Subtidal Volume Fluxes, Nutrient Inputs and the Brown Tide—an Alternate Hypothesis

Data and calculations recently published by others show that unusual meteorological and hydrological conditions reduced the flushing rate of Great South Bay and other embayments on Long Island, New York, during the spring of 1985. These observations led to a hypothesis that the resulting increase in retention of inorganic nutrients from land played an important role in establishing conditions necessary for the dramatic brown tide of Aureococcus anophagefferens that bloomed in these, and other nearby systems, in the spring and summer of that year. We present an alternate hypothesis that is consistent with the physical observations, but more compatible with the nutrient budget of Great South Bay and with recent evidence suggesting that Aureococcus blooms are associated with low inputs of inorganic nutrients. The normal flux of dissolved inorganic nitrogen into Great South Bay from the coastal ocean appears to be about 15 times greater than the input from land drainage. The hydrological conditions of spring 1985 would therefore have reduced the major source of inorganic nutrients to the bay rather than increasing nutrient availability. While a reduction in nutrient input may seem inconsistent with initiation of a nuisance algal bloom, there is increasing evidence from field surveys and controlled mesocosm experiments that the growth of Aureococcus is favoured by oligotrophic conditions.