Solitary Tunicates

Vase tunicate (Ciona intestinalis) and Clubbed tunicate (Styela clava)

What are They?

  • Invertebrate, filter-feeding animals that look like fingers or cylinders, with two siphons on the top.
  • They have a muscular skin that looks like a tunic and can retract or close their siphons when touched or disturbed.
  • When they do this, water may squirt out which is why they are nicknamed “sea squirts”.
Vase Tunicate
Vase tunicate.

Where did They Come From?

  • The vase tunicate is native to Northern European waters.
  • The clubbed tunicate originates from the western Pacific Ocean.

Where are They now?

Vase Tunicate
Vase tunicate.
  • Solitary tunicates are found in various locations in many waters throughout the world.
  • The vase tunicate has been observed in southern New Brunswick and Nova Scotia for over 100 years.
  • In 1997, a population explosion of the vase tunicate occurred in many sites on the south shore of Nova Scotia and in 2004, it invaded Prince Edward Island.
  • The clubbed tunicate arrived in Prince Edward Island in 1997 and is causing great problems for mussel farmers.

How/Where do They Live?

Clubbed Tunicate
Clubbed tunicate

Solitary tunicates are very hardy and can tolerate a wide range of water temperatures and salinities (salt content). They seem to prefer more sheltered bays where they like to grow attached to rocks, wharves, docks, fishing, and aquaculture gear as well as to shellfish such as mussels, scallops, and clams.

Clubbed Tunicate
Clubbed tunicate.

Vase and clubbed tunicates are very fast growing and can reproduce and release more than 10,000 eggs as early as eight to ten weeks old! Larvae swim in the water for a few days and then settle to grow. They live for one or two years.

Their tunic protects their internal organs. They pump water in through one siphon, filter the plankton and other small food particles through their digestive system, and then release the filtered water out through the other siphon.

Adult tunicates have few predators because of their thick and noxious skin. Crabs, sea stars or snails may eat juvenile tunicates. It is thought that these tunicates “hitchhike” on the hulls of boats or floating debris as juveniles or adults to invade other areas.

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

These solitary tunicates are fast-growing, very rapid breeders and highly efficient feeders. They are a great threat to biodiversity because they compete for food and can overgrow in areas, replacing native species. They are also a major pest for shellfish aquaculture because they like to grow on shellfish and underwater ropes, buoys, and cages. While shellfish farm¬ers have developed a number of methods to remove the tunicates, it takes considerable time and money.

Did you Know?

Vase and clubbed tunicates grow as individual or “solitary” species but can rapidly reproduce and grow to form thick clumps. They are a major threat to biodiversity because they compete for food and space with other filter feeders in the marine environment.

What can you do to Help?

There are no effective ways to get rid of tunicates once they are established in an area. Preventing their spread into new areas is the best option. Make sure that boat hulls and equipment are clean when moving from one area to another and follow the general guidelines recommended by Fisheries and Oceans Canada on the weblink below.

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