Diurnal Rhythm of Zooplankton Community Structure in the Surf Zone of Daliaohe River Estuary in Spring

The diurnal rhythm of zooplankton community structure was investigated in the surf zone of Daliaohe River estuary on April 24~25, 2013. The results showed that the zooplankton assemblage was composed of 16 species in total, belonging to 4 taxonomic groups and 16 species or genera including 11 freshwater ones and 5 brackish ones, with predominant species were protozoa Difflugia sp.,rotifera Keratella cochlearis,copepoda copepodid and Cyclops sp. The peak zooplankton density(4504.28 ind.·L-1)was observed at 8:00 a.m, protozoa and rotifera accounting for 78.0% of total density, and being the main factors affecting the diurnal rhythm of density. The peak zooplankton biomass(23.757mg·L-1)was found at 8:00 p.m on April 25, 2013, copepoda representing 99.5% of total biomass, and 91.6% of the average biomass. Moreover, the significant positive correlation was observed between the species composition of zooplankton and the species composition and cell density of phytoplankton in the surf zone of Daliaohe River estuary. The abundant zooplankton in early spring provided a fairly good ecological environment for gonadal development, and reproduction of fishes.