Alexandrium tamarense Group I as the cause of PST on the east coast of Tasmania, Australia

In October 2012 paralytic shellfish toxins (PST) were detected in shellfish on Tasmania's east coast resulting in widespread harvest closures of mussels, oysters, scallops, rock lobster and abalone over a period of six months along 350 km of coastline with total economic losses estimated at $23M. Phytoplankton sampling indicated Alexandrium tamarense as the likely source, a species not previously linked to PST in Australia because past recorded blooms were low-toxicity A. tamarense Group 5. More than 20 cultures were established from inshore and the continental shelf-edge locations. DNA sequence analysis (LSU-rDNA, rONA-ITS, STX synthetase SxtA1/A4) confirmed all isolates as toxic A. tamarense Group I, not previously known from Australasia. HPLC fluorescence analysis of PST showed a consistent profile dominated by C1/2 and GTX1/4, low proportions of NEO, C3/4, and traces of GTX2/3 and dcGTX2/3, with an 8-fold variation in STX content (8-65 fmol cell ^-1) among strains. Sequences of A. catenella Group IV were also recovered from seawater and shellfish samples indicating that multiple toxic Alexandrium genotypes may have contributed to the 2012 event. Cells of A. tamarense were detected again in early July 2013 resulting in widespread PST from Flinders Island (Bass Strait) and south to the Tasman Peninsula during winter-spring. The presence of G. catenatum and now at least three A. tamarense genotypes extend PST risk in Tasmania to year-round, presenting a major challenge for Tasmanian seafood assurance and HAB monitoring.