Pia H. Moisander and Hans W. Paerl
Abstract
Nodularia is a halotolerant, filamentous, dinitrogen (N2) -fixing cyanobacterium that forms massive blooms in some coastal oceans, estuaries and saline lakes worldwide. Although the genus is globally distributed, blooms are sporadic and appear to be confined to certain water bodies. Blooms are frequently associated with phosphorus (P) enrichment; therefore Nodularia may benefit from increased anthropogenic nutrient loading to coastal waters. We studied the potential of Nodularia to grow in the nitrogen (N)-limited Neuse River Estuary (NRE) (North Carolina, USA) with laboratory growth experiments in NRE water and by examining physico-chemical data from the estuary. Analysis of nutrients (N and P), salinity, and temperature data from the NRE between 1994-1998 revealed that suitable conditions for Nodularia prevailed during the summer of each of these years for time spans ranging from 1.5-5 months. Growth of laboratory strains in NRE water was as fast or slightly slower than in artificial growth medium, as long as the culture inoculum had P reserves. Phosphorus addition did not stimulate growth of already P-sufficient inocula. P starvation of inoculum prior to the experiment decreased growth rates in the estuarine water unless additional P was supplied. While P addition had a stimulatory effect on N2 fixation and productivity, the effect differed for the two Nodularia strains. Results suggest that growth of Nodularia in North Carolina estuarine waters is possible, and that growth may be at times P- limited. Phosphorus availability may determine the times and locations for potential establishment of Nodularia in this and similar estuarine ecosystems.
URL: http://www.es.ucsc.edu/~piam/
Revised--Oct 12, 2004