Thermal niche of the dinoflagellate Karlodinium veneficum across different salinity and light levels

Abstract The interactive effects of temperature (15–30°C), salinity (5–30) and light (low-100 and high-300 μmol photons m−2 s−1) on growth, thermal niche properties and cellular carbon (C) and nitrogen (N) of the toxic dinoflagellate, Karlodinium veneficum, were studied to understand its potential for change under future climate conditions in the eutrophic Chesapeake Bay. Cell growth was highest under conditions of 25–28°C, salinity 10–20 and high light, which represented the preferred physical niche for bloom formation in the present day. In the Chesapeake Bay, blooms generally occur at 25–29°C and salinity 10–14, while low-biomass occurrences have been found at salinities 15–29, consistent with the laboratory findings. High light increased the thermal sensitivity of K. veneficum and lowered the thermal optima for growth. Under conditions of low light, and salinity 10–20, cells exhibited the highest thermal optima for growth. The highest upper thermal maxima were observed at salinity 30, suggesting that cells in the lower estuary would be more thermally resistant than those in upper and mid-estuarine regions, and therefore these higher salinity regions may provide over-summering habitats for K. veneficum. Cellular C and N were highly varied at the preferred salinity and temperature niche and C:N ratios showed decreasing trends with temperature.