Carpet sea squirts (Didemnum vexillum) from Japan are moving around the world, presumably hitching rides on boats. In the UK there are currently nine known sites from the Solent to the Clyde, including Holyhead Marina. But Holyhead is the only site where pioneering action is being taken, by the Countryside Council for Wales, to repel the invasion.
They are bad news for our native species, likely to out-compete and smother them in a colonial carpet, hence the name carpet sea squirt. The commercial catalyst for taking action at Holyhead is the proximity and threat to the rich mussel beds of the Menai Strait from which five times the annual UK consumption is exported.
|Leathery piece of carpet sea squirt|
Considerable work has been done over the past couple of years to eradicate the squirts and I recently met up with the team of eight divers surveying the marina. The good news is that the vast majority of the squirts have been killed off with just a few surviving patches confined to chains that anchor the pontoons to the ocean floor.
The next step is to treat the chains before this season’s larvae are released and this will involve wrapping 150 chains in polythene and bleach. Typically the chains are about five metres long and the bleach powder will be packed into socks – about three socks per chain. So, if you are serving at a shop where someone approaches with a trolley of 225 pairs of socks, you will know that it’s not some sort of fetish but conservation in action.