Seasonal Distribution of Pelagic Ostracoda in the Changjiang Estuary and Its Adjacent Waters

Based on the data from four seasonal oceanographic surveys in the Changjiang Estuary (29°00′~32°00′N and 122°00′~123°30′E) from 2002 to 2003, the seasonal alteration and horizontal distribution of ostracod abundance, as well as the relationship between the ostracod abundance and water masses were studied. Moreover, the environment adaptation of dominant species and their contribution to total ostracod abundance were discussed. The distribution pattern of pelagic Ostracoda was compared with that of the offshore in the East China Sea. The results showed that the seasonal abundance of pelagic Ostracoda differed obviously in the studied waters, and it was highest in spring and lowest in winter. The diversity indices (H’) of pelagic Ostracoda in four seasons were all below 2.00, and the highest was found in winter and the lowest in summer. A total of 20 species of pelagic Ostracoda were identified. The species number of pelagic Ostracoda peaked (16 species) in spring, but only 3 species were found in autumn. Euconchoecia chierchiae was the dominant species in four seasons. In spring Euconchoecia maimai was the most important species for its great contribution to total abundance (β0.90). In winter E. chierchiae was the only dominant species with contribution to total abundance above 0.90. The abundance of E. chierchiae greatly affected the seasonal abundance of ostracods, thus determining the ecological variation of pelagic Ostracoda in the studied areas.