EFFECTS OF VARYING SALINITY AND N:P RATIOS ON THE GROWTH

AND TOXICITY OF Karenia brevis

Abstract

The toxic dinoflagellate Karenia brevis forms extensive red-tides in the Gulf of Mexico releasing brevetoxins which cause implications in human health, and mass mortalities in marine mammals and fish. Historically K. brevis was considered only to bloom above the “salinity barrier” of 24, but recently blooms were recorded near low salinity waters of the Florida Panhandle and the Mississippi River. In this study the SP3 S-tox clone of K. brevis was cultured in salinities of 15, 20, 25, 30, 35 and 40 at three N:P nutrient conditions, Balanced, N-limited and P-limited, to measure the effects salinity and varying N:P ratios on the growth and toxicity of K. brevis. Cultures of K. brevis showed no growth in salinities at 20 and below, and good growth at salinities of 25, 30, 35 and 40. Maximum growth rates varied from 0.36 to 0.64 divisions per day. On average the highest growth rates were in a salinity of 35, and lowest in a salinity of 25. Toxin per cell analyzed with the ELISA Assay showed highest concentration in the 25 N-limited treatment with 100.02 pg-toxin•cell^-1 and 40 P-limited with 99.23 pg-toxin•cell^-1. It appears salinity is the primary factor regulating growth of K. brevis and nutrient additions act as a secondary factor. Salinity acts as the primary factor regulating toxin production with highest toxin per cell at extremes in salinities of 25 and 40, and intermediate at a salinity of 35. Nutrient stress appears to stimulate toxin production in this preliminary study, and a future study examining toxin production under nutrient stress should be performed with multiple ELISA Assays.