Warning: invasive carpet sea squirt hits Clyde and Argyll coasts

It may look like the results of a night’s binge drinking but it’s a non-native invasion this time.

A small colony of the invasive carpet sea squirt (Didemnum vexillum) has been found in the Firth of Clyde.

Surveys of marinas in the Firth of Clyde and on the Argyll coast will be carried out from late January by Argyll’s  Scottish Association for Marine Science (SAMS) to discover how widespread it has become. Funded by Scottish Natural Heritage (SNH) and Marine Scotland, the information gathered will help decide how the species should be dealt with.

Meanwhile boat owners are being asked to make extra efforts to keep boat hulls clean and free of fouling to help prevent its spread.

The colony was spotted at Largs Yacht Haven by Chris Beveridge of Scottish Association of Marine Sciences (SAMS), during a routine survey, first on a mussell, then on mooring lines.

She says: ‘This is one of our target species, so when I spotted a mussel on a pontoon, covered with a fawn coloured growth, I immediately suspected the invasive sea squirt.

‘We carry out surveys of west coast marinas every year, on the lookout for a variety of non-native species that have the potential to reach Scotland. The sea squirt may have been brought into Largs Yacht Haven on the hulls of leisure craft which have travelled from Wales or Ireland, where it is already established. It could be a real menace for all users of the marine environment if it spreads up the coast. This could have considerable negative economic impact’.

Scottish Natural Heritage’s (SNH) Dr David Donnan, explains: ‘The carpet sea squirt can reproduce and spread rapidly and tends to smother other marine life that grows on the seabed. It is especially good at growing over underwater structures such as aquaculture equipment, boat hulls and pontoons. It has spread around the world although it is thought to have originally come from Japan.

‘Experience from Canada, New Zealand, continental Europe and Ireland has highlighted it as a potential nuisance species that causes economic and environmental problems. The removal of the large, gelatinous growths can be difficult and costly.

‘We have been on the lookout for this species in Scotland as it was found in Holyhead Harbour in North Wales in 2008 and more recently in the south of England. This recent finding in Largs Yacht Haven is the first sighting in Scotland’.

What it looks like and what to check

Carpet sea squirt is most likely to spread by attaching itself to the hulls of boats.

It is a distinctive mustard, pale orangey-yellow or beige colour and often appears as pale flat patches. Larger growths may look like wax dripping from artificial structures just below water level. Its surface has leaf-like veins with tiny pores and it has a spongy texture and a leathery feel to it.

David Donnan added: “It can be quite tricky to identify but top tips to help prevent its spread are:

• Keep hulls of boats clean, free of fouling and treated with anti-fouling paint
• When hulls are cleaned make use of a closed-loop or filtered wash down facility and/or steam clean
• Clean fishing gear and other equipment on a regular basis
• Dispose of any fouling including weed carefully so that it doesn’t go back into the water.

You can find out more, including an identification sheet, by visiting the Non Native Species website from 1st February onwards.

A poster has also been produced to alert the public to the carpet sea squirt – it will be sent to marinas in Scotland and across the rest of Britain in the near future.

For more information on the carpet sea squirt contact David Donnan

• by phone: on 01738 458664
• by email: david.donnan@snh.gov.uk

For more information on potential aquaculture impacts of the carpet sea squirt contact  Dr Kenny Black of the Scottish Association for Marine Science

• by phone: on 01631 559259/559342
• by email: kenny.black@sams.ac.uk

The photographs above of carpet sea squirt are from copyright holder, Scottish Association of Marie Science and may not be reproduced without permission.