Olsen Y, Andersen T, Gismervik I, Vadstein O
Metazoan, Protozoan, coastal eutrophication, Assimilation efficiency, Growth efficiency, Carbon feeding rates, Carbon release rates, mesocosm, Hopavagen, Norway, 38 m3
The objective of the present study was to study the dynamics of protozoan and metazoanzooplankton food webs in coastal NE Atlantic waters exposed to variable nutrient input. Data werederived from a mesocosm experiment (7 units, 40 m3, 12 m deep) receiving variable nutrient input.The food web included 3 autotrophic groups based on size, and 4 functional heterotrophic groupsmainly based on trophic position. Inverse modelling was used to construct networks of carbon flowsfor the planktonic food web. Heterotrophic nanoplankton, microplankton and mesoplankton (HNP,CIL and COP, respectively) were found to be equally important contributors to grazing and carbonrelease during undisturbed summer situations. The release of dissolved organic carbon by zooplanktonwas comparable to that of phytoplankton. Autotrophic food was generally more important for zooplanktonthan heterotrophic (mean 75%). Assimilation and growth efficiencies (AE and GE, respectively)of zooplankton groups in undisturbed situations were in the range of 33 to 69% and 10 to 41%,respectively. Values were inversely related to gross primary production (GPP). Sedimentation rates ofcarbon were low. High nutrient input rates increased food availability and most CIL and COP carbonflows. HNP did not respond, and neither did its food, that is, bacteria and picoautotrophs. Theresponse in biomass was generally lower than that for the flows. Values of AE and GE of the zooplanktonduring high nutrient input and food availability varied between 11 and 29% and 5.7 and19%, respectively, and throughout were lower than at low nutrient input. The sedimentation rate ofparticulate carbon increased strongly, resulting in an enhanced organic input rate in deep water.