Monitoring under scrutiny in wake of algal outbreak

By Catherine Norwood

More than 200 leading international shellfish safety specialists gathered in Sydney for the 9th International Conference on Molluscan Shellfish Safety in March this year to discuss the latest industry research, management and policy issues.

Co-chair of the conference Gustaaf Hallegraeff from the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS) says a diverse range of quality assurance, disease and toxicity issues were discussed, with almost 100 presentations at the conference.

Several presentations related to algae and the risk of accumulated toxins continues to grow, he says, as this becomes an increasingly significant issue for the industry.

“When the biennial conference was first held almost 20 years ago there were only one or two papers on algal issues. At this year’s event, these represented about half the conference program,” he says.

This included the opening keynote presentation from CSIRO’s Anthony Richardson on marine plankton and climate change and a panel discussion on the 2012 toxic algal outbreak off Tasmania’s east coast.

Global trend

Gustaaf Hallegraeff says the Tasmanian outbreak is part of a global pattern, with hazardous blooms occurring in new locations and caused by algae species that had not previously been problematic.

The Tasmanian outbreak of the toxic dinoflagellate Alexandrium algae during October 2012 was unprecedented and affected more than 200 kilometres of Tasmania’s coastline. Shellfish accumulate toxins as they feed on the algae, which can make them dangerous, and potentially fatal, to eat.

The algal bloom resulted in widespread closures of commercial and recreational bivalve growing areas. Rocklobster, scallop, abalone and crab fisheries were also temporarily closed.

As chair of the panel discussion, Gustaaf Hallegraeff says many aspects of the Tasmanian algal outbreak were handled well.

These included public and industry communication, availability of biotoxin testing facilities in Sydney and recall procedures implemented by the businesses involved.

There were no confirmed cases of illness linked to the outbreak and more than 10,000 tonnes of potentially affected mussels were recalled from around Australia and overseas.

The most embarrassing aspect of the incident was that the alarm was first raised by the Japanese import testing system, Gustaaf Hallegraeff says. Japan identified levels of paralytic shellfish toxins (PST) in mussel meat from Spring Bay, Tasmania, that exceeded both Japanese and Australian health safety standards. This was later confirmed by testing in Australia.

The workshop identified inexperience with the Alexandrium species involved, monitoring schedules, delays in testing algal samples and an initial misidentification of the species as critical issues to be addressed.

Gustaaf Hallegraeff says it appears that the toxic bloom affected most of the east coast of Tasmania simultaneously, rather than seeding from one region to the next.

The peak of the bloom was missed in fortnightly algal monitoring that the Tasmanian Shellfish Quality Assurance Program had in place.

This frequency was based on the east-coast aquaculture zone being classed as a ‘medium-risk’ region.

Exports halted

The outbreak resulted in the suspension of all Australian bivalve exports for a brief time, until it could be confirmed that only Tasmanian products were affected. The total economic loss to the affected fisheries has been estimated at $12 million.

The Japanese market remains closed to Tasmanian mussel imports – requiring 100-per-cent, on-arrival testing for PST, a requirement that will remain in place for at least two years after the outbreak.

Much of the focus of the event has been on mussels and exports; however, additional monitoring found “unacceptably high concentrations of toxins in other biota off the east coast of Tasmania”, Gustaaf Hallegraeff says.

He says there was limited knowledge and experience in dealing with Alexandrium outbreaks in the Spring Bay area where the outbreak was first identified. Prior to 2012, there had been one Alexandrium catenella bloom in the aquaculture zone on Tasmania’s east coast. The related Alexandrium tamarense responsible for the 2012 contamination had not previously been identified in bloom proportions in the region.

“Even with years of experience it is extremely difficult to identify these species from similar non-toxic ones by microscopic analysis. And while rapid DNA testing has been developed, this was not used by the laboratory responsible for processing of the samples,” Gustaaf Hallegraeff says.

Information from the 2012 outbreak and a subsequent algal bloom have provided a greater understanding of how cell counts correlate with toxicity levels in shellfish. Mussels are perhaps the most sensitive species, based on meat tests during periods of high cell counts.

Gustaaf Hallegraeff says the algal bloom affected all of the shellfish growing areas on the east coast. Scallops, rocklobsters and giant crabs from depths to 300 metres off St Helens in north-east Tasmania were found to contain toxins. Other species tested and found to be unaffected included abalone, periwinkle, flathead, sea urchins, squid and Banded Morwong.

He says the bloom has created a paradigm shift in biotoxin management in Tasmania. The risk rating for hazardous algal blooms has been upgraded from medium to high, which will require increased levels of monitoring and testing.

The toxic nature of the species, widespread potential distribution of the algae from an offshore source and the high likelihood that cyst beds for the species have now been established have all contributed to the revised risk rating. 

More information

Gustaaf Hallegraeff, gustaaf.hallegraeff@utas.edu.au