Seasonal distribution of Calanus sinicus (Copepoda, Crustacea) in the East China Sea

On the basis of the four-season investigation in 23°30'~33°N and 118°30'~128°E of the East China Sea from 1997 to 2000,the seasonal distribution of Calanus sinicus was studied with aggregation intensity,regression contribution and other statistical methods.It was inferred that C.sinicus's predominance presented from winter to summer,especially in spring and summer,because its dominance amounted to 0.62 and 0.29 respectively.The percent of its abundance in copepod abundance was 76.71% in summer,greater than 66.60% in spring,greater than 19.02% in winter,greater than 4.02% in autumn.The occurrence frequency in winter and spring was 83.08% and 93.89%,higher than that in summer and autumn,76.71% and 73.87%.Compared with other dominant species of copepods,C.sinicus's contribution to the copepod abundance was obviously greater than that of the other species in winter,summer and spring,but smaller in autumn.C.sinicus tended to have an aggregated distribution.The clumping index peaked in summer (50.19),followed in spring (19.60),declined in autumn (13.18) and was the lowest in winter (3.04).The abundance changed in different seasons and areas,relating to temperature but not salinity in spring and autumn,to salinity but not temperature in summer; to neither temperature nor salinity in winter.In spring and summer,its high abundance area was often located in the mixed water mass formed by the Taiwan Warm Current,the Huanghai Sea Cold Water Mass,the coastal water masses and the Changjiang Dilute Water.In spring and autumn,its abundance was affected by the warm current,as well as the runoff from continental rivers affected it in summer.It can be inferred that C.sinicus was adapted to wide salinity and temperature,as a euryhalinous and eurythermous species in the East China Sea.