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Carpet Sea Squirt Survey

Monitoring of alien species: the carpet sea squirt survey

The carpet sea squirt (Didemnum vexillum) is a highly invasive species, listed on Defra’s non-native species ‘Alert’ list. Originally from Japan, it first appeared in the UK in 2008 and is transported in ballast water or on the hull of commercial and recreational vessels. Didemnum vexillum grows on hard surfaces such as rock, reef, marina structures or shell and it spreads rapidly, creating a carpet of sea squirts which can reduce biodiversity and negatively impact shellfish fisheries.

Previous intertidal surveys showed an increase in Didemnum vexillum over the past few years on the north Kent coast. At the beginning of 2013 KEIFCA undertook a survey for Natural England looking for a subtidal source of Didemnum vexillum. Underwater video footage was collected using our Video Ray Pro3 ROV (remote operated vehicle) at five sites across the north Kent coast. Eighteen videos were analysed for the presence of Didemnum vexillum in sand, mud, rock and chalk habitats.

Didemnum vexillum was not observed in any of the five subtidal sites. This data will be added to a national database of invasive species sightings.