Whilst Alexandrium blooms on the east coast of Tasmania and in New South Wales have caused abalone harvest closures in the past, until 2017 only low levels of paralytic shellfish toxins (PST) had been detected in abalone from these blooms (max. 0.3 mg STX.2HCl equiv/kg). This is in contrast to elevated levels of PST found during Gymnodinium blooms in southern Tasmania. However, during the 2017 bloom, abalone were found to exceed the bivalve regulatory limit at 1.2 mg STX equiv/kg.
A precautionary risk management approach has been taken to abalone harvest during Alexandrium blooms in Australia. The closure of abalone harvest zones is based on information arising from the bivalve shellfish monitoring program. The impact on the fishery on the east coast of Tasmania has been more than 25 block closures to date, some of which have been continuous for over 2 years. This conservative approach has been adopted due to both the paucity of information on PST accumulation in abalone from Alexandrium blooms, and the high consequence of any PST detection in overseas markets. Current testing costs are around $5,000 per site (minimum of 5 animals, two tissues, $500 per test), severely limiting the amount of testing that occurs.
This proposal has been developed to improve the risk management of PST in abalone, particularly to reduce the economic impact on fishers. It will also increase the understanding of the risk that Alexandrium species pose to accumulation of PST in abalone. It includes field and tank studies, with costs of the latter significantly offset by the biotoxin contamination facility that will operate at Roseworthy between March and September 2018, funded through an Australian Seafood CRC grant .
Final report
The accumulation of paralytic shellfish toxins (PST) of microalgal origin in abalone tissues causes a trade and human health risk that requires active management. Toxic algal blooms of the genus Alexandrium have recently caused several abalone harvest closures on the east coast of Australia. Risk management is hampered by a scarcity of knowledge on the mechanisms and rates of accumulation and depuration of the associated PST. A collaborative effort by researchers from the South Australian Research and Development Institute (SARDI), the Institute of Marine and Antarctic Science (IMAS) and Cawthron Institute conducted field studies on the east coast of Tasmania during toxic blooms in 2018 and 2019, and experimental studies in South Australia in 2018 to investigate uptake and depuration of PST from A. catenella in Haliotis rubra rubra, Blacklip Abalone. Several key results from the study will be used to inform improved risk management of this issue. In particular, we showed for the first time that: abalone can accumulate PST from exposure to toxic algal cells; the predominant accumulation is in the foot tissue; and toxins depurate extremely slowly from this tissue. We conducted a successful laboratory validation of a rapid screening test for PST analysis in foot tissue for future use during A. catenella blooms that should lead to significant savings in PST monitoring in Tasmania.
