INTERACTIVE EFFECTS OF SALINITY AND TEMPERATURE ON PLANOZYGOTE AND CYST FORMATION OF ALEXANDRIUM MINUTUM (DINOPHYCEAE) IN CULTURE

1. Low P/N ratios seem to induce gamete expression because the percentage of planozygotes recorded in the absence of added phosphate (-P) was significantly higher than that obtained in the absence of added nitrogen (-N), or when the concentrations of both nitrogen and phosphate were 20 times lower (N/20 + P/20). 2. Salinity (S) and temperature (T) strongly affected both planozygote and cyst formation, as sexuality in the population increased significantly as salinity decreased and temperatures increased. S, T combinations that resulted in no significant cyst formation were, however, favorable for vegetative growth, ruling out the possibility of negative effects on cell physiology. 3. The initial cell density is thought to be important for sexual cyst formation by determining the chances of gamete contact. However, the inoculum concentrations tested did not explain either planozygote formation or the appearance of resting cysts.