Successful management of the coastal environment requires sound knowledge of the biological, chemical, and physical processes governing the growth, retention, dispersion, and transport of water constituents, including plankton. The growing problem posed by the existence of harmful plankton species now demands a thorough understanding of the life histories and population dynamics of these organisms. Without this knowledge, managers can neither assess the impact of anthropogenic activity on the environment and biota, nor understand the relationship between harmful phytoplankton species and the harmful events (commonly referred to as harmful algal blooms [HABs]) caused by them, and climate. Without this understanding, the desirable goals of prediction and mitigation of harmful events are unattainable. A major challenge is to understand the processes governing the population dynamics to a level of detail that allows mathematical formulations that are relatively simple, yet reproduce the salient features of HAB population dynamics.