CYST AND RADIONUCLEOTIDE EVIDENCE FOR THE RECENT INTRODUCTION OF THE TOXIC DINOFLAGELLATE GYMNODINIUM-CATENATUM INTO TASMANIAN WATERS

Cysts of the dinoflagellate Gymnodinium catenatum were present only in the top sections of duplicate marine sediment cores from Deep Bay in southern Tasmania, Australia. Pb-210 and Cs-137 analyses indicate that the appearance of the cyst of this toxic dinoflagellate (one of the c ausative organisms of paralytic shellfish poisoning) occurred after 19 72. This sediment core evidence and the absence of this species from t he phytoplankton of most other neighbouring Australian waters suggest that Gymnodinium catenatum is not endemic to Tasmania but has been int roduced recently. This species was first seen in bloom proportions in Tasmania in 1980, with major blooms having occurred since then in 1986 , 1991 and 1993. Several lines of evidence suggest that, ballast water discharge from cargo vessels originating from Japan and South Korea, or less likely Europe, is the most probable mechanism of introduction.