A review of the causes, effects, and potential management of harmful brown tide blooms caused by Aureococcus anophagefferens (Hargraves et Sieburth)

Brown tides caused by the harmful alga Aureococcus anophagefferens abruptly appeared in some coastal embayments of the northeastern United States (Rhode Island, New York) in 1985. Since then, brown tides have vanished from some bays, chronically reoccurred in others, and recently have exhibited an apparent southern expansion into new regions (e.g., New Jersey, Delaware, Maryland, and Virginia). Brown tides have also recently been detected across the Atlantic Ocean in South Africa. Although blooms of A. anophagefferens have no known direct, negative effects on human health, they are considered harmful because of their detrimental effects on estuarine organisms, such as suspension feeders (scallops and hard clams) and submerged aquatic vegetation. The selective effect of blooms on pelagic grazers (zooplankton and shellfish) is likely to affect food webs and biodiversity within affected ecosystems. Recent findings indicate brown tides occur in shallow estuaries with long residence times and high salinities (> 25‰). These estuarine characteristics may foster the accumulation of algal biomass and a nutrient environment (high dissolved organic matter and low dissolved inorganic nitrogen) as well as a low light regime that encourages rapid cellular growth of A. anophagefferens. A lack of sufficient grazing control by benthic and pelagic suspension feeders during the initiation phase of blooms is also implicated in brown tide development.