Cyst Formation in the Red Tide Dinoflagellatealexandrium Tamarense(dinophyceae): Effects of Iron Stress¹

The toxic red tide dinoflagellate Alexandrium tamarense (Lebour) Balech (synonymous with Protogonyaulax tamarensis (Lebour) Taylor) was subjected to iron stress in batch culture over a 24‐day time course. Monitoring of life history stages indicated that iron stress induced formation of both temporary (= pellicular) and resting (= hypnozygotic) cysts. Our experimental induction of sexuality appeared to be associated with iron limitation rather than the total depletion of biologically available iron. Degenerative changes in organelle (i.e. chloroplast, mitochondrion and chromosome) ultrastructure were largely restricted to pellicular cysts, suggesting that these temporary cysts were more susceptible to short‐term iron stress effects than were hypnozygotes. These results are consistent with the hypothesized ecological roles of cysts in maintaining viability over brief (pellicular cysts) and extended (hypnozygotes) exposure to adverse environmental conditions.