Germination characteristics of Alexandrium catenella cysts from surface sediments in Quartermaster Harbor, Puget Sound, Washington, USA

The dinoflagellate Alexandrium catenella causes frequent outbreaks of paralytic shellfish toxins (PSTs) in Puget Sound, Washington; however, little is known about its basic biology and ecology. Most of what is known is inferred mainly from shellfish toxin records and recent work on cyst distribution and germination potential. We report on a year-long study of cyst dormancy and germination potential based on experiments using surface sediment collected from a shallow embayment, Quartermaster Harbor, in Puget Sound. Cyst abundance in Quartermaster Harbor was 1550–1750 cysts cm −3 when sediment was collected in mid-October 2006. Germination experiments set up monthly had germination occur in all months when cysts were provided with adequate growth supporting conditions. Germination rates were highest in May and June when 100% germination occurred within 2 days. Longer incubation periods observed for the first two months of the study (November and December) may indicate a mandatory dormancy period of up to 5 months if the majority of cysts were deposited in the sediments following a late summer bloom that apparently occurred in Quartermaster Harbor in 2006 as indicated by Washington State Department of Health's toxin records. The data provide no evidence of an endogenous clock restricting germination to a specific annual timeframe for these shallow water cysts. This contrasts with the presence of a circannual endogenous clock, for deep water cysts of A. fundyense in the Gulf of Maine. The significance of these results is that germination of the A. catenella Puget Sound population appears to be primarily regulated by physiological requirements. However, once physiological requirements are met cysts can germinate rapidly, often within 24 h, when provided with adequate environmental conditions.