This project will assess whether sea urchins are able to accumulate PST in a series of aquaculture trials exposing urchins to bulk cultured toxic algal species. These trials have been designed to provide answers to key questions that arose during the previously conducted risk profile, and that need to be addressed to conclusively determine if Australian sea urchins are at risk of PST uptake and whether ongoing biotoxin monitoring is warranted:
Does the risk of PST uptake differ between sea urchin species?
We will be including both Longspined and Shortspined Urchins in our exposures to determine if the risk of PST uptake differs between these species. Overseas evidence suggests that this may well be the case; during a large Alexandrium bloom in Chilean waters, one urchin species presented with PST levels exceeding the threshold considered safe for human consumption, while another species collected right next to it did not contain any PST.
Does the risk differ between PST producing algal species?
Sea urchins will be exposed to two different types of PST producing algae belonging to the genera Gymnodinium and Alexandrium. Both of these are commonly encountered in Australian waters and are known for producing different relative amounts of various PST analogues. We know from experiences with Abalone in Tasmania that rates of biotoxin uptake and depuration can differ substantially between these toxic species, and it remains to be seen whether this also holds true for sea urchins as fellow grazers. From our previously conducted field sampling, we anticipate the risk of PST uptake to be low during low to moderate Alexandrium blooms, but could not provide DAFF with any statements about high density blooms due to limited field data. The only urchin sample collected during a Gymnodinium bloom did however contain elevated PST levels. By running exposures with both these key PST producing algal species, we will investigate any potential differences in PST uptake between these two species.
If there is toxin uptake, where in the urchin does it accumulate?
Determining where in the urchin PST accumulates will be critical to comparing and ranking Australian PST risk relative to overseas observations. There are several studies showing PST uptake in urchins from the North Sea, Madeira and Chile, but it remains unknown whether these toxins were present in the viscera or the roe, as the entire urchin test content was analysed. We will be analysing both tissues separately, to ensure that our assessment reflects PST uptake risk in the roe as the commercially marketed product, as well as in the viscera if the product is exported whole/live.
The answers to these questions, together with the already conducted PST risk profile, will be used to determine whether there is any risk of PST uptake by Australian sea urchins. Tasmania is not the only state where blooms of harmful algal species have been recurring, and results will be communicated to fisheries and seafood safety managers in other jurisdictions to ensure that biotoxin testing of Australian sea urchins is commensurate to risk. This is not only an important measure to inform food safety and balance the cost burden to industry, it is particularly critical to support the rapidly developing Centrostephanus rodgersii industry which is being used as a reef protection and restoration tool in areas where the species is range-extended and overpopulated; informed and consistent management of risks to Australian sea urchin branding and marketability are key.
