Invasive species continue to grow in waters around Charlotte County

(Wikimedia Commons/Public domain image) Botryllus schlosseri or star tunicate.

ST. STEPHEN – Tunicates are becoming a growing problem in the Bay of Fundy and scientists are working to learn more about these marine invertebrates.

Invasive tunicates have been coming into the waters around Charlotte County for decades. They were less a problem until recent years because the invasive ones were warmer water varieties and would die off in the winter when the temperatures in the Bay of Fundy dropped.

Over the past couple decades, temperatures in the Bay of Fundy have been rising, allowing the invasive tunicates to survive over winter and continue growing. A former employee of Fisheries and Oceans Canada (DFO) gathered data from 1989 to 2018 that shows temperatures rising approximately 2 C on average over the period.

“The problem is once they are in the ecosystem, there’s not a massive amount that you can do to get rid of them,” said Claire Goodwin, a researcher at the Huntsman Marine Science Centre in Saint Andrews.

She said researchers are working to determine which varieties are in the waters, where they are and how much they’re spreading.

Claudio DiBacco, research scientist at the Bedford Institute of Oceanography in Nova Scotia, is careful to note that not all tunicates are invasive. He distinguishes between non-indigenous and invasive species by how they interact with the new surroundings. Non-indigenous species don’t necessarily damage the ecosystem of the Bay of Fundy. Invasive species are the ones that do damage and begin to take over the environment.

“We have lots of non-invasive species, but very few we would outright call invasive,” he said.

From 2006 to 2022, DiBacco said researchers have discovered a growth from three varieties in 2006 to nine species in 2022.

Some of the species have amusing common names like pancake batter, or sea vomit (Didemnum vexillum or D. vex), sea squirt (Ascidiella aspersa), vase tunicate (Ciona intestinalis) and star tunicate (Botryllus schlosseri). Despite the fun names, some of these species can do extensive damage to ocean ecosystems.

DiBacco explained that, in the case of mussels, estimates are that by competing for food, tunicates are reducing “the growth rate of the mussels by 30 per cent,” meaning the mussels take longer to grow and reducing harvest volumes.

Scallop fishers in the Bay of Fundy are starting to see tunicates developing in the scallop beds. Lillian Mitchell, executive director of the Fundy North Fisherman’s Association, said fishers are finding scallops grown over with tunicates are more often dead. What they don’t know is what variety of tunicate they’re dealing with, whether the tunicates are causing the scallops to die, or if the tunicates are just growing over scallops that are already dead.

Association members took some photos during the 2022 season they sent to DFO.

“Basically the response we got back was it wasn’t possible to make an identification based on the photographs,” said Mitchell.

She said they have received feedback from DFO that “this invasive tunicate (D. vex) could potentially create an anoxic condition for the scallops,” but they won’t know without more testing and research. Anoxic waters are areas with a lack of oxygen in the water. The tunicates growing on the shells could make it impossible for the scallops to open, feed and filter.

Goodwin said they have tunicates growing over anemones on the seabed, “so they do have the potential, this sea vomit, to smother other marine life.”

Mitchell said the fisherman’s association is working with Goodwin at The Huntsman to source funding to sample the tunicates fishers are finding to determine if it is D. vex or something else. The Huntsman would test the samples to determine if it is D. vex or “just a benign tunicate that looks similar to D. vex.”

Mitchell is hopeful they will know about the funding by autumn so they can be ready for the scallop harvesting season that begins in January.

The association has not found tunicates to be an issue with the lobster fishery directly. The equipment lobster fishers use, ropes and traps, could act as a transmission mechanism to carry tunicates from one area of water to another.

DiBacco said many of these invasive species have come into the waters here either as larvae on the hulls of boats or in ballast water.

“The larvae also can move around in the sea water themselves,” said DiBacco. “I think they are thought to move with ship movements and also as people are moving things between different (ocean) agriculture sites, they could possibly transport invasive species that way as well.”

Goodwin said a national campaign has been started to educate people about the movement of invasive species on boats and other equipment and a program called clean, drain and dry has started to “make sure you’re cleaning things between different sites.” She said it applies to recreational boats as well as commercial gear.

DiBacco said the warming waters are contributing to growth of the creatures and even if there is a cold year, areas he calls “thermal refuges” can help the tunicates survive. Thermal refuges are pockets of water that stay warm. He said that happened in 2019. As the tunicates continue to grow in the waters around the Bay of Fundy, they also become more adapted to the waters and are better able to withstand a colder winter.

“The fact that it’s here and it has survived cold conditions at this range means that now it has time to adapt to the local environment,” he said, adding these species are very good at adapting quickly.

He said there are two factors playing into the species adaptability. One is shorter term temperature variations where they’re seeing larger seasonal fluctuations with warmer summers allowing for the tunicates to expand their range. He said they’re seeing seasonal fluctuations of two to four degrees compared to historical measurements. The other is the longer term, climate-related change in water temperatures that could allow the tunicates to stay in the waters and further expand their range.

Anaïs Lacoursiere, a researcher with DFO, is working to understand the ecology and makeup of tunicates. Her work is “making sure we understand their ecology, where they live and how is that affected by global warming.”

She’s also working on mapping distribution and spread by looking at the creatures at a molecular level. She is working with Goodwin, diving in the Bay of Fundy and said it’s “shocking how much they became really dominant in the natural substrate.”

She said she sees tunicates competing with other species for food and space. The adaptability is impressive to her as a researcher “if you have changes in the ocean like global warming and other stressors that affects local species in a negative way, whereas the invaders can adapt,” and be able to reproduce more than indigenous species.

“Biologically they are very impressive.”

DFO is working with international partners to do things like changing shipping lanes, rerouting ships through colder waters, to try to kill off larvae that may be on the hulls.

“These are barriers in the ocean that prevent the natural spread of these species and the idea is that if you understand where these natural barriers are, then you can use those for managing ship traffic,” said DiBacco.

Ballast water, he said, “is what introduced zebra mussels to the Great Lakes,” so researchers are trying to gain a better understanding of the impact of ballast water as a source of transmission for invasive species.

Hull fouling, or invasive species hitchhiking a ride on the exterior hull of a ship, is probably a bigger risk today than ballast water, DiBacco said. It’s an area researchers are working to better understand and if a vessel is going across one of the natural barriers, “maybe you require the ship to have its hull cleaned.”

DFO is also working with the Department of National Defense (DND) to help DND understand the risks of moving ships around the world and how the department can reduce the risk of transmitting invasive species to Canadian waters or from Canadian waters to elsewhere.

The adaptability of tunicates is the biggest concern of researchers, said Lacoursiere.

“I think that’s our biggest worry. The biggest worry is biodiversity. If you decrease biodiversity that means a loss of species interaction and a crash of many local species.”