MODULATING EFFECT OF COLD-DARK STORAGE ON EXCYSTMENT IN ALEXANDRIUM-PSEUDOGONYAULAX (DINOPHYCEAE)

The effects of cold-dark conditions on excystment of Alexandrium pseud ogonyaulax (Biecheler) Horiguchi ex Yuki et Fukuyo (Gonyaulacales: Din ophyceae) resting cysts were studied for different lengths of time (0 to 120 d). Cyst populations of the same age were obtained by incubatin g a culture in a diluted growth medium. Cysts that were not exposed to cold-dark conditions showed a long dormancy period and low germinatio n success. A high percentage of excystment, together with a rather syn chronous germination, were observed for cysts exposed to cold-dark con ditions for 40 to 100 d. Shorter (20 d) and longer (120 d) periods of storage in the cold-dark incubator lowered excystment success and germ ination synchrony. These results indicate that low temperatures and ab sence of light during the dormancy period are strongly effective, not only in enhancing germination success, but also in modulating and timi ng the whole excystment process.