NUTRIENT BIOEXTRACTION BY SEAWEED FARMING IN NEW YORK CITY, LONG ISLAND SOUND AND OTHER URBANIZED ESTUARIES IN SOUTHERN NEW ENGLAND  

Nutrient Bioextraction is an environmental management strategy by which nutrients are removed from an aquatic ecosystem through the harvest of enhanced biological production, including the farming of seaweeds and/or suspension-feeding shellfish. Seaweeds remove inorganic nutrients from water and shellfish filter organically bound particles rich in nutrients. The combination of these two groups of organisms will extract both inorganic and organically bound nutrients, and therefore, could be a powerful tool in cleaning up nutrient-enriched areas in urban estuaries providing there is a sufficient source of seedstock for economically important seaweeds. Nutrient bioextraction was tested using a red seaweed, Gracilaria tikvahiae and the sugar kelp, Saccharina latissima in Long Island Sound, Bronx River Estuary (New York City) and other urbanized estuaries in New England.  The aquacultured kelp grew as much as 3.0 m in length and had a yield of 18 kg m^-1 (over 110 MT ha^-1) after 5 months (Dec.-May).  Gracilaria grew up to 16.5% d^-1 with over 30 MT ha^-1 of yield during June -Oct. growing season.  Seaweed aquaculture has the potential to remove over 430 kg ha^-1 yr^-1 of nitrogen and over 7,700 kg ha^-1 yr^-1 of CO₂, respectively, if Gracilaria and Saccharina culture were alternated in different seasons.  These results suggest that nutrient bioextraction via seaweed aquaculture can be utilized as an additional nutrient management tool in urbanized estuaries, while producing valuable products to growers.