CCW tackles invasive sea squirt in Holyhead harbour

The Countryside Council for Wales has started work to eradicate an invasive sea squirt in Holyhead harbour, which is threatening to smother native marine life in Wales.

the alien invader...carpet seasquirt
Photo by Ronan Holt©CCW

The carpet sea squirt (Didemnum vexillum), which originates from Japan, has established itself on the marina’s floating pontoons and mooring chains and mooring buoys in the harbour.

If left unchecked, it could spread rapidly, colonising natural habitats and threatening the important mussel industry in the Menai Strait.

The carpet sea squirt has had devastating impact on marine life in other parts of the world where it has been accidentally introduced, such as New Zealand.

There, it has literally carpeted acres of sea bed, making these areas unsuitable for native marine plants and animals.

The sea squirt was most likely brought into Holyhead harbour on the hulls of leisure craft. The Countryside Council for Wales made a pilot attempt to clear the seasquirt in the winter 2009. Now, building on this experience, CCW’s marine staff will be working intensively to completely eradicate the creature.

The work involves fixing massive bags around the underwater structures of the marina. By stopping clean flows of water from reaching the sea squirts, they will suffocate and die. If eradication techniques are successful here, CCW could advise other affected areas in the UK on how to get rid of the species.

The owners of Holyhead Marina are supporting CCW’s efforts. The target is to completely rid the harbour of sea squirt by spring 2012 before it can spread more rapidly in the spring and summer.

Diver fixes massive bag to smother the invasive seasquirt-Holyhead marina. Photo by Ronan Holt©CCW

Rohan Holt, CCW marine biologist managing the project said: “If we successfully eradicate the sea squirt, we will work hard to make sure that it does not recolonise. This will mean careful monitoring in Holyhead marina and other marinas and popular mooring areas throughout Wales to check that it hasn’t reappeared.

“Guidelines for small boat owners on how they can help will be an important part of this, as well as regular checks.”

Have you seen this creature?

• Didemnum vexillum is a spongy textured sea squirt with a leathery feel. It does not feel slimy.
• It is a distinctive mustard or pale orangey/yellow or beige colour;
• It often appears like pale flat patches or wax dripping from artificial structures just below water level;
• Its surface has leaf-like veins with tiny pores.

This project is funded by the Welsh Government.

Contact the Countryside Council for Wales’ Enquiry Unit for more information on:
0845 1306229.

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NOTES TO EDITORS

For further information, please contact Helen Evans, CCW PR Officer on 01248 387377 or 07717225589. h.evans@ccw.gov.uk; or Brân Devey on 02920 772 403; 07747767443 or bran.devey@ccw.gov.uk .

The Countryside Council for Wales is a Welsh Government Sponsored Body, working for a better Wales where everyone values and cares for our natural environment. More information about our work is available on www.ccw.gov.uk