Size fraction of phytoplankton and the contribution of natural plankton to the carbon source of Zhikong scallop Chlamys farreri in mariculture ecosystem of the Sanggou Bay

The biomass and size fraction of phytoplankton in terms of chlorophyll a (Chl a) was measured during four cruises conducted in April, July, October 2013 and January 2014 in mariculture area, the Sanggou Bay, China. Results show that total Chl a levels in the surface seawater of the Sanggou Bay generally range from 0.10 to 20.46 mu g/L, with an average value of 2.13 mu g/L. Nano-phytoplankton was the most important size-fraction and accounted for about 65.1% of total Chl a. In order to evaluate the importance of the protozoan trophic link for energy transfer from the microbial loop to filter-feeding feeders, Zhikong scallop Chlamys farreri was then offered a natural planktonic community as potential prey. Results show that scallops obtained carbon source from natural plankton with the rate of 11 033.05 mu g/(g.d). Protists (nanoflagellates and ciliates) were the dominant source of carbon retained by scallop (48.78%). The microbial loop provided 58.45% of the carbon source for farmed scallops. These results indicate that the microbial loop represent a valuable trophic resource in mariculture system of the Sanggou Bay.