged from-17.9‰to-14.4‰,with an average of-16.1‰,and the δ15N values ranged from 7.6‰ to 12.9‰,with an average of 9.7‰.The high trophic fish(such as juvenile black seabream)fed more on fish and shrimps.The most contribution rate of food sources for Scorpaenidae(such as juvenile Sebastiscus marmoratus and Agrammus agrammus)were from gammarid and Caprella acanthogaster;Zooplankton provided main food sources for Clupeidae fishes(such as Thrissa kammalensis and Collichthys lucidus and Pseudosciaena polyactis).Five quantitative indexes were calculated by Siber model,whose results indicates the values of niche space,core niche space,basic food source and nutrient diversity of common fish communities in flourishing period were higher than.those in declining period.The algal field in flourishing period supported a higher biodiversity and food diversity of fish was greater.The nutrient length of the two seasons were equal and common fish had relatively stable food net structure and nutritional diversity level.
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