EFFECTS OF SALINITY AND LIGHT INTENSITY ON GROWTH AND TOXICITY OF THE MARINE DINOFLAGELLATE

Abstract

The effects of differing extrinsic environmental factors on growth rates and influences on toxin production were investigated in the dinoflagellate Karlodinium veneficurn isolated from the Chesapeake Bay. Effects varied on the production of Karlotoxins and growth rates under a light gradient of 7.0, 26.5, 46.2, 60.5 µmot m⁻² s⁻¹ and salinity densities of 10, 15, 20, 30, 35 psu in monocultures of Karlodinium veneficum grown under semi-continuous conditions at a constant temperature. Among the light treatments significant slower growth occurred at 26.5 and 46.2 µmol 111-2 s⁻¹. At the lowest light intensity (7.0 µmol m⁻²) cells died within 4-8 days of inoculation. Although growth was not significantly different across the salinity gradient, there were noticeable differences between the highest average growth rate occurring at 20 psu and the slowest growth at 35 psu. On two different occasions after cultures reached a steady growth state, cellular toxicity was tested for hemolytic activity based on lysis of rainbow trout erythrocytes. Percent hemolysis for the differing light and salinity gradient experiments demonstrated significant mean differences among treatments. One-way ANOVA for both light intensity and salinity on both testing occasions showed significantly different hemolytic activity. The average hemolytic activity for the two intermediate light treatments was 45%, 68.5% and for the salinity treatment at 35 psu was 51.5%. Flow cytometry provided histograms of DNA analysis indicating with decreased light intensity there was an increase in percentage of cells in the G1 phase and decrease in percentage of cells in the S + G2 growth phase of the cell cycle. In cultures where salinity conditions were altered there was a positive relationship between salinity and number of cells in the G1 phase corresponding with decreasing number of cells in the S + G2 growth phase. The data from cells cultured at 20 psu suggest that there is a decreased number of intact cells and possible degradation of the DNA as indicated by the broader G1 peak. Cell cycle data from higher salinity cultures of 30 and 35 psu is not shown due to a marked decrease in cell numbers and significant DNA degradation. The results for the light treatments suggest toxin production in K. veneficum is an indirect response to light, coupled to growth rates. Growth rates were not significantly influenced by salinity suggesting toxicity in K. veneficum is uncoupled from growth and a direct response an environmental stress, possibly osmotic. K. veneficum is known to be very toxic responsible for massive fish kills in estuarine and marine coastal environments; it is imperative to further investigate and understand the effects of extrinsic environmental factors on growth and toxin production. Additional investigation could help determine exogenous mechanisms for toxin production and facilitate a better understanding of this toxic species bloom dynamics.