Eutrophication thresholds formacroalgal overgrowth of coral reefs

Excessive seawater nutrient concentrations have long been observed to be associated with algal overgrowth of coral reefs, but only recently have studies been done to determine the critical threshold levels. Recent studies from the Caribbean and Australia show that these limits are around one micromole per liter of nitrogen as nitrate and ammonium and one tenth of a miromole per liter of phosphorus in available inorganic and organic forms . These critical levels for coral reefs are perhaps the lowest of any ecosystem, and they are now bemg considerably exceeded in Negril waters according to recent data by Wade (this volume). Analysis of algae collected from Long Bay Negril, and along a transect from Negril Lighthouse to the South Negril River (Goreau, this volume) show that Negril algae are very strongly phosphorus limited, but they are being enriched strongly by land based sources of phosphorus, which is stimulating rapid algal eutrophication of Negril reefs.