Marine invader under monitoring

Scientists have developed a genetic tool to help environmental authorities monitor the spread and impact of Australia's most invasive marine species, the New Zealand screwshell.

The tool allows scientists to identify whether boating activities and shipping are contributing to the northerly spread of the screw shell up the east coast.

Beds of the introduced screwshell now cover an area greater than the size of Tasmania, with evidence it has out competed a native screwshell, Gazameda gunnii, on Tasmania's east coast. The New Zealand screwshell was unintentionally introduced in the 1920's and has now spread to the 80 metre depth contour of the continental shelf, occupying vast beds in waters off the eastern Victorian and NSW coasts as far north as Botany Bay.

"These new genetic technologies will provide authorities with a rapid assessment technique as a prelude to determining its impact on native flora and fauna, such as the commercial scallop beds of Bass Strait," says CSIRO's Dr Jawahar Patil. "More broadly, this is a tool that can be used to help protect Australia's coasts."

Last month an Intergovernmental Agreement was signed between the Australian Government, and the Tasmanian, Victorian and the Northern Territory Governments on a National System for the Prevention and Management of Marine Pest incursions.

The Agreement will ensure a coordinated approach to managing introduced pests that will involve all Government, industry, research and conservation stakeholders. However, environmental managers do not yet know whether they can control the further spread of the New Zealand screwshell, for example, by managing ships' ballast water.

CSIRO marine ecologist, Dr Nic Bax, says underwater surveys have clearly shown how widely this species is occupying the seafloor, dominating biodiversity and potentially impacting the habitat and food chain of commercial seafood species.

Larger and seemingly more dominant than the Australian screwshell, Maoriculpus has exhibited tolerance for a wide variety of water temperatures and depths.

Providing further research support, a joint program between CSIRO and the University of Tasmania is reviewing the introduced screwshell's preferred habitats, reproduction and feeding and impacts on native species and commercial scallops.

Prof Craig Johnson, University of Tasmania, says it is not uncommon to find accumulations of shells at densities of 2,000 per m2 of sea floor. Both alive and dead shells are likely to have significant impacts at these densities, particularly in areas where the majority of dead shells are occupied by hermit crabs.

Attempts to identify impacts on the native species drew little success with researchers having difficulty locating specimens in their research area. In September last year, the native Australian screw shell was listed as vulnerable under the Tasmanian Threatened Species Protection Act.

In a research project for the Commonwealth Department of Environment and Heritage, a team of geneticists and ecologists at CSIRO Marine Research led by Dr Patil has examined the screwshell's genetic makeup. The work was funded by the Natural Heritage Trust and CSIRO Marine Research.

A developed gene probe distinguishes the introduced screwshell from similar looking native species in seawater samples. Seawater samples taken in the Derwent were found to contain the screwshell larvae, indicating that it could be spread by shipping and other marine traffic.

Dr Patil says: "The genetic work is important in contributing to understanding the life cycle of the introduced screwshell and the way in which it spreads naturally or with human assistance. Until this work we did not know whether the introduced screwshell produced larvae that could be spread by the currents or larvae that always stayed on the seabed.

"Our approach will have additional application elsewhere as a tool in marine pest research conducted by environmental managers here and overseas."

Dr Patil and his team have previously developed genetic probes for three other introduced species, used in sampling the ballast water of ships to detect the presence of potential larval introductions of marine species from other regions.

Item provided courtesy of CSIRO