Carpet Tunicate, or didemnum vexillum, is a colonial tunicate which forms large tan, cream or orange sheet-like or lobed colonies which overgrow a variety of substrates as well as other organisms. Zooids (individuals) are about 1 to 2 mm in length and may have a spotted appearance. Carpet tunicate grows on a variety of man-made and natural hard substrates in the subtidal zone. Although it grows on rock or gravel it has not been observed to grow on mud or sand.
On Georges Bank (south-west of Nova Scotia) the Carpet Tunicate has overgrown an area of 250 km3 with coverage of 50 to 90 percent. This coverage is known to destroy the habitat of several species of fish, shellfish, and other bottom dwelling organisms. Like other colonial tunicate species the Carpet Tunicate can produce new colonies from fragments.
(Photo credit: Cawthron Institute, NZ)
Mean of introduction
Since eggs are fertilized within the matrix of the colony and larvae are only free-swimming for a few hours it is not likely that the species is spread through ballast water but it is more than likely it is spread through hull fouling. It has also been know to grow on the shells of shellfish and can be spread when the animal moves.
Management of the species
Fish and shellfish harvesters should avoid transferring harvested shellfish and fishing gear to other areas. Gear should be thoroughly dried before transfer. Boat hulls should be inspected and, if necessary, manually cleaned. Any organisms removed from boat hulls or gear should be disposed of on land. If pressure washing is necessary to remove colonial tunicates from equipment only do so on land and make sure the out-flow does not go into the sea, as colonies can regrow from small fragments. Report sightings by using the contact information on the main AIS page.