Also called: Sea Squirts
Do you think you have discovered an aquatic invasive species?
- Do not return the species to the water.
- Note the exact location (GPS coordinates) and the observation date.
- Take photos.
- Take note of identifying features.
- Report an Aquatic Invasive Species, depending on where you are.
- What you can do to reduce the risk.
Tunicates are aquatic animals with a sac-like body protected by a coat or ‘tunic’. They live in large colonies and feed by filtering sea water through their bodies. Researchers think that tunicates first appeared over 500 million years ago.
Tunicates are small marine animals that spend most of their lives attached to an underwater substrate. They are named "tunicate" for their thick skin resembling a tunic. They feed by filtering seawater through their siphons.
Several invasive species of tunicates threaten our waters. They are found on the Atlantic and Pacific coasts and can be spread by ocean currents as well as by human activities.
Tunicates are typically found in sheltered areas, attached to rocks, eelgrass, seaweeds, other animals or on man-made structures such as boat hulls, buoys, ropes, anchors, floating docks, aquaculture gear and wharf pilings.
Solitary or colonial
Tunicates can be either solitary or colonial. Several colonial species form gelatinous mats that may cover almost anything underwater. The colonies are made up of many individual organisms, called zooids, embedded in a common matrix. For certain species, colonies can form folds and lobes that hang down in the water.
Solitary Invasive Tunicates
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”.
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.
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.
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.
Colonial Invasive Tunicates
- 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.
How did they get their names?
The Pancake Batter Tunicate 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).
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.
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.
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.
For more information
- Aquatic Invasive Species - Identification Booklet [PDF]
- Science advice from a risk assessment of five sessile tunicate species [PDF]
- Marine screening-level risk assessment tool for aquatic non-indigenous species [PDF]
- Risk Assessment for Two Solitary and Three Colonial Tunicates in Both Atlantic and Pacific Canadian Waters [PDF]
- QBRAT Case Study [PDF]
- Workshop Proceedings [PDF]
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