Viability of Alexandrium tamarense cysts in the sediment of Funka Bay, Hokkaido, Japan: Over a hundred year survival times for cysts

The abundance of Alexandrium tamarense cyst was investigated vertically in a sediment core in Funka Bay, Hokkaido, Japan. Germination experiments were conducted to estimate the germination ability of the cysts at different depth layers of the sediment. Molecular identification with loop-mediated isothermal amplification (LAMP) of A. tamarense cysts and core dating with 210Pb methods (CRS model) were performed. The results indicated A. tamarense has presented since at least 100 years in Funka Bay and intensive bloom started occurring in the early 1960s and has continued until the late 1980s. Cysts from shallow layers of the sediment core displayed greater viabilities than those from deeper layers. However, successful germination of A. tamarense cysts was observed even at the deepest layer, indicating the long-term survival ability (approximately 100 years), and this is the longest record for survival of resting cysts on this species at present. The abundance of viable cysts deposited during the past intensive bloom period was approximately 1.4 times higher than that of recently deposited cysts, suggesting that the cysts in the sub-surface dense layers could potentially function as seed populations in Funka Bay. Thus, dredging the sediment in Funka Bay may involve the risk for initiation of toxic blooms.

► We investigated the abundance of A. tamarense cysts vertically in a sediment core collected in Funka Bay.
► We examined the germination ability of the cysts distributed at different depth layers of the core.
► A. tamarense presents since at least 100 years in Funka Bay.
► We showed A. tamarense cysts have long-term survival ability (approx. 100 years).
► This is the longest record for survival of resting cysts in this species at present.