Seasonal abundance and distribution of Pelagic Euphausiids in the Changjiang Estuary,China

The pelagic euphausiids of Changjiang Estuary and its adjacent waters (29°00'-32°00' N and 122°00'-123°30'E),the 3rd largest estuary in the world located and largest river in China. District,were studied from May 2002 to March 2003. Eight species were recorded but three were dominant species according to their seasonal occurrence; Pseudeuphausia sinica was dominant in the four sampling seasons (0.41,0.62,0.50 and 0.30); dominant species for spring,autumn and winter was Euphausia pacifica (0.03,0.08 and 0.10) while the Euphausia nana was during spring and autumn (0.03 and 0.04). The months in which each species was abundant are given. P. sinica attained the highest densities with the β values in spring (0.87),summer (0.99) and winter (0.78) within the littoral waters of the study area. E. pacifica and E. nana preferred a high salinity warm water. The relationship between the pelagic euphausiids and ecological characteristics were likewise considered. The abundance peak in summer (10.46ind/m3) and lowest abundance in winter (0.32ind/m3). These results suggest that seasonal abundance of euphausiids was influenced the seasonal surface temperature while the horizontal distribution was influenced the surface salinity in the waters of the estuary. The ecological characteristics of Changjiang River contributed to the spatial and temporal distribution of pelagic Euphausiids including P. sinica. Physical environmental factors play a major role in determining the abundance and distribution of pelagic Euphausiids and the dynamics of seasonal cycle.