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Shellfish toxin study reveals the impact of warmer waters

Posted June 8, 2015

A collaboration between UTS scientists and the NSW Government is addressing, for the first time, the influence of rising ocean temperatures on the uptake of highly potent neurotoxins in commercially important shellfish species.

Picture by Dr Hazel Farrell

Picture by Dr Hazel Farrell

These naturally occurring toxins, known collectively as PSTs (Paralytic Shellfish Toxin) are produced by certain species of microalgae and accumulate in filter feeding shellfish such as oysters, posing a threat to human health if consumed. The NSW Food Authority (NSWFA) is supporting the research as part of a broader, ongoing environmental monitoring program of shellfish operations along the entire NSW coast.

The results of the study, published in Global Change Biology, give scientists and aquaculture managers an increased understanding of how different species within the same harvest area could respond to toxin exposure and environmental stress associated with climate change, in this case increasing temperatures. The study highlights the complexities of PST metabolism in oysters and the resultant risk management decisions that must be made when algal blooms occur in harvest areas.

The study is timely. Worldwide, warmer waters are resulting in an increase in the frequency and intensity of algal blooms, threatening not only human health but also the viability of economically important  aquaculture industries at a time of rising demand for high quality seafood.

Lead author Dr Hazel Farrell, NSWFA scientist and Associate of UTS, said that this investigation is particularly relevant to NSW.

“The metabolism of shellfish is temperature dependent and increases in ocean temperature may influence both the abundance and distribution of Alexandrium and the dynamics of toxin uptake,” she said.

“NSW is considered a ‘hotspot’ for seawater temperature increases. It’s crucial to understand factors affecting accumulation of biotoxins in shellfish so we can design the right management strategies that take into account species-specific effects associated with environmental change.”

The research team conducted a large-scale feeding experiment at the DPI Port Stephens Fisheries Institute on the native Sydney rock oyster, and both diploid and triploid forms of the Pacific oyster, at two temperatures to reflect current and predicted climate scenarios. The oysters were exposed to a toxic diet of the PST producer Alexandrium minutum, and the uptake, accumulation and detoxification of the biotoxins was measured, along with the metabolic response of the oysters. A comparison was then made with oysters that received a non-toxic diet.

Associate Professor Shauna Murray leads the Seafood Safety research program in the Plant Functional Biology and Climate Change Cluster at UTS. An expert in evolution and molecular ecology of toxin producing marine algae and Chief Investigator on the study she explains that previous feeding experiments didn’t investigate multiple species at different temperatures.

“Our experiment examined three different oyster types and found that two of the three oyster types (Sydney rock and diploid Pacific) accumulated less toxin at higher temperatures,” she said.

“However, we also found the toxin removal process to be slower at warmer temperatures. This is a complex scenario for management strategies, particularly if PST events become more frequent and intense in the future. This research arms us with the knowledge needed to deal with future environmental changes, supporting an eminently sustainable industry and protecting public health.”

The research team plan to conduct sampling during a PST bloom event to determine if the variations between species are similar in the field. During bloom events harvest areas typically undergo mandatory closures which can cause economic hardship.

“Our results indicate that in harvest areas where multiple species are cultivated, pending biotoxin testing outcomes, there is potential to restrict shellfish harvest closures to a particular species rather than the entire stock during bloom events,” Dr Farrell said.

Source: UTS

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