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 est uarine waters (temperature range 13-25 degrees C). Cysts produced by c ultured isolates exhibited dormancy periods at 17 degrees C as short a s 28-55 days. This contrasts with the usually longer dormancy requirem ents of temperate populations of A. catenella from Japan (97 days at 2 3 degrees C) and of A. tamarense from Cape Cod or British Columbia. Wi th some Australian cysts, a l-h temperature increase from 17 degrees t o 25 degrees C (equivalent to summer heating of shallow estuaries) imp roved germination success (up to 100% germination achieved after 98 da ys), but cold-dark storage did not produce the lengthened dormancy req uirements 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 differen t cyst dormancy requirements which play different ecological roles (ov erwintering strategy v. rapid cycling between benthos and plankton).