Colonial Tunicates

(Pancake batter tunicate (Didemnum vexillum), Golden star tunicate (Botryllus schlosseri), Violet tunicate (Botrylloides violaceous) and Compound sea squirt (Diplosoma listerianum)

What are They?

  • Colonial tunicates are invertebrate animals that grow in large groups to form a “colony”.
  • Colonies are made up of many microscopic tunicates (zooids) that often form rubbery mats that can cover almost anything underwater.
  • They can also form folds and lobes that hang down in the water.
  • Tunicates are also nicknamed “sea squirts” because they can squirt water out through their siphons.
Compound Sea Squirt
Compound sea squirt

Where did They Come From?

  • Tunicates may be carried on eelgrass, shellfish, boat hulls, motors, anchors, and fishing gear.
  • The pancake batter tunicate is thought to have originated in the Pacific Ocean near Japan.
  • The golden star tunicate is found throughout many regions of the world.
  • The violet tunicate originated in Asia.
  • The compound sea squirt is thought to have originated in northern Europe.

Where are They Now?

The pancake batter tunicate has invaded France, the Netherlands, Ireland, Scotland, Wales, New Zealand, the East Coast of North America (Georges Bank and New York north to Maine) and the west coast of North America from Alaska to California. The first record in eastern North America was in the Damariscotta River, Maine in 1983. Pancake batter was located in 2013 off Parrsboro, Nova Scotia in the Minas Basin and Fisheries and Oceans Canada is currently in the process of evaluating its presence.

Violet tunicate

The golden star tunicate has been reported in eastern Canada for several decades.

The violet tunicate was first observed in eastern Canada on the Atlantic coast of Nova Scotia in the 1990s; the Gulf of St. Lawrence in 2002; and the New Brunswick coast of the Bay of Fundy in 2009.

The compound sea squirt has spread along the American east coast. It was first observed in eastern Canada on the Magdalen Islands in 2008.


How did They get Their Names?

Pancake batter tunicate
Pancake batter tunicate

Didemnum vexillum often resembles “pancake batter poured over the seafloor”. Colonies can be white, beige, tan, pink, or orange sheets that look like pancake batter attached to animals, plants, and natural and artificial structures. Its colour, texture, and the appearance of it oozing and growing over organisms and structures have led to its name “pancake batter”.

The golden star tunicate is named from its daisy or star-like pattern formed by the zooids and sometimes golden in colour. It can also be orange, yellow, red, greenish-grey, violet, dark grey or black. The violet tunicate consists of individual zooids that are violet, whitish, yellow, orange, or reddish brown arranged like curving tracks.

The compound sea squirt forms dense colonies that are jelly-like (gelatinous) and see-through (translucent).

How/Where do They Live?

Golden star tunicate
Golden star tunicate

Adult colonial tunicates are usually found in sheltered areas and can grow on almost anything underwater. They may attach to rocky bottom, eelgrass, algae and shellfish as well as docks, floats, pilings, moorings, ropes, chains, ship hulls, and buoys. They can grow as sheets over the ocean bottom or whatever they are attached to.

Colonial tunicates reproduce by releasing sperm to fertilize eggs within the colony. These form into tadpole larvae that are released in the water. These tadpoles drift for a short time (minutes to hours), settle and form colonies. New colonies can also be produced when pieces break off and drift to a new area and become attached there.

What are the Effects on Native Species and Habitats, or Human Uses of the Ocean?

Colonial tunicates can change the number and types of plant, invertebrate and fish species in an area. They can smother both wild and farmed molluscs (blue mussels, quahogs, oysters, sea scallops). The tunicates feed on plankton (mi¬croscopic plants and animals), reducing the food available for other filter feeders. They can also prevent some species from settling to the ocean bottom in their early life stages and out-compete native species for space. Therefore, they are a great threat to biodiversity.

What can you do to Help?

Did you Know?

On the coast of Maine and Massachussetts, pancake batter tunicate has also been found on eelgrass. This concerns scientists because eelgrass is a habitat for the early life stages of shellfish and fish. The presence of the tunicate may not allow these species to survive there.

There are no effective ways to get rid of tunicates when they are established in an area. Sometimes even trying to remove a colonial tunicate may cause smaller pieces to break off, potentially begin¬ning new colonies. Preventing their spread into new areas is the best thing you can do. Know what these species look like and make sure any boating or diving gear is clean when moving from one area to another. Follow the general guidelines recommended by Fisheries and Oceans Canada on the weblink below.

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