Heterosigma akashiwo (Raphidophyceae): On prediction of the week of bloom initiation and maximum during the initial pulse of its bimodal bloom cycle in Narragansett Bay

A 38-year time series based on weekly sampling of the annual cycle of the ichthyotoxic raphidophyte, Heterosigma akashiwo, in Narragansett Bay was analyzed in quest of establishing whether predictive indices of its blooms there were possible. The objective was to aid potential man agers of the aquaculture and fish-farming activities being proposed for Narragansett Bay in their de velopment of harmful algal bloom monitoring strategies to protect against product and financial loss. There was a 94% probability that Heterosigma akashiwo would appear during a given year, with de tectable levels (100cells I"1) rarely occurring before week 20. There was an 86% probability that the initial, annual appearance of Heterosigma akashiwo would not occur until watermass temperatures reached a threshold of 10 to 11°C. Following Heterosigma's appearance, there is then an 80% proba bility that its bloom maximum will occur sometime between weeks 23 to 26, and a 66% probability that a second bloom would occur between weeks 43 to 46. The application of these predictors in de veloping a monitoring strategy for use by local aquaculturists and fish-farmers is then outlined.