Carpet sea squirt

Didemnum vexillum


Photo credit: ©Julia Nunn

  • Marine hard surfaces. The colonies have been found at water depths ranging from intertidal to continental shelf depths of 65m (213 ft).

  • Exact identification of this species is very difficult and can only be undertaken by a trained expert. However, in general native species are not found in large colonies and do not form the candlewax-like dripping structures, as seen in the photographs. Please see the Habitas website on Sponges of Britain and Ireland for more info on native species.
  • The invasive form can be describes as long, ropey or beard-like hanging from hard surfaces such as docks, aquaculture facilities, and ship hulls, or may be found as extensive mats covering rocky sea beds (pebbles, cobbles, boulders, and rock outcrops).
  • It can reproduce from fragments and can complete a generation cycle within a week.

Download N.I.E.A. ID guide

Origin and Distribution:
  • Uncertain at present.
  • The species is known from The Netherlands and France in Europe while worldwide the species is now recognised in Asia, Australasia-Pacific, Europe, and North America.

  • Alter marine habitats.
  • Interfere with fishing, aquaculture, and other coastal and offshore activities.
  • Increased fouling of manmade structures such as docks, moorings, and boat hulls.
  • Overgrow other organisms such seaweed, scallops, mussels, and oysters that depend on the seafloor for habitat.
  • May impact on underwater archaeological sites such as ship wrecks. Produce noxious substances that deter most fish and other animals.

How did it get here?
  • Uncertain at present.
  • Likely vector is fouling of ocean going vessel and/or contamination of aquacultre produce.

Is it found in Northern Ireland?
  • It is present in Northern Ireland. The species was recorded in Strangford Lough, County Down (NI) during October 2012.
  • More distribution information can be seen on the NBN Atlas NI.

You can help by reporting any sightings: @ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
Further Resources:
Prevent Spread:
  • Prevent fouling of boats and equipment.
  • Clean all equipment including boats before moving to new waterbodies.
  • Report all sightings.
For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email:

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland