Short cyst-dormancy period of an Australian isolate of the toxic dinoflagellate Alexandrium catenella

Cyst beds of Alexandrium catenella (a causative organism of Paralytic Shellfish Poisoning) are widespread in New South Wales coastal and estuarine waters (temperature range 13-25 degrees C). Cysts produced by cultured isolates exhibited dormancy periods at 17 degrees C as short as 28-55 days. This contrasts with the usually longer dormancy requirements of temperate populations of A. catenella from Japan (97 days at 23 degrees C) and of A. tamarense from Cape Cod or British Columbia. With some Australian cysts, a l-h temperature increase from 17 degrees to 25 degrees C (equivalent to summer heating of shallow estuaries) improved germination success (up to 100% germination achieved after 98 days), but cold-dark storage did not produce the lengthened dormancy requirements that have been reported overseas for overwintering temperate cyst populations. The significance of this finding is that different geographic isolates of the same dinoflagellate taxon can have different cyst dormancy requirements which play different ecological roles (overwintering strategy v. rapid cycling between benthos and plankton).