Ecological Studies On Phytoplankton In The Large-scale Mariculture Of Zhelin Bay, Eastern Guandong: 2001～2002

Zhelin Bay with water area of 68-70km2 is one of the most important estuaries for large-scale mariculture in the eastern Guangdong, China. Our research group had finished an initial study on the ecosystem of phytoplankton. In the present study, I added eleven stations to the primary eight one and finished a second annual investigation on the ecosystem, in order to find out more information on the spatial and temporal distribution of phytoplankton in Zhelin Bay. The thesis presents the investigated results, the ecological characteristic of phytoplankton and the relation between phytoplankton and nutrients.Among 183 taxa, diatom (143) were accounted for 77.8%, followed by dinoflagellates (34), the others (6). Diatom was the dominant group in total phytoplankton. The density of Skeletonema costatwn accounted for 71.0% of the total phytoplankton. Therefore the horizontal and seasonal distributions patterns of S. costatum dominated the patterns of the total phytoplankton.Species, the diversity index (H ' ) and evenness(J) of phytoplankton community increased gradually from inside of the bay to outside of the bay, and was greater in the outer bay than that in the inner bay. The density of total cell number increased from inside of the bay to outside of the bay, and was greater in outer and eastern bay than these in inner and western bay. Chlorophyll a was greater both in the estuary of Huanggang River and outside of bay, but less in the other regions in the bay.The annual averages of the density of phytoplankton and Chl.a showed two peaks. The abundance of phytoplankton remained dominant from July to October in 2001, and gradually decreased from October in 2001 to February in 2002. The density began to rise from March, and up to the peak in April. However, the phytoplankton exceptionally decreased again from May to July in 2002. The result showed that the density was negative correlation with dissolved phosphorus, so phytoplankton was more limited by phosphorus.The percentage of density of S.costatum in phytoplankton rised from 58.7% in last year to 60.0% in this year, which resulted a decline of the diversity index from 1.91 to 1.75, and evenness from 0.47 to 0.42, indicating that the biodiversity and evenness of phytoplankton community in Zhelin Bay became worse and worse, and the structure of community retrogressed.