AUREOCOCCUS ANOPHAGEFFERENS - CAUSES AND ECOLOGICAL CONSEQUENCES OF BROWN TIDES IN US MID-ATLANTIC COASTAL WATERS

Aureococcus anophagefferens is a picoplanktonic alga that since 1985 h as bloomed in coastal embayments of the western mid-Atlantic, ranging from Narragansett Bay, Rhode Island, to Barnegat Bay, New Jersey, with greatest incidence of recurrence in Long Island bays, New York. Bloom s of this small alga, referred to as ''brown tide,'' can persist for s everal months during late spring and summer at densities in excess of 1.0x10(6) cells ml(-1). They are not associated with anomalous chlorop hyll a, dissolved oxygen, or inorganic macronutrient (N, P) levels. Me terologically induced reduced flushing rates, elevated salinities, and delivery of micronutrients (e.g. iron) from the watershed have been i mplicated in bloom initiation. Brown tides have had severe detrimental effects on the benthos, especially eelgrass (Zostera marina) and susp ension-feeding bivalves, including bay scallops (Argopecten irradians) and blue mussels (Mytilus edulis). Adult bivalves experience subletha l effects (e.g. inhibition of clearance rates) at Aureococcus concentr ations as low as similar to 2x10(6) cells ml(-1) and mortalities at si milar to 10(6) cells ml(-1), attributed to toxicity of this microalga. Impacts of brown tide on zooplankton are less clear, but reduced egg production rates of copepods and reduced population growth rates of ci liates are documented at higher brown tide concentrations (greater tha n or equal to 1.0x10(6) cells ml(-1)). We summarize the state of knowl edge about the physical, chemical, and biological factors that may con tribute to brown tide initiation, maintenance, and decline and assess its ecological effects.