Golden Star Tunicate
Botryllus schlosseri

Report a discovery in an unlisted area

If you think you’ve seen or caught a Golden Star Tunicate:

  • Do not release it into the water.
  • Catch it and keep it frozen. If you can’t do that, destroy it.
  • Note the location (with GPS coordinates if possible) as well as the observation date.
  • Contact Fisheries and Oceans Canada.

Golden Star Tunicate is an invasive colonial tunicate widely distributed throughout the world. It has been reported in eastern Canada and in the Gulf of St. Lawrence for several decades.

Identifying features

Golden Star Tunicate colonies often grow up to 10 cm in diameter. They can be distinguished from other types of tunicates by the star-shaped arrangement of individuals within a clear, firm, coat or tunic. Despite their name, they can be many different colours and patterns and colonies are usually two-toned (common colours include black, brown, bright orange and green). Colonies are typically densely packed into a mat that covers the underlying surface. Where space is limited, they may grow in lobes, with single layers of individuals folding over one another. Golden Star Tunicate colonies are arranged into a star or flower-shaped pattern; zooids are recumbent (positioned horizontal relative to the substrate) with the pointed end directed into the centre of the colony.

Similar species (native)

Can be mistaken for sponges, but sponges have a soft porous texture rather than a gelatinous one.

Where it has been found

The Golden Star Tunicate has been observed on the east and west coast of Canada. In Nova Scotia, Golden Star Tunicate has been observed for several decades at low levels along the Bay of Fundy coast, the Atlantic coast and in the Bras D’Or Lakes (Cape Breton). In the southern Gulf of St. Lawrence, this species has established in several bays along the coast of Prince Edward Island, northeastern and southeastern New Brunswick and Gulf shore of Nova Scotia.

In Newfoundland and Labrador, Golden Star Tunicate was first reported in Bonne Bay, on the west coast of Newfoundland and Labrador, around 1975. Approximately 30 years later, this species was confirmed at a number of sites along the south coast of insular Newfoundland. On the Canadian West coast this tunicate has been reported from the Strait of Georgia and West Coast of Vancouver Island.

Golden Star Tunicate distribution in Gulf region

Golden Star Tunicate distribution in Gulf region
Click image to enlarge

Ecological and economic impacts

Golden Star 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.

Golden Star Tunicate is mostly composed of water. It grows rapidly and may cover surrounding plants and animals, depriving them of sunlight or food. Golden Star Tunicate may even suffocate smaller organisms such as juvenile mollusks, and may cause organisms that attach to marine surfaces to be more vulnerable to being moved by water currents. All of this makes the Golden Star Tunicate disruptive to shellfish harvesters, aquaculture farmers, and aquatic organisms that live on the bottom of the ocean.

Origins and mode of arrival

Native to the Mediterranean Sea, but is now considered cosmopolitan as it can be found on all continents except Antarctica.

Mode of dissemination

The Golden Star Tunicate reproduces two ways: when fragments of a colony break off and bud elsewhere, and by the production of eggs that hatch into free-swimming larvae. Both fragments and larvae settle and grow on a range of artificial surfaces such as buoys, boat hulls, rope, wharf pilings, and floating docks as well as on natural surfaces such as rocks, mussels and kelp. Larvae released into the water column settle within 24 to 48 hours, and only travel over small distances. Colony fragments may reproduce for up to 40 days and may disperse over much greater distances. Colonies grow once water temperatures exceed 6º C. Egg production, larval development, and growth start at water temperatures greater than 12º C. During the winter, when water temperatures drop below 6º C, colonies may enter a resting phase, reduce in size or die. Transport of free-swimming larvae in the ballast water of ships is unlikely because of their short larval cycle, but ballast may contain floating debris that could serve as a vector for adult forms.

Government action

Scientific research

As the ocean grows warmer, it is important to continue to monitor any changes in the Golden Star Tunicate’s distribution and range expansion. This will help in preventing and managing its spread.

Golden Star Tunicate in Newfoundland and Labrador Waters

Controlling abundance

Click images to enlarge.

Distribution Location and Bay
  • Argentia: Placentia Bay
  • Arnolds Cove: Placentia Bay
  • Baine Harbour: Placentia Bay
  • Bonne Bay: Bonne Bay
  • Codroy: Southwest Coast
  • Fox Harbour: Placentia Bay
  • Foxtra: Conception Bay
  • Garden Cove: Placentia Bay
  • Harbour Breton: Fortune Bay
  • Hermitage: Hermitage Bay
  • Kingwell: Placentia Bay
  • Lamaline: Placentia Bay
  • Little Bay: Placentia Bay
  • Little St Lawrence: Placentia Bay
  • Long Harbour: Placentia Bay
  • Long Pond: Conception Bay
  • NE Arm Placentia: Placentia Bay
  • North Harbour: Placentia Bay
  • North Tilt Island: Placentia Bay
  • SE Arm Placentia: Placentia Bay
  • Spencers Cove: Placentia Bay
  • St Pauls Inlet: Northern Peninsula West
  • Swift Current: Placentia Bay

Tunicates can spread through the movement of fishing gear, shellfish, and recreational and commercial vessels. To control the spread of Golden Star 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 cleaned out and the boat should be allowed to dry for 24 hours. Also, because Golden Star Tunicate can rapidly colonize and establish large, self-sustaining populations, it should be removed from wharves and surrounding structures.

When combined with surveys (see map of where the Golden Star Tunicate are located), using genetic tools to find eggs and larvae of Golden Star Tunicate will help target control and prevention efforts. Improving our understanding of its lifecycle will help us to establish where and when to apply these efforts. Especially important is the removal of Golden Star Tunicate before it reproduces each year. Recent work by Memorial University of Newfoundland and Fisheries and Oceans Canada at Arnold's Cove indicates the reproduction cycle starts in late July and continues through early October.

For further information

References

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