Unwelcome arrival of invasive sea squirt in Scottish seas

Marinas in the Firth of Clyde and on the Argyll coast are to be surveyed by
marine scientists following the discovery of another invasive non-native species
in Scottish waters.

A small colony of the invasive carpet sea squirt (Didemnum vexillum) has been
found in the Firth of Clyde. Surveys will be carried out from late January by
the Scottish Association for Marine Science (SAMS) to investigate 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.

Dr David Donnan, policy and advice manager at SNH explained: “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.”

Chris Beveridge of SAMS spotted the small colony of what she suspected to be
the carpet sea squirt during a routine survey. She said: “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.”

She later found a larger colony on the marina’s mooring lines. She added:
“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, with considerable economic impact."

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 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.

“People can find out more, including an identification sheet, by visiting the
website www.nonnativespecies.org from 1 February. 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 call David Donnan on 01738 458664
or email david.donnan@snh.gov.uk For more information on potential aquaculture
impacts of the carpet sea squirt call Dr Kenny Black, Scottish Association for
Marine Science on 01631 559259/559342 or email kenny.black@sams.ac.uk