Botrylloides giganteum - non-native seasquirt

Sea squirt - is it native, or non native? A case study discussing the challenges faced by relevant authorities in identifying and managing the threat of introduced marine pest species.

In late 2018, NSW Department of Primary Industries Aquatic Biosecurity began investigating a public report regarding the suspicion of the presence of a marine pest of concern Didemnum vexillum in areas of Sydney. Multiple samples were collected by DPI Fisheries experts during the investigation which raised concerns that the species was both highly abundant and through initial observation of its appearance, looked like a different non-native marine ascidian, Botrylloides giganteum not previously detected in NSW.

Samples sent to DPIs Elizabeth Macarthur Agricultural Institute (EMAI) for identification (through DNA analysis) excluded both D. vexillum and although raised as a potential concern, diagnostic capability did not allow B. giganteum to be excluded or identified. This left NSW DPI not knowing the identification of what was being observed as a highly fouling and highly abundant marine ascidian species in a high boating traffic area of Georges River.

To try to find out more, additional samples were collected by DPI Fisheries and through consultation with an international ascidian expert, were submitted to a Queensland laboratory for preliminary identification.

On Monday 18 March 2019, NSW DPI Aquatic Biosecurity received preliminary identification advice from the Queensland laboratory of Botrylloides giganteum (Sea Squirt), from a sample taken from the Botany Bay area. These results were confirmed using DNA analysis through the Departments EMAI laboratory.

More samples have been collected to support further investigation into this new non-native marine species found in Georges River. These samples will be utilised to provide further information on the abundance of the non-native marine ascidian, as well as to support the development of further DNA analysis techniques and improved surveillance and diagnostic tools for such species into the future.

Non-native marine ascidians can look similar to native marine ascidians and it is almost impossible to identify these types of species in the field using technologies currently available. To prevent the introduction and spread of such species, we all need to be vigilant and take steps to minimise the chances of introducing new species. ‘Make ‘clean’ part of your routine