09/24/2026
I stopped to chat with Department of Fisheries and Oceans who were doing research down at the Shelburne Yacht Club.
Ongoing science research matters and our marine health matters. of Fisheries and Oceans. DFO AIS ([email protected]
Department of Fisheries & Oceans Canada
To all the citizen scientists out there. Here is a bit more on this invasive species:
This pictured cluster found by DFO at the Shelburne Yacht Club is a colonial tunicate - an invasive sea sq**rt. From the translucent, grape-like blobs with orange inside, it looks like Violet Tunicate - Botrylloides violaceus - one of the 4 invasive tunicates that have established on the south shore of Nova Scotia since 2012.
It is the same group DFO tracks along with European Sea Sq**rt Ascidiella aspersa, Clubbed Tunicate Styela clava, and Golden Star Tunicate Botryllus schlosseri.
What you are seeing:
Colonial sea sq**rts are not one animal, but hundreds of tiny zooids sharing a jelly-like tunic. That jelly you are holding is mostly water.
Violet tunicate forms exactly those lumpy, gelatinous mats that overgrow ropes, docks, mussel lines and boat hulls. Color varies from orange-brown to violet, semi-translucent.
They are filter-feeders - each zooid pumps water through siphons and filters out plankton.
DFO is performing research in Shelburne:
Origin and spread: Native to the northwest Pacific, it came to the U.S. in the 1980s and was first detected in Canada on the south shore of Nova Scotia in 2012. Since then it has spread to the Bay of Fundy coast of New Brunswick. Larvae don't swim far - it hitchhikes as adults on hulls, floating debris, ropes and aquaculture gear.
Ecological and economic impact: It grows extremely fast - up to 20mm per month, matures in 8-10 weeks and produces >10,000 eggs per individual. It can dominate new surfaces at the expense of other fouling species. For mussel growers and yacht clubs, that means:
- Competes with mussels and other native filter-feeders for food
- Weighs down lines - what was a light rope becomes 3-5 times heavier
- Blocks cages and reduces oxygen for fish, creates huge drag on boats
What residents who connect with the ocean environment can do:
- Don't put these invasive species can do. Do not put this species back in the water. If it's on removable gear, bag it and dispose on land well above the tide line to die.
- Clean, Drain, Dry: Power-wash boats, ropes, fenders, and check hulls and sea chests. Let gear dry for 24h+ between bays if possible.
- Report it: DFO Maritimes wants reports for aquatic invasive species:
1. Take photos
2. Note exact location (Shelburne Yacht Club dock, GPS if you have it) and date
3. Contact DFO to report - email [email protected] or call 1-888-435-4040 - they have a specific "Report it" process for European Sea Sq**rt and Clubbed Tunicate that applies to all invasive tunicates
This is part of the annual biofouling monitoring DFO has run since 2006 for invasive tunicates on the Atlantic shore of Nova Scotia. Your sighting helps track the spread in Shelburne Harbour.
If you are pulling winter gear out soon, a good pressure wash on the hard and letting it dry before it goes back in next spring is the best local control.
Impact of Aquaculture equipment in the Shelburne Harbour
There is a known link, but it's not that the salmon cages created the sea sq**rt. It's that they give it a perfect home and a way to spread in Shelburne Harbour.
What DFO has documented:
Aquaculture gear is prime habitat.
Shelburne Harbour has had a marine cage site for Atlantic salmon and rainbow trout since 2000 - AQ #1192, now Kelly Cove Salmon Ltd. at 9.36 HA near Sandy Point / McNutt's Island.
Invasive tunicates love any artificial hard surface in sheltered harbours:
pier pilings, jetty walls, floating docks, buoys, vessel hulls, submerged ropes
Fish cages add a huge amount of that - nets, ropes, floats, anchor lines that sit in the water year-round.
Why fish farms can make it worse:
Two mechanisms:
Food: Fish cages release nutrients (feed and waste). That fuels phytoplankton blooms - which is exactly what filter-feeding tunicates eat. So they grow faster and thicker near farms.
Fouling impact: DFO notes "an overgrowth of vase tunicates on fish cages in aquaculture facilities can block off the cages, leading to decreased oxygen levels for the fish dwelling within". The colonies are mostly water, so a rope that was light becomes 3-5 times heavier very quickly. That creates drag, blocks water flow, and makes gear very hard to handle.
How they arrived in Shelburne
They didn't start here. The four problem species - including the violet tunicate Botrylloides violaceus that looks like your photo - were first introduced to New England in the 1980s and were first detected on the south shore of Nova Scotia in 2012. Since 2006 DFO has run a monitoring program placing collectors at public wharves, marinas and aquaculture leases along the coast of Nova Scotia to track them.
The main way they move between harbours is hitchhiking - as adults on boat hulls, or as larvae in water moved with shellfish gear, ropes, or cages. Shelburne Harbour is busy with fishing boats, pleasure craft at the Yacht Club, and aquaculture service vessels, so once established, it's easily moved around the harbour.
So the picture is: Aquaculture didn't create the invasive tunicate, but the combination of warm, sheltered harbour water, lots of permanent hard surfaces, nutrient-rich water, and movement of gear and boats between Sandy Point, the inner harbour, and the Yacht Club makes Shelburne Harbour ideal for it to take hold and spread.
If folks are seeing heavy growth this year, it would be worth letting both DFO AIS (AIS-EAE know. [email protected]
Take a photo and send it on to DFOโ
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