Diel vertical migration of dominant planktonic crustaceans in the south branch of Yangtze Estuary,China

Zooplanktons are important food organisms of fishes,and their spatial and temporal distribution pattern has an important influence on the growth and reproduction of fishes in local habitats.The Yangtze River Estuary of China is rich in fishery resources,but the knowledge on the distribution pattern of zooplankton in this area is still very limited.The diel vertical migration(DVM)patterns and seasonal variations of the crustacean community,and their relationship with environmental factors were investigated in the south branch of the Yangtze Estuary,from June 2017 to May 2018.The results showed that the dispersion patterns of dominant crustacean taxa in the Yangtze Estuary were mostly aggregated.Migration amplitudes of crustacean were greater in spring and summer than in autumn and winter,and different migratory patterns occurred in different seasons.Sinocalanus dorrii,Schmackeria inopinus,Mesmackeria leuckarti,Bosmina longirostris,and B.fatalis,unlike S.forbesi,showed a significant DVM.The DVM patterns of crustaceans was possibly influenced by light dentisy,temperature,and total dissolved solids in the water column,and the fish predation effect;whereas,the nutrient concentration and pH were not supposed to be key factors.