Growth, primary productivity, and nitrogen fixation potential of Nodulariaspp. (Cyanophyceae) in water from a subtropical estuary in the United States

Nodularia is a halotolerant, filamentous, dinitrogen-fixing cyanobacterium that forms massive blooms in some coastal oceans, estuaries, and saline lak es worldwide. Although the genus is globally distributed, its blooms are sp oradic and appear to be confined to certain water bodies. Blooms are freque ntly associated with phosphorus enrichment; therefore Nodularia may benefit from increased anthropogenic nutrient loading to coastal waters, We studie d the potential for Nodularia to grow in the nitrogen-limited Neuse River E stuary (North Carolina, U.SA.) with laboratory growth experiments in Neuse River Estuary water and by examining physico-chemical data from the estuary . Analysis of nutrients (nitrogen and phosphorus), salinity, and temperatur e data from the Neuse River Estuary between 1994 and 1998 revealed that sui table conditions for Nodularia prevailed during the sum mer of each of thes e years for time spans ranging from 1.5 to 5 months, Growth of two laborato ry strains in Neuse River Estuary water was as fast or slightly slower than in artificial growth medium, as long as the culture inoculum had phosphoru s reserves. Phosphorus addition did not stimulate growth of already phospho rus-sufficient inocula, Phosphorus starvation of the inoculum before the ex periment decreased growth rates in the estuarine water unless additional ph osphorus was supplied. Although phosphorus addition had a stimulatory effec t on dinitrogen fixation and productivity, the effect differed for the two Nodularia strains. Results suggest that growth of Nodularia in North Caroli nian estuaries is possible, and that such growth would be phosphorus-limite d at times. Phosphorus availability may determine the times and locations f or potential establishment of Nodularia in this and similar estuarine ecosy stems.