Alexandrium tamarense blooms and shellfish toxicity along Tasmania's eastern coast

In October 2012, paralytic shellfish toxin (PST) contamination was detected along the east coast of Tasmania resulting in closure of 350klm of coastline to harvest of mussels, oysters, scallops, wild lobster and abalone. Closures persisted for up to six months resulting in an estimated economic loss of over $23M. Collaborative effort by regulators and researchers established the causative organism as <i>Alexandrium tamarense</i>, a species that is widespread across south-eastern Australia but never previously linked to shellfish toxicity in Australia. Bloom populations and toxicity emerged again in August 2013 resulting in widespread harvest closures, contamination of benthic fisheries and detection of PST toxicity in scallops as far north as Flinders Island. Studies of cultures from both 2012 and 2013 confirmed <i>A. tamarense</i> Group 1 as a major source of PST, producing a PST profile dominated by Cl/2 and GTXl/4, low proportions of NEO, C3/4, and traces of GTX2/3 and dcGTX2/3, but considerable (3-10 fold) variation in STX content and toxicity (STX eq./cell). However, DNA sequences matching <i>A. catenella</i> Type 4, were also recovered from both seawater and shellfish, indicating blooms contained multiple genotypes of differing toxicity. The scale and evident spatial/genetic variation presents a highly complex monitoring challenge for both regulators and researchers.