Distribution characteristics of pelagic Amphipoda in the Changjiang Estuary and adjacent waters

Seasonal oceanographic cruises were conducted in the waters of the Changjiang Estuary(28b00c~32b00cN and 122b00c~123b30cE)from 2002 to 2003.Based on the data from the investigation,the seasonal distribution and abundance of pelagic Amphipoda in the Changjiang Estuary were dicussed through aqualitative and quantitative method.The relationship of pelagic Amphipoda abundance with the fish ground, the abundance variation of dominant species and thier contribution to pelagic Amphipoda abundance were all considered.It was found that the seasonal Amphipoda abundance was influenced by the seasonal surface temperature.Moreover,the horizontal distribution of its abundance was influenced by the surface salinity in the waters of the estuary.The abundance was the highest(2.75ind./m³)in summerand the lowest(0.10ind./m³)in winter.Of the 49 species identified,Monoculodes limnophilus and Lestrigonus schizogeneios were the mostly dominant species.Monoculodes limnophilus was dominant species in four seasons;it was the main dominant specie in spring,summerand autumn affected by the characteristics relatively low temperature warm adaptation compared with Lestrigonus schizo geneios who was dominant specie just in spring summer and autumn.The contribution of Lestrigonus schizogeneios to Amphipoda abundance was 0.87,higher than Monoculodes limnophilus in sum merattributed to tropical wateradaptation.There was a significant correlation between abundance and the surface temperature,and was no significant correlation with surface salinity.As animportant dietoffish in the Changjiang Estuary,the Amphipoda distributionis important in the fishingground there.