Toward a theory of biological-physical control of harmful algal bloom dynamics and impacts

A growing body of laboratory, field, and theoretical work suggests that the dynamics of harmful algal blooms and their impacts on other organisms are frequently controlled not only by physiological responses to local environmental conditions as modified by trophic interactions, but also by a series of interactions between biological and physical processes occurring over an extremely broad range of temporal and spatial scales. All too frequently, major gaps in our ability to identify, measure, and model the underlying biological and physical processes and their interactions over the appropriate temporal and spatial scales have prevented the quantitative assessment of the importance of these factors in causing past blooms and the development of predictive models of bloom dynamics and impacts. For these reasons, we have combined fluid continuity equations with a conservation equation for population dynamics to quantify how biological and physical processes and their interactions affect the population dynamics of harmful algae and their potential impact on other organisms. Applications of the resulting numerical and conceptual models to toxic algal blooms in upwelling systems and pycnocline layers suggest not only that bloom dynamics and impacts are sensitive to biological-physical interactions occurring at multiple scales, but also that such interactions may be critical components of the life-history strategies of these organisms.