Preventing a marine invasion in the subantarctic

The Mediterranean mussel Mytilus galloprovincialis in the sea chests of the S.A. Agulhas.
The Mediterranean mussel Mytilus galloprovincialis in the sea chests of the S.A. Agulhas. (Photo Jennifer Lee)
A remotely operated video called a videoray.The South African Antarctic resupply vessel S.A. Agulhas. Fouling communities observed on the hull of the S.A. Agulhas

As the climate warms and visitors to the Antarctic and subantarctic increase, the threat of an invasion by marine species, carried to the region on resupply vessels and tourist ships is increasing.

Speaking at The Third International Forum on the Sub-Antarctic, Dr Jennifer Lee, a post-doctoral fellow at the Centre for Invasion Biology, Stellenbosch University, South Africa, said preventative action was essential.

‘It’s difficult, expensive and sometimes impossible to eradicate species in a terrestrial habitat and there’s never been a successful eradication in a marine habitat,’ she said. ‘There is no cure; prevention really is the only way.’

Dr Lee and her colleagues, in association with the South African National Antarctic program, investigated the risks of transporting alien species into the subantarctic by the two most likely means – on ships’ hulls and in sea chests.

The team examined the development of hull-fouling communities on the South African resupply vessel S.A. Agulhas by surveying the ship’s hull before and after every voyage over two years, using a remotely operated vehicle fitted with a moveable camera and lights. The team divided the hull into 10 two metre-wide transects, four metres apart, and took continuous video footage over these transects. They observed a range of organisms taking up residence, including various types of algae, small crustaceans, sea squirts and mussels.

‘The most profound impact on fouling of the hull occurred after the vessel travelled through sea ice. It went from having about 11% fouling cover to zero. So the risk of transporting species into the Antarctic was very low,’ Dr Lee said.

‘But the sea ice removed the anti-fouling coating from the ship’s hull, which enabled a more rapid accumulation of organisms when the vessel was in port. Then, when the vessel travelled through the open ocean, almost intact communities were transported from Cape Town to the subantarctic islands.’

The team was also shocked to discover the favourable living conditions provided by sea chests. These covered recesses into ships’ hulls, where water is taken onboard for engine cooling, have a constant flow of water through them and are protected from heavy seas and ice scour.

‘The sea chest of the Agulhas was full of a globally invasive bivalve species, the Mediterranean mussel (Mytilus galloprovincialis), many samples of which were over two years old. This means they had survived transport to Gough and Marion islands and to colder waters in Antarctica,’ Dr Lee said.

A review of the scientific literature indicated that most of the organisms present on the Agulhas’ hull or in its sea chest were physiologically capable of surviving in the subantarctic environment, and some in even colder water. However Dr Lee said more information on the temperature tolerance of a wider range of fouling species was required before a full risk assessment could be made.

More information is also needed on how vessel type and size affects hull fouling.

‘Most research has been done on medium-sized research ships but small yachts and larger tourist ships could be affected differently,’ she said.

‘And we don’t know how the species composition of the home port affects the fouling community composition. Most work on this has been done in Australia or South Africa, but many vessels leave from Ushuaia in South America.’

Dr Lee said new technologies promised to provide cost-effective strategies for dealing with hull fouling, such as the Hull Identification System for Marine Autonomous Robots. The ‘HISMAR’ attaches magnetically to ships’ hulls and removes light to medium fouling using high pressure water jets. This water is filtered of biological and chemical contaminants before release.

‘This sort of technology may be less expensive and time consuming than frequent dry docking or using divers to clean the hull,’ Dr Lee said.

‘By adopting a more precautionary approach to hull fouling we can reduce the threat of a subantarctic marine invasion while further research is conducted to better define the risks.’

WENDY PYPER

Australian Antarctic Division

More information

J. E. Lee and S. L. Chown. Temporal development of hull-fouling assemblages associated with an Antarctic supply vessel. Marine Ecology Progress Series 386: 97-105, 2009.