| Zhelin Bay is one of the most important bays for mariculture in Guangdong Province of China. Since the 1980's, mariculture increased rapidly there, which resulted in the exacerbation of estuarial eutrophication and incessant depravation of ecological status. Especially, two large-scale Phaeocystris pouchetii blooms, which made the enormous economic loss on the local fish farming and the seriously ecological destroy on environment, occurred there in the end of 1997 and in July, 1999. Owing to its benignly lee geographic condition, Shen'ao Bay, opposite to Zhelin Bay, is the only water region of net-trunk mariculture in Nan'ao Island. Through the annual (7/2000-7/2001) investigation of species composition, distribution and seasonal variation of zooplankton in Zhelin Bay and Shen'ao Bay, the paper analyzed their ecological status and their variational trend in the future, and will ulteriorly give basic data for studying and formulating the strategies on continuing development and estuarial ecological protection of mariaquaculture in eastern Guangdong Province.Locale investigation of plankton, chemical and physical elements was carried out from eleven stations twice every one month in winter, three or four times in other seasons. Sampling was scheduled to cover the period around high tide (+1.5hr). In each station, water samples for zooplankton analysis was collected by double vertical hauls of a JP-2 net (200 u m) from the bottom to the surface. Two batches of samples were collected once every month. One batch was fixed immediately with formalin (5%) in situ and then transferred to laboratory for species identification and biomass analysis. Thereinto, copepod, and cladocera were identified to species, others were identified to genus. The other batch was used for dry weight measurement. Samples were filtrated through glass fiber filtering membrane(Waterson, GF/C) without fixation, rinsed with 6.5% isoosmotic ammonium formate, desiccated with the vacuum pump, and dried in the oven at 60C for 24 h. Then they were cooled to indoor temperature in the desiccator, and measured with OHAUS analytical balance. One batch of samples were collected in other sampling time every month. The diversity index (H') evenness (J) and dominance (Y) were calculatedaccording to Shannon-weaver (1949), Pielou (1969) and Curtis(1951).In Zhelin Bay, our investigation found 57 copepods and 3 cladocera, but in Shen'ao Bay, only 30 copepods and 3 cladocera. In terms of individual abundance, copepod accounted for the largest percentages (65.28% & 68.24%) in the two bays, followed by planktonic larvae (13.16% & 15.37%) and cladocera (10.74% & 9.19%). Micro-zooplankton dominated the zooplankton community. Although the body length of zooplankton individuals varied from 0.4mm to 3.5mm, its peak value is 1.1 mm and 0.9 mm in Zhelin Bay and Shen'ao Bay. Moreover, the dominant species in the two bays are both Paracalanus crassirostris, Oithona brevicorni and Penilia avirostris, which body length were less than 0.6 mm.In Zhelin Bay and Shen'ao Bay, the species abundance, biomass and total individuals of zooplankton increased from the inner bay to the outer bay. In the marine culture areas of their inner bays, there were usually low values indicating the large-scale filter-feeding oyster culture and marine fish culture were suspected to have important influences on the distributions of zooplankton. In the two bays, monthly means of species number and total individuals also exhibited a single peak during our investigation period with the annual means of 13.3 species and 11.2 species, 6.8 X 103indiv./m3 and 4.7X103 indiv./m3. Temporally, the highest species abundance was found in August (38 species and 24 species) and the lowest was in January (17 species and 7 species). Total individuals peaked in September (17.8 X 103ind./m3) and decreased to the lowest in January (0.63X 103ind./m3) in Zhelin Bay. In Shen'ao Bay, the highest in August (10.7X 103 indiv./m3) and the lowest in February (0.29 X 103 indiv./m3. In the two bays, annual variation of...
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