Ecological Studies On Zooplankton In Zhelin Bay Of Eastern Guangdong: 2001～2002

Zhelin Bay in one of the most important bays for marine culture in Guangdong Province of China. Due to the increasing human population and mariculture in the last 10 years, ecological environment has changed dramatically. In order to understand why Phaeocystis blooms frequently hit this area and how the increased marine culture affects this ecosystem, locale investigation of phytoplankton, zooplankton, nutrients, and other biochemical parameter were carried out from nineteen stations. This paper describes an annual (7/2001-7/2002) variation of the community structure and temporal and spatial distribution of zooplankton in Zhelin Bay.Zooplankton investigation was conducted in the Zhelin Bay, eastern Guangdong, during the period of July 2001 and July 2002. The investigation identified 60 species of copepod, 3 species of cladoceran, and others such as hyperid amphipod, euphausiid, mysid, polychaete, chaetognoth, tunicate, medusa, and planktonic larva. Micro-zooplankton was dominant in Zhelin bay because the mode of the body length of zooplankton is 0.5 mm though individuals varied from 0.4 mm to 3.5 mm, which may mainly due to that dominant species such as Paracalanus crassirostris, Oithona brevicornis and Penilia avirostris, accounting for 59.6% of the total abundance, were small with body lengths less than 0.6 mm.The dry weight biomass, species diversity and abundance of zooplankton were higher in the samples collected from outside the bay than those within the bay. Similarly, samples of the outer and eastern boundaries of the bay had higher biomass, diversity and abundance than those of the inner and western boundaries. Zooplankton was rare in the mariculture areas of the inner bay, indicating that the large-scale cage fish culture might influence the distributions of zooplankton. Total number of individuals and biomass of zooplankton were positively correlated to water temperature, and their maximum values were observed in August and September when the water temperature was high, and decreased to the lowest in February when the temperature was low. The high annual abundance (14.0 X 103 ind. / m3) and dry weight biomass (208.0 mg ?dw / m3) indicated a rich zooplankton community of this bay. Within the same year, the abundance of zooplankton was positively correlated to the abundance of phytoplankton, but the opposite was observed among different years.In Zhelin Bay, the diversity index (H1 = 2.35) and evenness (J = 0.688) of zooplankton were low. The annual average dominance of Paracalanus crassirostris was 0.366 and was 0.271 of Oithona brevicornis. The high dominances of these two species might be the main reason for the low diversity index and evenness in the Zhelin Bay.