The effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides were examined in the laboratory. From 60 different combinations of temperature (10-30°C) and salinity (10-40) under saturated irradiance, C. polykrikoides exhibited its maximum specific growth rate of 0.41 day-1 at a combination of 25° C and salinity of 34. Optimum growth rates of >0.3 day-1 were observed at temperatures ranging from 21 to 26° C and at salinities from 30 to 36. The organism did not grow at temperatures ≤10°C and only grew at salinities >30 if the temperature was >15°C. It was able to grow in temperatures ranging from 15 to 30°C and at salinities from 20 to 36. These values closely resembled those observed for this species in situ. It appears as if C. polykrikoides is a stenohaline organism that prefers high salinities, indicative of offshore waters. Temperature had the greatest influence on the growth rate, followed by salinity, and then the interaction between temperature and salinity. The optimum irradiance for growth was >90 μmol m-2 s-1. Photoinhibition did not occur at 230 μmol m-2 s-1, which was the maximum irradiance used in this study.
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