Integrated Modeling of Harmful Algal Genus Pseudo- Nitzschia to Support Ecosystem Prediction and Environmental Management in the Southern California Current System

The toxigenic harmful algal diatom genus Pseudo-nitzschia (PN), and its potent neurotoxin domoic acid (DA), are considered the leading cause of Harmful Algal Blooms (HABs) for much of the U.S. West Coast, with severe consequences to aquatic life and human health. The connections between HABs and anthropogenic nutrient enrichment, coastal processes (e.g. upwelling), and climate forcing are critical lines of investigation, yet the relative importance of these drivers has not been systematically evaluated. Parsing these drivers and the resulting ecological interactions requires an integrated modeling approach, validated against available observations. Here, we detail the development of a mechanistic model of PN physiology and DA production that leverages previous laboratory studies and is designed to be embedded in realistic, three-dimensional ocean biogeochemical models. The model is based on the hypothesis that nutrient ratios (Si:N) and temperature exert a fundamental control on the timing and magnitude of DA production by PN. We show results from a model configuration that reproduces years of nutrient limitation experiments with chemostat cultures of PN. We further discuss an initial implementation of the model within a realistic three-dimensional physical-biogeochemical configuration for the Southern California Current. We conclude by discussing the potential roles of natural and human drivers (e.g. coastal nutrient inputs) for the development and dynamics of DA-producing HABs.