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- identifying features
The Violet Tunicate is a colonial tunicate, usually made of single colour colony (purple, pink, yellow, white, or orange). Adult violet tunicates grow in colonies of approximately 10 cm in diameter. The colonies are often densely packed together and can grow mats or ‘lobes’ over surrounding terrain that are up to 5 cm long, zooids are upright (positioned vertical relative to the substrate) and arranged into systems of elongated, meandering rows. Violet tunicate can be distinguished from other tunicate colonies by the apparently random arrangement of individuals. They have distinct ridge or track-like patterns on the surface of their fleshy coat. Violet tunicate has fewer colour patterns than the golden star tunicate and is typically evenly coloured in shades of orange, burgundy, dull pink, lavender or purple.
Similar species (native)
Violet tunicate can be mistaken for sponges, but sponges have a soft porous texture rather than a gelatinous one.
Where it has been found
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. In the southern Gulf of St. Lawrence, it is widely distributed along the Prince Edward Island coast and is appearing on Gulf Shores of Nova Scotia and southeastern New-Brunswick. In Newfoundland and Labrador, it was first identified in Belleoram, in 2007. As of 2010, it has not spread beyond the waters of Belleoram.
In British Columbia this colonial species is widely distributed with reports from the Strait of Georgia, West Coast of Vancouver Island, the North Coast, and most recently Haida Gwaii.
Ecological and economic impacts
Violet tunicate is a filter feeder, getting nutrients from phytoplankton (algae), bacteria and other small organic things that float in the sea. In large numbers, the tunicate competes for food with other filter feeders, such as mussels and scallops.
Violet tunicate is mostly composed of water. It grows rapidly compared to other marine organisms. It may cover surrounding plants and animals and deprive them of sunlight or food. Violet tunicate may even suffocate smaller organisms, such as juvenile mollusks. It releases a chemical that can make it hard for other organisms to attach properly to surfaces. These organisms then become vulnerable to being removed by water currents. This chemical can also repel and inhibit growth in predators. All of this makes the violet tunicate harmful to shellfish harvesters, aquaculture farmers, and aquatic organisms that live on the bottom of the ocean.
Origins and mode of arrival
Violet tunicate is an invasive colonial tunicate native to the northwestern Pacific Ocean (Asia).
Mode of dissemination
The lifecycle of violet tunicate is not fully understood but we know that they can reproduce in two ways: when fragments of a colony break off and bud elsewhere, and by the production of eggs which hatch into free-swimming larvae. Colony fragments may travel over great distances and the fragments are able to reproduce for up to 40 days. Larvae released into the water column settle within 48 hours, and only travel small distances.
Fisheries and Oceans Canada is studying the Violet Tunicate population to improve its understanding of how it reacts and adapts to Canadian conditions.
Tunicates can spread through the movement of fishing gear, shellfish, and recreational and commercial vessels. To control the spread of violet tunicate, boat hulls and fishing gear should be visually inspected and cleaned when necessary. To prevent the spread of living fragments, water inside boats should be drained and the boat should be allowed to dry for 24 hours. Also, because violet tunicate can rapidly colonize and establish large, self-sustaining populations, it should be removed from wharves and surrounding structures.
Violet tunicate in Newfoundland
Discovery and Survey Findings
During a survey in September 2007, violet tunicate was discovered in Belleoram, Fortune Bay (NL). This is a concern to the aquaculture industry in Newfoundland. However, this species has not yet been found in local mussel farms. Fortunately its distribution appears to be restricted to Belleoram where it is being found on wharf structures, ship hulls, plastic surfaces, rocks, and wild mussels.
This species still poses a potential risk to bottom dwelling aquatic animals in other parts of Newfoundland and Labrador so it is important to continue to monitor other areas. This will help in the long-term management and prevention of the spread of violet tunicate.
In 2008-2009, Fisheries and Oceans Canada worked with Memorial University of Newfoundland to test various mitigation methods in Belleoram. This included wrapping wharf pilings and covering affected rocks and structures with plastic. While this killed many violet tunicate, they eventually came back and resettled in large numbers on and around the treated surfaces. As of 2010, other methods of prevention and control are being tested, including the introduction by Fisheries and Oceans Canada of sea urchins to the Belleoram wharf. Sea urchin eat violate tunicate and the department is studying whether the sea urchins will control the population through predation.
Continuing survey and monitoring work will improve our understanding of the violet tunicate. Understanding an organism's lifecycle in its newly invaded environment helps us to establish where and when to target prevention and control efforts. It is especially important that we understand how violet tunicate over-winter and when they sexually reproduce. When combined with surveys, using genetic tools to find eggs and larvae of violet tunicate will help us target our efforts.
For further information
- Canadian Science Advisory Secretariat (CSAS) Publications
- Invasive Tunicate - Fact Sheet
- Aquatic Invasive Species Identification Booklet (PDF)
Fisheries and Oceans Canada – March 2013
- Biological Synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus (PDF)
Fisheries and Oceans Canada – 2006
- Aquatic Invasive Species: Violet Tunicate in Newfoundland and Labrador Waters
Fisheries and Oceans Canada - 2011
- Science advice from a risk assessment of five sessile tunicate species (CSAS SAR - 2012/049)
- Berrill, N.J. 1950. The Tunicata, with an account of the British species. Ray Society, London. Publication 133: iii + 354 p.
- Callahan, A.G., Deibel, D., McKenzie, C.H., Hall, J.R., et Rise, M.L. 2010. Survey of harbours in Newfoundland for indigenous and non-indigenous ascidians and an analysis of their cytochrome c oxidase I gene sequences. Aquat Inv 5: DOI 10.339/ai2010.5.1.
- Carver, C.E., A.L. Mallet et B. Vercaemer. 2006. Biological synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus. Can Mans Rep Fish Aquatic Sci, 2747, MPO. 42 p.
- Lambert, C.C. et G. Lambert. 2003. Persistence and differential distribution of nonindigenous ascidians in harbors of the Southern California Bight. Mar Ecol Prog Ser, 259:145-161. Oka, A. 1927. Zur kenntnis der japanischen Botryllidae (vorlaufige Mitteilung). Proc Imp Acad, 3: 607-609.
- Van Name, W.G. 1945. The North and South American ascidians. Bull Am Nat Hist, 84 p.
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