A size-based ecosystem model for pelagic waters

Size-based models offer a holistic approach to understanding the structure and function of pelagic ecosystems, compared to simple models in which the entire system is represented by a single phytoplankton and zooplankton species. In this study, a one-dimensional size spectral model is constructed to simulate the temporal and vertical variability in the microbial community, nutrients and primary productivity. The approach taken is based on published allometric relationships governing physiological and ecological processes for phytoplankton and zooplankton. Since these allometric relationships are objective estimators of ecological parameters and are not dependent on knowledge of particular species, these models can be used to describe general features of the ecosystem. The model is driven by light, temperature and nutrient availability and is applied to an oligotrophic system in the Sargasso Sea-the Bermuda Atlantic Time Series (BATS) station, where field data on size spectra has recently been acquired. The model is able to reproduce the general overall features of this oceanic ecosystem fairly well: It depicts a late winter/early spring bloom and low production during the summer and fall months. In addition, a deep subsurface phytoplankton biomass maximum is produced in the summer, consistent with field measurements. The model prediction for size spectra is reasonably successful, although further refinement is necessary. As a whole, the model is fairly robust and can also be applied to ecosystems of different trophic state.