Distribution pattern of pelagic amphipods and its affecting facors in the East China Sea

On the basis of data from four seasonal cruises in the East China Sea (23°30'~33°N, 118°30'~128°E) from 1997 to 2000, horizontal distribution of amphipods, seasonal variations of abundance and their dynamic mechanisms were approached with quantitative and qualitative methods.Results showed that the average value of amphipod abundance in autumn was 115×10^-2 ind./m³, the highest in four seasons.The second occurred in summer with a mean value of 44×10^-2 ind./m³ and the lowest occurred in spring with a mean of 10×10^-2 ind./m³.Amphipods were hardly observed in the north nearshore (29°30'~33°N and 122°30'~125°E) in winter and spring.In all seasons, except for the north of the sea in autumn and the south in summer, the abundance in the offshore area was higher than that nearshore.The major species influencing the amphipod abundance were Lestrigonus schizogeneios in spring, L.macrophthalmus and L.schizogeneios in summer, L.bengalensis and Hyperioides sibaginis in autumn and Gammarus sp.in winter.The amphipod abundance showed a prominent linear correlation with the surface water temperature, but no significant correlation with both other water temperatures and salinity in spring.It was found that water temperature and salinity were not significantly correlated with the variation of amphipod abundance in summer, autumn and winter.In addition, the amphipod abundance in all four seasons can be linearly correlated with the bottom water temperature.The highest abundance area was located in the mixture waters near the side of warm water current in summer.Peak of amphipod abundance in autumn, not in summer told a temporal process for amphipods to develop their populations.The continuance of warm current was beneficial to the development of amphipod abundance from summer to autumn.Amphipods are kinds of very important diets for fishes in the offshore East China Sea.