Refining the Niche of Harmful Dinoflagellates through Intensive Observation of Blooms within a Retentive, Inshore Embayment

Harmful algal bloom dinoflagellates are among the most extensively studied species of marine phytoplankton both in situ and in laboratory settings through the growth and manipulation of cultures. Among many other applications, cultures are commonly used to explore changes in growth and behavioral responses across a broad range of physical and chemical parameters. Our own research group has published an extensive set of laboratory experiments to establish the growth and behavioral responses by the PSP species Alexandrium fundyense to changes in temperature and nutrient availability among other factors. In turn, results from these studies have been the basis of a biological sub-model within spatially explicit, coupled physical-biological models of A. fundyense bloom development in the Gulf of Maine and the Nauset Marsh estuary (Cape Cod, MA). More recently, through integrated observation and modeling of blooms within the Nauset Marsh estuary, our work has indicated that this culture-based approach grossly underestimates the physiological performance of A. fundyense cells in situ. Natural populations of A. fundyense divide faster, swim faster, and are inducted into the sexual phase of their life cycle at much higher rates than has been reported from studies of laboratory cultures. In spite of these flaws, assessments of the Gulf of Maine and Nauset models have demonstrated surprising skill at replicating large-scale patterns observed in field studies of this organism. One explanation may be that current models apply unrealistic grazing rates and other loss processes associated with species-species and cell-cell interactions. In situ observations by automated instruments provide a means to address these deficiencies by providing new ways to evaluate model performance, including comparisons of modeled and observed rates of division and broader consideration of species dynamics within the phytoplankton assemblage.