EARLY WARNING OF TOXIC DINOFLAGELLATE BLOOMS OF GYMNODINIUM-CATENATUMIN SOUTHERN TASMANIAN WATERS

Blooms of the toxic dinoflagellate Gymnodinium catenatum (a causative organism of paralytic shellfish poisoning) in the Derwent and Huon est uaries of southern Tasmania, Australia, are predictable, annually recu rrent events in the period January to June (late summer to early winte r). However, their spatial distribution, duration and magnitude exhibi t significant interannual variability. High shellfish toxicities in 19 86, 1991 and 1993 (>8000 mu g paralytic shellfish poisoning per 100 g shellfish meat) also coincided with the greatest spatial extent of she llfish toxicity (up to 35 shellfish farms closed for periods up to 6 m onths). An exploratory analysis of the results of a shellfish toxin mo nitoring programme conducted from 1986 to 1994, and of available hydro logical and meteorological data for the region, indicates that a signi ficant G. catenatum bloom in Tasmanian waters can only develop within a permissive seasonal water temperature window (>14 degrees C at the t ime of bloom initiation) requiring a rainfall event as a trigger (Huon River discharge, measured at Frying Pan Creek, must exceed 100 000 me galitres over a 3-week period) and a calm stable water column for sust ained development (windspeed <5 m s(-1) for periods of 5 days or more) . Once established, dinoflagellate populations are subject to disturba nce by turbulence caused by high windstress; this explains the inciden ce in some years of multiple shellfish toxicity peaks. In winter month s declining water temperatures (<10 degrees C) and increasing windstre ss are responsible for the termination of seasonal dinoflagellate bloo ms.