Elevated organic nutrient ratios associated with brown tide algal blooms of Aureococcus anophagefferens (Pelagophyceae)

phyte alga Aureococcus anophagefferens Hargraves et Sieburth occurred in the coastal bays of Long Island NY, Barnegat Bay NJ and Narragansett Bay, RI. During the past 15 years, Aureococcus has bloomed more frequently in Long Island bays than in Barnegat and Narragansett Bays, with significant blooms (>100 000 cells ml–1) occurring in about half of those years. In an intensive survey for the presence of Aureococcus along the eastern coast of the United States, the alga was found to be present only in samples collected north of New Jersey (Anderson et al., 1993). While numerous samples were taken from Maryland, Delaware and Virginia coastal bays, Aureococcus was not detected in any of these samples. Early in 1999, however, Aureococcus was found within several Maryland and Delaware coastal bays (D. Hutchins, personal communication) suggesting that this organism is either spreading or that earlier samples were collected at times or in locations when Aureococcus was not present in sufficient numbers to be detected. Although not directly toxic, Aureococcus has caused significant damage to the ecosystems in which it has bloomed, especially Long Island. Blooms of Aureococcus increase light attenuation in the water column, and have been implicated in the massive loss of eelgrass (Zostera marina) meadows on Long Island (Dennison et al., 1989) due in part to a high minimal light requirement for eelgrass growth (Dennison et al., 1993). Seagrass beds in general are very important nurseries for fish and shellfish. This loss of eelgrass beds has had an indirect impact on shellfish populations on Long Island due to poor juvenile recruitment (Tettelbach and Wenczel, 1993). Directly, Aureococcus has been linked to reductions in reproductive potential [(Tracey, 1988), but see (Tettelbach et al., 1999)] and growth (Gallager et al., 1989) in shellfish, especially the bay scallop. The sudden onset of a monospecific bloom over such a wide geographical area led to an initial hypothesis that these blooms were related to the reduced flushing of these coastal bays owing to rainfall levels that were lower than the long-term average [(Cosper et al., 1989; Vieira and Chant, 1993) but also see (Nixon et al., 1994)]. Other hypotheses have centred around particular trace metals (e.g. iron) and organic constituents being present that stimulate the growth of Aureococcus (Cosper et al., 1993; Gobler, 1995). Recently, LaRoche et al. modified the reduced rainfall hypothesis to suggest that reduced rainfall decreases the input of dissolved inorganic nitrogen (DIN; specifically NO3) which in turn leads to an increase in the dissolved organic nitrogen (DON) to DIN ratio (LaRoche