Carpet sea squirt

Carpet Sea-squirt (Didemnum vexillum) is a highly invasive non-native marine animal that could threaten conservation, fishing and the shellfish industry.

Reporting your sightings

If you think you have found carpet sea squirt, please email us at carpetseasquirt@snh.gov.uk or call 01463 725000 and tell us where and when you found it. If possible, take a digital photograph and attach this to your email.

There is also a poster available here.

What is the carpet sea squirt?

The carpet sea squirt belongs to a widespread group of marine creatures known as sea squirts. Some live a solo life but others, such as the carpet sea squirt, grow as a dense mass of individuals, forming a mat on underwater structures. While there are many species of native sea squirts that are harmless, the carpet sea squirt has spread around the world, causing both economic and environmental problems.

How to recognise the carpet sea squirt

The carpet sea squirt can be difficult to identify as it looks similar to some native species, but the following characteristics can help to identify it. The surface has a leathery texture (it is not slimy like other sea squirts) and has a noticeable veined surface. It has an orangey or mustard/tan colour which is fairly distinctive from native species. It can grow either as thin flexible sheets, often overgrowing other species, or in long rope-like growths. The GB Non-native Species Secretariat has produced an ID sheet to help identification.

Where is the carpet sea squirt found?

Thought to be originally from Japan, it has become a pest in other countries by smothering native species and interfering with fishing, aquaculture and other activities. Since 2008, it has been found in some marinas in England and Wales and there are strong concerns that it will spread more widely. Carpet sea squirt is most likely to spread by attaching itself to the hulls of boats or underwater structures such as pontoons that may be moved from place to place.

In October 2009, a colony was found in Largs on the Firth of Clyde - the first sighting in Scotland. Further surveys carried out in February 2010 did not find the sea squirt at other locations in the Firth of Clyde or Argyll.

Why is carpet sea squirt a problem?

The carpet sea squirt is a potential nuisance species that causes economic and environmental problems. It 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.

What is being done about carpet sea squirt in Scotland?

Since its initial discovery in Scotland in October 2009, further surveys have been carried out to see how widespread it has become. So far, it has only been found in Largs.

Top tips to help prevent its spread are as follows:

• 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.

See also The Green Blue advice for boat owners    and the Scottish Canoe Association advice to paddlers