Predicting potentially toxigenic Pseudo-nitzschia blooms in the Chesapeake Bay

Harmful algal blooms are now recognized as a significant threat to the Chesapeake Bay as they can severely compromise the economic viability of important recreational and commercial fisheries in the largest estuary of the United States This study describes the development of empirical models for the potentially domoic acid producing Pseudo-nitzschia species complex present in the Bay developed from a 22-year time series of cell abundance and concurrent measurements of hydrographic and chemical properties Using a logistic Generalized Linear Model (GLM) approach model parameters and performance were compared over a range of Pseudo nitzschia bloom thresholds relevant to toxin production by different species Small threshold blooms (>= 10cells mL(-1)) are explained by time of year location and variability in surface values of phosphate temperature nitrate plus nitrite and freshwater discharge Medium (100 cells mL(-1)) to large-threshold (1000 cells mL(-1)) blooms are further explained by salinity silicic acid dissolved organic carbon and light attenuation (Secchi) depth These predictors are similar to other models for Pseudo nitzschia blooms on the west coast suggesting commonalities across ecosystems Hindcasts of bloom probabilities at a 19% bloom prediction point yield a Heidke Skill Score of similar to 53% a Probability of Detection similar to 75% a False Alarm Ratio of similar to 52% and a Probability of False Detection similar to 9% The implication of possible future changes in Baywide nutrient stoichiometry on Pseudo-nitzschia blooms is discussed (C) 2010 Elsevier BV All rights reserved