VARIATION IN SPECIES NUMBER AND BIOMASS OF ZOOPLANKTON IN TYPICAL ESTUARIES OF CHINA

Zooplankton is sensitive to environmental changes caused naturally or anthropically. The zooplankton distribution and changes in number of species and biomass major estuaries of China were studied for estuaries of Changjiang (Yangtze) River, Pearl River and Huanghe (Yellow) River. Data used in this paper were collected in May and August from 2004 to 2006 by the State Oceanic Administration of China. The data were analyzed against available previous data of the same area and season. The results show that, since 1958—1960, the number of zooplankton species decreased by 50.6% and copepoda by 53.3% in the Huanghe River Estuary, the proportion of copepoda in zooplankton decreased from 42.4% in 1985 to 32.6% in 2006. In the Changjiang River Estuary, the number of zooplankton species slightly changed, but that of copepoda decreased from 62 in 1985 to 37 in 2006; the proportion of copepoda in zooplankton decreased from 54.2% in 1958 to 42.5% in 2006. In the Pearl River Estuary, the proportion of copepoda in zooplankton decreased from 59.3% in 1959 to 54.4% in 2006, and no clear change was found as limited by available data. Compared with the results of 1958— 1960 marine survey, the zooplankton biomass in spring and summer in the Huanghe River Estuary changed slightly, mostly in summer. The average biomass of zooplankton in springs of 2000 to 2006 was 528.36 mg/m3 in the Changjiang River Estuary, being 2.4 times over that of 1958, similarly for the summer biomass for 2.2—2.7 times higher. In the Pearl River Estuary, the spring biomass has significantly increased from 1959 to 2004—2006 by 5.7—8.7 times, while that of summer biomass in 1981 and 2006 increased by 3.1 and 11 times over that of 1959, respectively. Therefore, all the three estuary areas show a tendency of increase, the largest in the Pearl River Estuary, and followed by the Changjiang River Estuary and the Huanghe River Estuary in turn.