ECOLOGICAL CHARACTERS OF EUCHAETA CONCINNA (COPEPOD) IN THE EAST CHINA SEA

Based on the data from seasonal oceanographic survey in the East China Sea (23°30′—33°N, 118°30′—128°E) during 1997—2000, the authors discussed the ecological characteristics of Euchaeta concinna population in the East China Sea with analytical methods of aggregation indices and regression contribution. Comparison of the observations made between 1979—1980 and this investigation was carried out. The abundance of E.concinna showed a clear seasonal change in following order: autumn (14.11ind/m~3)winter (0.64ind/m~3)summer (0.39ind/m~3)spring (0.06ind/m~3). E.concinna predominated mainly in pelagic copepods in autumn. In spring, the copepods took only 0.78% of the total pelagic copepods, 1.87% in summer and 5.79% in winter, but 25.12% in autumn. All the clumping indices (I) of the species were negative through the year and peaked in autumn, except for being positive 1.34 along northern offshore in summer. The autumn peak indicated the phenomenon of aggregation. Ambient factors influencing the abundance of E.concinna were selected on the basis of step-wise regression. The results showed that the abundance in autumn and summer were remarkably correlated with bottom salinity, whereas they showed less significant correlation with other ambient factors. The overall abundance in four seasons was clearly related to bottom temperature. Compared with the results obtained in 1979—1980, this study revealed that dominance and abundance of E.concinna in the area have increased, indicating that the ecological importance of E.concinna in pelagic copepods have been developing in the East China Sea. This phenomenon may be related to global warming. Environmental changes in bottom water, especially in warm currents, were the main factors affecting the abundance of E.concinna. However, because they can tolerate in low temperature, for example, 14—16℃ in spring and 12—16℃ in winter in northern nearshore of East China Sea. The population densities were more than 1.00ind/m~3. E.concinna was not a good indicator of warm currents, reflected by the second high occurrence frequency (89.23%) and average abundance (0.64ind/m~3) in winter. The high-abundance area of E.concinna in northern area of East China Sea would provide some clue to local fisheries.