By TODD McLEISH/ecoRI News
contributor
During a class field trip to
Mackerel Cove in Jamestown, R.I., in 2017, University of Rhode Island student
Jacob Reilly picked up an unusual brown seaweed that looked like a hollow ball
and asked his professor what it was. The answer was a surprise.
Reilly had stumbled upon the first
appearance in Rhode Island of what has come to be called sea potatoes
(Colpomenia peregrina), an invasive seaweed native to the coast of Korea and
Japan that grows on top of other seaweeds.
“It’s not a parasite; it just settles and grows on top of other algae,” said Lindsay Green-Gavrielidis, a marine ecologist and URI postdoctoral researcher who teaches the class.
“We don’t know what impact it’s having on native seaweeds, though we hypothesize that it may be in direct competition for nutrients and light. But nobody has done any research to quantify its impact.”
Green-Gavrielidis has a history with
the invader. Sea potatoes had been unintentionally introduced to Europe
sometime in the early 1900s, probably in ship ballast, and from there it made
its way to Nova Scotia in the 1960s.
It took until 2010 for it to be discovered in the Gulf of Maine, when Green-Gavrielidis found it while conducting research for her doctorate at the University of New Hampshire.
It took until 2010 for it to be discovered in the Gulf of Maine, when Green-Gavrielidis found it while conducting research for her doctorate at the University of New Hampshire.
In addition to the ball-shaped form
it typically takes, the seaweed also forms a crust that grows on rocks that
easily goes unnoticed, so Green-Gavrielidis speculated that it may have been
“hiding out for a long time like that, and then when the conditions were right
the ball form started appearing.”
The appearance of sea potatoes along
the Rhode Island coast is significant because it has crossed what
Green-Gavrielidis calls a major biogeography boundary: Cape Cod.
The waters to the north of Cape Cod are dominated by the Labrador Current from Greenland, which makes for colder, more nutrient-rich waters. South of the Cape is dominated by the warm Gulf Stream.
The waters to the north of Cape Cod are dominated by the Labrador Current from Greenland, which makes for colder, more nutrient-rich waters. South of the Cape is dominated by the warm Gulf Stream.
“What it says about sea potatoes is
that it has a really broad tolerance for a variety of conditions, and not many
species can do that,” she said. “Most species don’t have the ability to move to
such very different places. Species that are successful invaders do. We were
hoping it wouldn’t be able to cross into this geographic region because of the
different conditions.”
To determine how common sea potatoes
are in Rhode Island waters, Green-Gavrielidis conducted a methodical search for
it at 13 sites along the state’s coastline last year and conducted several
quantitative surveys to compare its abundance to a similar native species
called sea cauliflower.
In addition to Mackerel Cove, sea
potatoes were also found at East Beach and Ninigret Pond in Charlestown and
South Ferry Beach in Narragansett.
It wasn’t found any further north in Narragansett Bay than South Ferry Beach, perhaps because the native seaweed it is most commonly associated with, rockweed, is not found in abundance in the upper bay. No sea potatoes were found in Westerly or eastern Connecticut, either, so it hasn’t likely found its way into Long Island Sound yet.
It wasn’t found any further north in Narragansett Bay than South Ferry Beach, perhaps because the native seaweed it is most commonly associated with, rockweed, is not found in abundance in the upper bay. No sea potatoes were found in Westerly or eastern Connecticut, either, so it hasn’t likely found its way into Long Island Sound yet.
“The biomass we found in Rhode
Island is much lower than what we found in the Gulf of Maine, so maybe it
hasn’t been here as long,” Green-Gavrielidis said. “That might also be because
the environmental conditions are such that it’s not doing so well here. We do
have some preliminary data that shows that there are herbivores — snails
primarily — that eat it, so that’s good.
“Often you think that when a new
species comes on the block, there isn’t something that consumes it. But we’ve
done studies that show that the common periwinkle will readily and happily pursue
it.”
That’s a good sign, since there is
little that can be done to stop it.
“We need to continue monitoring it
to see if its going to increase in abundance,” she said. “We expect it to
continue spreading. Whether it moves up into the bay or west to Long Island
Sound is unknown. And whether it’s a good thing, a bad thing, or neither, only
continued research can tell us.”
Green-Gavrielidis and URI colleague
Niels-Viggo Hobbs will be conducting a new research project this summer and
fall that involves sampling rockweed habitats — the native seaweed most closely
associated with the sea potato invasion — so they will be keeping an eye out
for the newly arrived seaweed. Their students are also conducting laboratory
studies to determine whether native seaweed-eating marine life will eat it and
if it is preferred over native seaweeds.