| Marine zooplanktons act as the intermediate link between the low trophic levels and the high trophic levels in the planktonic food chain. They play functional roles in material and energy transfer in the marine ecosystem. In addition, the selective grazing of zooplankton community has significant effects on the community structure and biomass of phytoplankton, and consequently influences the whole ecosystem. Their diel vertical migration(DVM) behavior of zooplankton and dirnal feeding pattern are of great importance in the energy transfer from upper layer to the bottom layer in the water column. On the other hand, zooplankton grazing pressure is probably most direct and widely considered biological factors to limiting phytoplankton biomass. Grazing pressure differ not only among grazer species, but also at different developmental stages within one species. The grazing of zooplankton, as an updown control factor, could contribute to the demise of algal blooms.We firstly studied the special and seasonal distributions of marine cladocerans in Daya bay the through 4 cruises(2013-07-06, 2013-10-25, 2014-01-27, 2014-04-21).The peak of zooplankton biomass occurred in spring and summer in this area while relatively low in autumn and winter. Spring is the peak of cladocerans biomass and its dominant species is Evadne tergestina. The zooplankton biomass is relatively higher in bay inshore waters than outside, and the overall level of productivity increased in Daya Bay. The change of Daya bay surrounding environment has a significant effect to zooplankton community and structure, and seasonal variation. The seasonal change trend of zooplankton abundance and biomass had changed, and the presence of the peak time to move the spring. This study provided the important basic data of Daya bay for study of ecosystem dynamics and the utilization of biological resources.Phytoplankton and zooplankton assemblages at various layers of Daya Bay in the autumn of 2014 and DVM behavior of zooplankton were investigated. The diurnal variation of chlorophyll a concentration showed a similar trend of early in the morning and in the evening is reduced, rising at noon. A different pattern was represented in the diatoms biomass, suggesting a strongly influence of zooplankton feeding. There was differerence in the distribution pattern of copepodamong different layers at different time points. Authough the composition of diet differed for dominant species at different layers; diatom was generaaly, the most important preys, accouting for 46%, 41% and 67%at surface, middle, and bottom layers, respectively. The DVM pattern varied among different dominant species, such as Temora stylifera and Acrocalaus longicornis migrated twice a day, whereas some Temora turbine and Acrocalaus gibberonly once. For the others species Acartia erythraea, viously, the DVM behavior was not that obvious or no pattern could not be recognized. The DVM of zooplankton is the result of the external environment and internal physiology. Distribution of phytoplankton was involved in the DVM behavior while no significant effects of temperature and salinity were detected in this present study..Finally, the potential grazing pressure of common species of copepod Pseudodiaptomuspoplesia on A. anophagefferens was studied. Our results showed that the ingestion rate of mesozooplankton responded to the cell density of A. anophagefferens in a manner of Michaelis-Menten function. Copepodids and adults selected against A. anophagefferens,whereas the grazing avoidance was not that strong in nauplii. We speculated that the adverse effect of A. anophagefferens was attributed to the poor nutrition of this speceis. It was suggested that the brown tide was subjected to the suppression from nauplii of copepod during the development afterwards phases but from copedids and adults during the climax phase. |
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