Seabed invader threat to west coast fisheries

Published on Saturday 14 May 2011 18:13

A FEARED alien species which has caused serious damage to marine life across the globe is to be investigated by the Scottish Government.

Carpet sea squirt - didemnum vexillum - is spreading off Scotland's west coast, threatening lucrative shellfish farms and fishing grounds.

Categorised as a "highly invasive non-native marine animal" by Scottish Natural Heritage, its presence was first noticed at Largs marina in January last year. It is usually found in Japanese waters.

A study into possible measures to combat the sponge-like seabed feeder was advertised to academics this week, with options ranging from containment to eradication.

An ongoing outbreak in Holyhead, Wales, which began in 2008, has led to specialist divers being brought in to place massive bags around the harbour's structures, which interrupt the flow of nutrient-rich water the animal needs to thrive. The cost is estimated at around 200,000 a year.

In New Zealand its spread has been described as disastrous for the city of Picton, which is considering screening vessels and introducing tariffs to fund control measures.

Liz Cook, marine biology lecturer at the Scottish Association for Marine Science, said: "In New Zealand didemnum vexillum has been a major issue, particularly for farmers of shellfish and mussels.

"It forms a flat carpet on the sea floor which suffocates sea life. It covered the mussel lines and salmon cage netting and threatens to do that in Largs.

"Aquaculture on the west coast is extremely valuable and will be hit hard if it does spread out of the marina."