The Effect of Temperature on Vegetative Growth and Sexual Reproduction of Two Diatoms from the Genus Haslea Simonsen

The effect of temperature on sexual reproduction and the rate of vegetative division were investigated in laboratory experiments with Haslea ostrearia (Gaillon) Simonsen from the Atlantic and H. karadagensis Davidovich, Gastineau et Mouget from the Black Sea. In the range of 10–26°С, a temperature increase was favorable for vegetative growth; the maximum growth rate was recorded at the highest temperature of the range. In contrast to vegetative growth, sexual reproduction of both algal species was effective in the temperature range of 10–18°С, but did not occur at temperatures of 23°С. The optimal temperature for auxosporulation was in H. karadagensis somewhat lower than in H. ostrearia. The determined physiological optimums for sexual reproduction can explain the cell-size distribution that is characteristic of the natural population of H. karadagensis in different seasons of the year.