Circannual excystment of resting cysts of Alexandrium spp. from eastern Gulf of Maine populations

Species of the marine dinoflagellate Alexandrium, present in most of the Gulf of Maine (GOM), Bay of Fundy and Gulf of St. Lawrence as well as in many other areas of the world, are known to cause toxicity to marine organisms and humans alike. Excystment of Alexandrium fundyense from the eastern region of the GOM (Penobscot Bay to Bay of Fundy) was followed through four germination cycles (4 years). An annual, free-running oscillation in germination was observed under constant environmental conditions, indicating control by an endogenous clock for these eastern cysts, as shown earlier for cysts from the western region of the GOM. This circannual endogenous clock had an average period of 11 months. The phase of germination remained constant for cysts from all three stations sampled. Cysts did not germinate, despite favorable growth conditions, in summer-to-fall and this timing was consistent among cysts from all stations. The timing of cyst germination is highly relevant to modeling of Alexandrium sp. bloom initiation and depletion, as there are cyst “seed beds” near shore and offshore in the eastern and western regions of the GOM.