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Courtesy photo.




Invasion of the sea squirts
Marine species infestation spreading in warmer waters

02/22/18
By Ryan Lessard news@hippopress.com



 A species of tunicates, also known as sea squirts, from the Asian side of the Pacific Ocean, has been introduced to the Gulf of Maine and is reproducing quickly, which will likely have negative effects for local industry and the ocean ecology.

 
What are they?
The Atlantic Ocean is no stranger to tunicates, which are gooey filter-feeding blobs that latch onto hard surfaces and spread.
Jenn Dijkstra, a research assistant professor at the School of Marine and Ocean Engineering at the University of New Hampshire Center for Coastal and Ocean Mapping, recently published a study that predicts a rapid expansion of an invasive species of tunicate from the Pacific Ocean.
“These guys are colonial animals that are in a gelatinous material. So there’s many individuals that are in this sort of gelatinous material,” Dijkstra said.
The invasive sea squirts, known by the scientific name Botrylloides violaceus, look like orange, bumpy masses of brain-like tissue that can be found on rocks, docks and ship hulls. They reproduce sexually and asexually (when individuals duplicate themselves). The former process sends young into the water column to settle a new colony in a different area, while the latter allows existing colonies to spread across more surface area and increase in size.
 
Invasion
The Pacific tunicates Dijkstra studied for her research likely came to the northern Atlantic Ocean by hitching a ride on the hulls or in the ballast water of ships that traveled from the other side of the planet.
Now that they’re here, like many other invasive species, they don’t have much standing in their way.
“They’ve lost a lot of the biological control mechanisms that they would have in their native ecosystems,” Dijkstra said.
And they now have an added benefit from increasing ocean water temperatures in the Gulf of Maine, Dijkstra said, which recent studies have shown is warming more rapidly than the rest of the planet’s ocean waters, and that warming is being caused by climate change.
The warmer temperatures gives the sea squirts a longer reproduction season.
Dijkstra has already found sea squirts have expanded rapidly in ocean waters off the coast of New Hampshire. She predicts their reproduction will be able to double over the next few years.
That’s based on projections by the Intergovernmental Panel on Climate Change, which expects a 2-degree Celsius increase (3.6 degrees Fahrenheit) in the coming years.
Short of addressing those increasing temperatures, there’s not much that can be done to curb the spread, Dijkstra said.
“Once they’re established in an area, it can be pretty challenging to try to control their populations,” Dijkstra said.
There are some snails and starfish that feed on them, but they don’t make much of a dent compared to how fast the sea squirts reproduce. 
The spread can have a serious effect on the ecology.
“They tend to crowd out native species,” Dijkstra said.
Tunicates eat plankton, like other filter feeders. As they grow in number, they can start to take food away from other species. The problem is particularly noticeable with mussels and oysters, which get covered by the orange goo.
Harvesters increasingly have to deal with the added weight when pulling them up, and the additional efforts to powerblast the shellfish to clean them off.
Some of those mussels and oysters have noticeably less flesh because they aren’t able to get as much food.





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