Size-fraction of Phytoplankton and Photosynthetic Carbon Flow Pathway in the Coastal Area of Zhangzidao Island

Abstract:

To investigate the seasonal and spatial distribution of phytoplankton in terms of Chlorophyll a (Chl a) in the scallop Patinopecten yessoensis aquaculture area of Zhangzidao island, northern China, four filed investigations were conducted in June 2011, October 2011, December 2011 and April 2012. Chl a was further divided into pico-phytoplankton (< 2 μm), nano-phytoplankton (2-20 μm) and micro-phytoplankton (>20 μm) size fractions. Results showed that the concentration of Chl a in the surface and bottom seawater of Zhangzidao area ranged from 0.07-6.28 µg/L and 0.16-5.28 µg/L, respectively, and the related average was (1.60±1.38) and (1.31±1.10) µg/L. There were significant differences in the concentration of Chl a among different seasons (P<0.05). The differences of Chl a’s concentration between surface and bottom seawater were highly significant during autumn and spring (P<0.01). Nano-phytoplankton was the most important size-fraction regardless of surface and bottom seawater and accounted for 50.85% and 44.64% of the total phytoplankton, respectively. CCA analysis of the main environmental factors showed that NO3-, PO43- and NH4+ contributed greatly to nano-phytop­lankton while seawater temperature and NO2- gave a great contribution to pico-phytoplankton. The annual photosynthetically produced particulate organic carbon (PPOC) in this area ranged from 40.31 to 1017.64 mg C/(m2·d) with an average value of (386.07±281.80) mg C/(m2·d). More than 38.3% of the fixed carbons by the photosynthesis were taken by the classical food web via the microbial food loop. These results highlight the important role of the microbial loop in aquaculture system of Zhangzidao coastal area.