Study On Zooplankton Community Ecology Based On Body Size Theory In South China Sea And East China Sea

As the key link in the energy transfer chain from primary producers to higher trophic levels of the food web,zooplankton plays an important supporting role in the sustainable development of fishery resources.Global oceans,including the East China Sea?ECS?and the South China Sea?SCS?,are facing the stress of marine ecosystems degradation and decline of marine fishery resources.In the present study,the size data and classification of mesozooplankton were obtained by ZooSCAN system to explore the spatial and temporal distribution on the size structure and trophic structure of zooplankton communities in the northern SCS?NSCS?and the southern ECS.How they response to the environmental changes were also investigated.In the NSCS,based on mesozooplankton samples collected in the northern SCS from December 2014 to January 2015,spatial variations of mesozooplankton in biomass,abundance,normalized biomass size spectra?NBSS?,size structure and trophic structure were analyzed.The response of mesozooplankton community to the influence of highly variable oceanographic environment were detected as follows.The river plume and cold eddy are typical highly productive regions(net primary production>400 mg C m^-2 day^-1)with high zooplankton biomass(495.52 mg m^-3 and348.34 mg m^-3,respectively)and high NBSS intercept?5.63 and 4.93,respectively?.No consistent spatial variation was observed for the slope of NBSS,probably because of highly dynamic marine environment in the NSCS.There was a negative correlation between slope of NBSS and Chl a concentration in the river plume and the continental shelf.The ratio of total carnivores biovolume to herbivores/omnivores biovolume?RTCH?was significantly high in river plume and Kuroshio intrusion?0.76 and 0.52,respectively?which may be due to extreme high proportion of smaller size individuals supported by discharge of river and transport of warm water species from the tropical western Pacific by Kuroshio intrusion,respectively.Highly proportion of carnivorous zooplankton is not benefit for reducing the energy lose in zooplankton community and transferring to higher trophic levels.In southern ECS,mesozooplankton samples were collected in four seasons of 2019.Zooplankton biomass was higher in spring and summer(1515.54 mg m^-3 and 1484.05mg m^-3,respectively)than in autumn and winter(282.68 mg m^-33 and 84.81 mg m^-3,respectively).Supported by fast-growing herbivorous and omnivorous zooplankton,carnivorous zooplankton grew in large numbers in spring and summer.RTCH was higher in spring and summer?1.09 and 1.35,respectively?than in autumn and winter?0.33 and 0.57,respectively?,indicating herbivorous and omnivorous zooplankton were under stronger top-down control in spring and summer.Thus,RTCH could reflect the productivity of environment.The top-down control of zooplankton to phytoplankton could be enhanced by elevated zooplankton size diversity through the widening of food size range and increasing of utilization efficiency.GAMMs showed that compared with ESD,zooplankton size diversity could explain more of the distribution of top-down control on phytoplankton.Based on the comprehensive analysis of zooplankton biomass,NBSS,size diversity and ESD,zooplankton biocapacity was higher off shore than near the coast,and was higher in spring and summer than in autumn and winter in the offshore of northern ECS.