Effect of salinity on the distribution, growth, and toxicity of Karenia spp.

The first recorded bloom of Karenia spp., resulting in brevetoxin in oysters, in the low salinity waters of the Northern Gulf of Mexico (NGOMEX) occurred in November 1996. It raised questions about the salinity tolerance of Karellia spp., previously considered unlikely to occur at salinities < 24 psu, and the likelihood that the bloom Would reoccur in the NGOMEX. Salinity was investigated as a factor controlling Karenia spp. abundance in the field, using data from the NGOMEX 1996 bloom and Florida coastal waters from 1954 to 2004, and growth and toxin production in cultures of Karenia brevis (Davis) G. Hansen and Moestrup. During the NGOMEX bloom, Karenia Spp. Occurred much more frequently at low salinities than in Florida coastal waters over the last 50 years. The data suggest that the NGOMEX bloom started on the NW Florida Shelf, ail area with a higher frequency of Kartnia spp. at low salinities than the rest of Florida, and was transported by an unusual westward surface current caused by Tropical Storm Josephine. The minimum salinity at which growth occurred in culture ranged between 17.5 and 20 psu, but the optimal salinity ranged between low values of 20 or 25 and high values of 37.5-45 psu, depending on the clone. The effect of salinity on toxin production in one clone of K. brevis was complex, but at all salinities brevetoxin levels were highest during the stationary growth phase, Suggesting that aging, high density blooms may pose the greatest public health threat. The results demonstrate that Karenia spp. can be a public health threat in low salinity areas, but the risk in the NGOMEX is relatively low. No bloom has occurred since the 1996 event, which was probably associated with a special set of conditions: a bloom along the Florida Panhandle and a tropical storm with a track that set up a westward current. (c) 2005 Elsevier B.V. All rights reserved.