Zooplankton community ecology in north and south branches at Yangtze River estuary

The special ecological environment at Yangtze River estuary makes zooplankton there different from other water in ecological characteristics such as species composition,density and time-space distribution etc.Two times' investigations were taken in spring(drought season) and autumn(raining season) from2005 to 2006 along the north and south branches,where three cross-section and 20 survey points were set.A total of 227 zooplankton species were identified,with 65 species of rotifers,107species of protozoas,15 species of cladocerans and 40 species of copepods.The Keratella,Polyarthra trigla,Brachionus calyciflorus,Difflugia,Arcella,tintinnid,Calanus sinicus,Sinocalanus dorrii,Mesocyclops leuckarti and Bosmina ect were the dominant species.This paper compared the species composition and structure of two branches.The zooplankton species,quantity and biomass in south branch is higher than that in north branch.Zooplankton community similarity in two branches is very low.The different environmental caused much different zooplankton community structure.Correlationship of zooplankton community structure and environmental factors were analyzed,among which water temperature was the important factor that determined the time distribution of zooplankton with seasonal change.The salinity influenced the ecological types and space distribution of zooplankton community structure.As a whole,the north and south branches were controled by Yangtze river,so that the zooplankton species were mainly rever-type and the salt-type appeared more in section 3.