How would you be feeling, if you had parked your boat in the marina at Caergybi (Holyhead) just off Ynys Môn (Anglesey, see map below)


and found its anchor chains covered with this?


 
This is Didemnum vexillum, a ferociously invasive sea squirt from Japan.  Some tunicates are quite pretty, but this one is particularly unprepossessing.  Carried by ocean-going vessels, this carpet sea squirt has turned up in temperate waters from British Columbia to New Zealand, pushing aside native species, and is now threatening the mussel beds of North Wales.
 
As this US Government page shows, it gets everywhere and covers everything.  The Countryside Council for Wales is on the case, too.
 
And this evening we saw Miranda Krestovnikoff, zoologist, diver and BBC television presenter, accompanying a local diver as he wrapped the fouled anchor chains in plastic sheet.  This should starve the carpet sea squirts which filter their food from the currents, alas along with them taking out other marine life including the native British sea squirts, but these latter should re-colonize the area next season.
 
From now on, constant vigilance!