The Feeding Ecology Research Of Mesozooplankton In Daya Bay

To explore the feeding behavior of the mesozooplankton community with the impacts of trophic cascade,a two-year serial monitoring program,in situ feeding experiments and reproduction activity of mesozooplankton adults were conducted at a typical eutrophication area near the experimental station in Daya Bay.Through reproduction data,we could discuss what contribution did selective-feeding made to copepods.The current research is aim to shed light on the understanding of energy transformation and effects of trophic cascade in marine plankton food web.The results showed that the abundances of mesozooplankton in Daya Bay during 2015 to 2017 were highest in winter,following by spring,autumn and summer.The dominant mesozooplankton were filter-feeding species,including Temora turbinata,Calanus sinicus,et al.,which were also the control of the grazing behavior in the related plankton food web.The filter-feeding mesozooplankton exhibited a great preference on the microphytoplankton(20-200 ?m)but not on the nano-(2-20 ?m)and the pico-phytoplankton(0.7-2 ?m).The herbivorous feeding of mesozooplankton also showed a clear seasonal patterns with pigment analysis,which showed that dinoflagellates and prasinophytes were the most initiatively preferred prey for the mesozooplankton in Daya Bay in all seasons.In addition,haptophytes and cryptophytes were the supplementary prey for the mesozooplankton in spring,haptophyta and prasinophytes in summer,and diatoms,cryptophytes and Synechococcus in autumn.Diatoms were not the preferred prey for mesozooplankton in Daya Bay,even the biomass reached nearly 50%during the investigated period.In contrast,dinoflagellates,which were considered as high level of nutrition content,were selected as prey even in low concentration.It may be due to mesozooplankton turn to select high nutrition food.Overall,the grazing pressure of mesozooplankton had a minor effect on the biomass of phytoplankton and in turn,were less powerful in the control of phytoplankton biomass in Daya Bay.Then,we further modified the calculation of grazing rate of mesozooplankton on phytoplankton by considering the trophic cascade effects by microzooplankton.In situ grazing experiment indicated that mesozooplankton preferred microzooplankton,such as ciliates,to phytoplankton.It may be due to larger body size and higher nutritional status of the former.The finding that ingestion preference will induce the trophic cascade effects on the whole plankton food web,which were sometimes underestimated during the study of grazing rate of mesozooplankton on phytoplankton.In this study,the grazing rate of mesozooplankton on phytoplankton was recalculated through revised formulas with the consideration of the trophic cascade effects which had an important role in accurately assessing the energy transformation in marine plankton food web.The results showed that the actual grazing rate was-0.04 ± 0.13 d-1 and ranged from-0.59 to 0.43 d-1.The proportion between trophic cascade rate effects rate was from-548%to 1188%and the mean value was 115%± 175%.Meanwhile,microzooplantkon exerted great pressure on phytoplankton and their grazing rate on phytoplankton was 1.59 ±0.69 d-1(0.12?6.08 d-1).The new result confirmed the previous conclusion that mesozooplankton had weak control on biomass of phytoplankton and its grazing pressure on phytoplankton was mainly on microzooplankton.Furthermore,copepods,one of the most important mesozooplankton in Daya Bay,turned to acquire its prey which contain more polyunsaturated fatty acids(PUFA)during selectively-feeding.Particularly,the food which contain more docosahexaenoic acid(DHA)had a key effect on the process of reproduction.The result indicated that diatoms and dinoflagellates played an important role in the reproduction of copepods through principal component analysis(PCA).It may due to the high content of eicosapentaenoic acid(EPA)and DHA in these phytoplankton.Because the biomass of diatoms was high in Daya bay,it was not a limting factor for copepods.Copepods turned to select other food source like dinoflagellates.Mesozooplankton community preferred feeding on ciliates,which however,had no extra fundamental role in the process of copepods' production.It may be due to the lack of ?3PUFA,the essential elements in ciliates.In summary,the selective-feeding behavior of mesozooplankton had a great contribution to the growth,reproduction and other metabolism process of mesozooplankton.During the selective-feeding,mesozooplankton gain different nutritional status of prey to meet their metabolism requirement during the growth.