Microzooplankton grazing dynamics: parameterizing grazing models with dilution experiment data from the California Current Ecosystem

Coupled physical-biological models are essential tools for enhancing our understanding of the potential effects of long-term climate change on planktonic ecosystems in the world's ocean. A major impediment to utilizing such models is obtaining accurate parameterizations of the modeled rate processes, such as growth and grazing. The California Current Ecosystem Long-Term Ecological Research (CCE-LTER) program has generated detailed data of phytoplankton growth and zooplankton grazing rates obtained in the field by the dilution technique. Here, we examine how data from dilution experiments can be used with nonlinear grazing models to study the dynamics of microzooplankton grazing. We use data from experiments conducted in 2007 to parameterize 3 different grazing functions and then test them against a more extensive data set from a CCE-LTER process cruise in 2006. We found that system-level parameterizations of the functional response relationships, representing the aggregate behaviors of predators and prey adapted to different environmental conditions, reasonably predict the shapes and magnitudes of vertical profiles of microzooplankton grazing in both coastal and open-ocean environments in the CCE. Predicting the magnitude of grazing rates-as opposed to just the concentrations of grazers-presents a much greater challenge for models in previous studies. Model-data comparisons are often difficult due to the lack of extensive data from different environments. Our study is a significant advance in the parameterization of zooplankton grazing models in the field and will serve as a solid base on which to pursue further studies of the planktonic ecosystems of the northeastern Pacific.