Electron Transport System Activity And Carbon Demand Of Zooplankton At Different Size Classes In The Antarctic Amundsen Sea

Zooplankton（mainly including krill,copepods,nudibranchs,pteropods,etc.）,play an important role in the structure and function of the Southern Ocean food web and ecosystem.Zooplankton communities can regulate ecosystem structure and func-tion by influencing biogeochemical cycles,carbon fluxes and food web interactions.In this study,based on zooplankton samples collected using Norpac nets（mesh:330μm,network port:0.5 m²）in the Antarctic Amundsen Sea in summer during the 34th Chi-nese Antarctic Scientific Expedition（2017/2018）and the 35th Chinese Antarctic Sci-entific Expedition（2018/2019）,we investigated the composition,abundance,carbon biomass and community structure of zooplankton and the influence of We investigated the composition,abundance,carbon biomass and community structure of zooplankton,as well as the biotic and abiotic factors affecting the zooplankton community,and we also investigated the activity of the zooplankton electron transport system and carbon demand at different particle size classes.A total of 35 zooplankton species were identified based on 2017/2018 samples from the Amundsen Sea,of which the total abundance and biomass of 15 species made a major contribution（more than 90%）to the zooplankton community structure.Re-dundancy analysis revealed that environmental factors（e.g.,temperature,nitrate,dis-solved oxygen,ammonium）explained more than 40%of the variation in zooplankton abundance/biomass,suggesting that physical and chemical processes jointly drive zoo-plankton community variation.Also,there was a significant positive correlation be-tween zooplankton abundance and biomass and phytoplankton and ciliate abundance and biomass,suggesting trophic linkages among various zooplankton functional groups.The zooplankton data from both 2017/2018 and 2018/2019 cruises were pooled for redundancy analysis,and the results showed that silicate and ammonium salts played a major role in the variation of zooplankton abundance and biomass.After dividing the zooplankton samples from 2017/2018 and 2018/2019 into grain size classes,it was found that the highest mean abundance of zooplankton was found in the 200-500μm grain class with 169.60 ind m^-3 and the lowest mean abundance of zooplankton was found in the>2000μm grain class with 15.54 ind m^-3;while in terms of biomass,the>2000μm grain class The average biomass of zooplankton was the highest at 3.82 mg C m^-3 and the lowest at 0.16 mg C m^-3 in the 200-500μm class.Electron transport system activity and carbon demand calculations for zooplank-ton samples from 2017/2018 and 2018/2019 revealed that when using zooplankton electron transport system activity wet weight per unit expressed in terms of and carbon demand wet weight per unit,the mean values of zooplankton electron transport system activity and carbon demand were greatest for particle size classes 200-500μm,respec-tively 145.88μl O₂ g-1 wet wt h-1 and 1594.28μg C g^-1 wet wt d^-1,respectively,while the mean values of zooplankton electron transport system activity and carbon demand for particle size classes>2000μm were the smallest at 58.24μl O₂ g^-1 wet wt h^-1 and636.47μg C g^-1 wet wt d^-1,respectively;the analysis of total zooplankton The mean values of electron transport system activity and carbon demand of zooplankton in the particle size class>2000μm were 4.53μl O₂ m^-3 h^-1 and 49.57μg C m^-3 d^-1,respec-tively,and the mean values of electron transport system activity and carbon demand of zooplankton in the particle size class 200-500μm were the smallest,0.79μl O₂ m^-3 h^-1and 8.63μg C m^-3 d^-1,respectively.Carbon requirements of zooplankton communities of different grain sizes in the Amundsen Sea were mainly influenced by wet weight,which may be related to envi-ronmental factors and the structure of the zooplankton community.Pearson correlation analysis between zooplankton electron transport system activity and carbon demand with environmental factors and zooplankton community abundance and biomass re-vealed that dissolved oxygen,seawater temperature,PO₄-P,NH₄-N,Si O₃-Si and NO₃-N,as well as gastropods（Gastropod）,copepods（Copepod）,polychaetes（Polychaete）,Ostracod,Chaetognath and Amphipoda all affected the activity of the electron transport system and carbon demand of zooplankton（p<0.05）.