Surveys were conducted along the northeast coast of the USA, between Portsmouth, NH, and the Chesapeake Bay in 1988 and 1990, to determine the population distribution of Aureococcus anophagefferens, the chrysophyte responsible for massive and destructive 'brown tides' in Long Island and Narragansett Bay beginning in 1985. A species-specific immunofluorescent technique was used to screen water samples, with positive identification possible at cell concentrations as low as 10-20 cells ml-1. Both years, A.anophagefferens was detected at numerous stations in and around Long Island and Barnegat Bay, NJ, typically at high cell concentrations. To the north and south of this 'center', nearly half of the remaining stations were positive for A.anophagefferens, but the cells were always at very low cell concentrations. Many of the positive identifications in areas distant from Long Island were in waters with no known history of harmful brown tides. The species was present in both open coastal and estuarine locations, in salinities between 18 and 32 practical salinity units (PSU). The observed population distributions apparently still reflect the massive 1985 outbreak when this species first bloomed, given the number of positive locations and high abundance of A.anophagefferens in the immediate vicinity of Long Island. However, the frequent occurrence of this species in waters far from this population 'center' is disturbing. Aureococcus anophagefferens is more widely distributed than was previously thought. Numerous areas thus have the potential for destructive brown tides such as those associated with the sudden appearance of the species in 1985.
