Determination of effective parameters on growth and bloom forming of Cochlodinium polykrikoides

Harmful algal blooms resulting in red discoloration of coastal waters in the Persian Gulf, Iran were first observed in January 2007. The species responsible for the bloom, which was identified as Cochlodinium polykrikoides, coincided with massive aquatic organisms’ mortalities in the Persian Gulf. In order to provide optimum growth and bloom forming, C. polykrikoides cells were sampled during the bloom conditions in the coastal waters of Persian Gulf. After adaptation in filtered seawater, they isolated by positive phototropism characteristic of this species to light. They were grown in modified media culture at different salinity (30, 32 and 35ppt), temperature (20, 23, 26 and 28ºC) and intensity (35, 70 and 90 μmol m-2s-1). The results of the present study clearly showed that the highest alga biomass and growth rate was obtained following culture under the 32ppt salinity, 26°C temperature, and under a 12h light:12h dark photoperiod regime at a light intensity of 90μmol m-2s-1 provided by cool white fluorescent tubes. Maximum cell density and growth rate of C. polykrikoides in a 60 liter tank for 20 days reached to 32×106 cell L−1 and 0.28 day-1, respectively. However, the mean obtained cell density of C. polykrikoides in temperature regimes 20, 23, 26 and 28ºC (under salinity of 32ppt, and 90μmol m-2s-1 irradiance) were 2730, 9360, 28240 and 18080 cell ml-1, respectively. A two-way ANOVA indicated significant effects of temperature on the growth rate of C. polykrikoides followed by salinity, and then the interaction between temperature and salinity.