At a dock on Cape Cod鈥檚 Buzzards Bay, a group of researchers and marine biology students lie on their stomachs, peering over the wooden planks to examine what living things are stuck underneath.
Earth Day
This story is part of a New England News Collaborative series marking Earth Day 2025.[/keyfigures]
Using fishing nets and kitchen spatulas, they scrape samples into plastic trays for a closer look. Kristin Osborne, a sea squirt expert and assistant professor at the Massachusetts Maritime Academy, likes to use her bare hands.
鈥淚 said I wasn鈥檛 gonna get down here and do this, but I can鈥檛 help myself,鈥� Osborne said with a laugh while reaching into the chilly ocean. She has a sea squirt tattoo on her left middle finger.
Sea squirts are a type of filter feeding marine invertebrate officially known as tunicates. These colorful blobs can squirt water when removed from their aquatic homes, earning them the nickname.
Some tunicates are native to New England, but most of what this research group finds are invasive species. Scientists believe a lack of predators and warmer ocean waters caused by climate change are helping non-native sea squirts thrive up and down the New England Coast.
Sea squirts spend most of their lives stuck to hard surfaces like docks, the ocean floor, fishing gear or even other animals. This can be a problem for commercial fishing since the creatures can clog up equipment and may push out native species.
At the dock, sophomore Dan Kowalski holds up a mussel covered in what looks like pancake batter. It鈥檚 an invasive sea squirt, growing over the opening at the top of the mussel鈥檚 shell.
鈥淚t makes it harder for the mussel to filter feed because it makes it harder for them to open,鈥� Kowalski explained. He said students regularly pull up baskets full of dead oysters and mussels covered in sea squirts.
This wasn鈥檛 an issue two decades ago, according to scientists. Marine biologists believe invasive sea squirts likely arrived in these waters after hitching rides on boats from around the world.
Tunicates spread quickly because they don鈥檛 have any natural predators here, Osborne said. And they鈥檙e good at tolerating a variety of environmental conditions, which gives them an edge over their native counterparts that aren鈥檛 used to much environmental change.
Plus, some species of sea squirts grow in large colonies, forming thick mats that are difficult to get rid of.
鈥淚f you were to, let鈥檚 say, power wash it off of some gear or the side of a boat, you鈥檙e fragmenting it. So it鈥檚 just being spread,鈥� Osborne said. 鈥淎ll these little tiny pieces become new colonies of themselves.鈥�
She鈥檚 noticed more of these invasive creatures in Buzzards Bay in recent years. 鈥淚t is more typical when you pull up any sort of sample from the dock here to get a non-native species than a native one,鈥� Osborne said.
Climate change鈥檚 role
Scientists suspect are giving invasive species like sea squirts more time to reproduce, which fuels their population growth.
鈥淲e鈥檙e starting to have these warmer winters. Then species can gain a foothold,鈥� said Aly Putnam, a marine ecologist at the University of Massachusetts Amherst.
It also means the range of places where a non-native species can comfortably live is expanding. Some species are now able to survive in locations where they previously couldn鈥檛, Putnam said.
For example, certain have been increasingly observed in northern areas, like the Gulf of Maine.
Because non-native sea squirts can tolerate environmental changes in ways native species might not, the new arrivals can disrupt food webs. In extreme cases, they can lead to species extinctions, said Lexie Neffinger, a coastal habitat and water quality specialist for the Massachusetts Office of Coastal Zone Management.
鈥淭here鈥檚 a certain equilibrium when you have native species that have evolved together over time,鈥� she said. 鈥淚t鈥檚 really a question of biodiversity.鈥�
Completely eradicating an invasive marine species once it鈥檚 made a home presents particular challenges. Unlike on land, where it might be possible to target a single plant species with an herbicide, for example, Neffinger said treating a whole body of water would affect native species, too.
鈥淕etting underwater and being able to remove every single individual of that species that are all reproducing is nearly impossible,鈥� she said.
Instead, Neffinger said the goal is preventing further spread. And that requires data on where invasive species are moving.
鈥楾he finger on the pulse鈥�
Every five years, Neffinger鈥檚 office coordinates a large survey of invasive marine species stretching from southern Massachusetts all the way to Casco Bay in Maine.
A team of researchers scrape and pluck living things off docks and marinas, pulling up everything from crabs and sea squirts to algae. They鈥檝e been counting established invasive species and logging new ones .
The most recent survey, conducted in 2023, found an increase in the overall number of invasive species. The team identified 32 in total, and a quarter of them were sea squirts. They also found a type of small filter feeding animal that lives in colonies, called bryozoans, which hadn鈥檛 been identified in any previous surveys.
Adrienne Pappal, who oversees this effort, said the majority of what the team sees are still native species. But the surface area of non-native species is increasing.
And along with more observations of established invasive species, Pappal said, 鈥渢ypically we are finding some new species each time.鈥�
Monitoring where these species are moving allows state officials to do outreach and education on how to manage them. It also provides important baseline data for a changing climate, Pappal said. The surveyors collect information on water temperatures, salinity levels and even boat traffic.
鈥淭he more we can get long-term data and long-term monitoring, the better we鈥檙e going to understand our world and be able to prepare for future changes,鈥� she said.
Putnam, the UMass Amherst marine ecologist, calls this large survey the 鈥渇inger on the pulse鈥� of invasive marine species in New England. She participates in the survey, as well as other monitoring efforts in the region.
鈥淜nowledge is power,鈥� she said. 鈥淓ven if a [new invasive] species isn鈥檛 in high density yet, it鈥檚 important to know who is here.鈥�
Searching for the 鈥榯eeny, tiny鈥�
These efforts also engage students like Aidan Webb, who helps out with an annual that recruits volunteers around Massachusetts.
鈥淚 like being out in the field and at the locations where you pull up just a giant chunk of sea squirts and all the other seaweeds and stuff that鈥檚 mixed in,鈥� he said. 鈥淎nd then just sorting through it and seeing what you can find.鈥�
Webb said he鈥檚 gotten good at identifying what鈥檚 native and what鈥檚 not.
On the Buzzards Bay dock, he rattles off names as he pokes through a tray of specimens: 鈥淲e got the skeleton shrimp here. A mud crab.鈥� He also finds a common non-native sea squirt called .
When Webb spots a grape-sized tunicate called molgula, Osborne, the sea squirt expert, gets excited. The single 鈥渢eeny, tiny molgula鈥� is a native species, she said.
It鈥檚 one of the only native sea squirts her students find all day.
Once the group finishes scraping, they tip the contents of the plastic trays back into the ocean 鈥� invasive species and all. The creatures are so well established in these waters, Osborne says, removing them wouldn鈥檛 make a dent.
鈥淭he best approach,鈥� she added, 鈥渨ould be to keep them out in the first place.鈥�
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