What Controls Microzooplankton Biomass and Herbivory Across Marginal Seas of China?

Hongbin Liu, Hong Kong University of Science and Technology, Division of Life Science, Hong Kong, Hong Kong, Kailin LIU, Hong Kong University of Science and Technology, Life science, Hong Kong, Hong Kong, Bingzhang Chen, University of Strathclyde, Department of Mathematics and Statistics, Glasgow, United Kingdom, Bangqin Huang, Xiamen University, State Key Laboratory of Marine Environmental Science, Xiamen, China, Liping Zheng, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China and Suhong Su, Marine Environment Monitoring and forecasting Centre, Zhangzhou, China
Microzooplankton play a critical role in marine food web and biogeochemical cycling. To explore the potential mechanisms controlling microzooplankton biomass and community grazing rate, we have conducted numerous experiments to measure microzooplankton biomass and grazing rates across a vast area of China marginal seas. We also constructed a model that incorporated Metabolic Theory of Ecology and theory of grazing functional responses to quantify the effects of temperature, phytoplankton (Chl a) concentration, and microzooplankton biomass on microzooplankton grazing rate measured by the dilution technique. Our results showed that the biomass-specific microzooplankton grazing rate increased with increasing temperature and decreased as phytoplankton biomass increased when the phytoplankton biomass exceeds 15 μg C L-1. The model with Holling III grazing function characterized the effect of temperature with a temperature sensitivity of 0.42 eV and well described the pattern of biomass-specific microzooplankton changing with phytoplankton biomass with a maximum grazing rate of 4.25 d-1 and a half saturation constant of 0.18 μM N. We also found that microzooplankton biomass was strongly correlated with Chl a concentration, but not with temperature. The relationship between microzooplankton and phytoplankton biomass followed a power law function with a scaling exponent of 0.82 ± 0.06, which is well consistent with a pervasive pattern found in predator- prey relationships in diverse terrestrial and aquatic ecosystems. In addition, we found that the community composition of microzooplankton was affected by the trophic status with more heterotrophic dinoflagellates in eutrophic waters. The model we constructed provides a robust foundation to predict how ecological communities respond to the climate change, and can serve as a basis for estimating microzooplankton community grazing rate and biomass from environmental predictors, particularly in China seas.