Sunday, January 29th, 2023
Sunday, January 29th, 2023

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Mon shrimp finding puzzles scientists

By Deborah Weisberg Contributing Writer

Pittsburgh — A creature you’d expect to find in the Louisiana
Delta appears to have taken up residence in the Monongahela River
near Pittsburgh.

Shrimp – not the jumbo kind seen on restaurant menus, but its
smaller cousin the grass shrimp – were captured by scientists
bottom trawling a 40-mile stretch of the Mon from Fayette City to
the West Virginia border this summer.

”We’re really scratching our heads about it,” said David Argent,
a California University of Pennsylvania biology professor who
captured the tiny, translucent crustaceans at Port Marion near West
Virginia and at the mouth of Little Redstone Creek in Fayette City.
“But wow, it’s really neat … the last thing we expected to
find.”

The discovery is significant because the species, known as
Palaemonetes kadiakensis, are native to the Mississippi Drainage –
of which the Monongahela is a part – and an indication of good
water quality, Argent said. More than half of the 11 shrimp he
caught carried eggs. Benthic trawling has never been performed
before on the Mon, so how long the shrimp have been there is
anyone’s guess, but Argent said capturing such a small number
suggests they are relative newcomers, and only beginning to expand
their range in the Mon’s improving water.

He said he’s ruled out that the shrimp were planted, like the
tilapia that surfaced in Braddock this month. “I showed them to my
colleague Bill Kimmel, and we think they’re the real deal,” Argent
said. “They’ve probably never been seen this far north before,
although they’ve been in the drainage for a hundred million
years.”

Something similar occurred in Lake Erie, according to Ed
Masteller, a biologist specializing in benthic communities and a
professor emeritus at Penn State University’s Behrend College. “I
found a few grass shrimp in Erie when I came here in 1967, then I
didn’t see them for years until they started showing up again in
large numbers, kind of like mayflies, when the habitat improved
enough for them to reproduce,” he said. He even considered trying
to raise grass shrimp in Erie, as an academic experiment, several
years ago. “It was exciting to me, because they seem to be
indicators.”

Argent found the Mon River shrimp in eelgrass, a plant with
1-inch blades seen undulating in the water, and native to the Mon
but seldom found in the Allegheny and Ohio. “We also got a lot of
little bluegills, rock bass, smallmouths and spotted bass in the
same eelgrass, so it appears it’s a kind of nursery area,” he said.
Six of the shrimp had eggs tucked up underneath their legs, which
on their 2-inch long, nearly transparent bodies appear as tiny
green dots.

Argent said he’s trying to figure out how the shrimp got to
Pennsylvania. They could have “hitchhiked” in the ballast water of
a boat that had been to the Gulf of Mexico or some other coastal
area where shrimp are more at home, or they might have alternately
swum and drifted up on their own. The Mon flows north through West
Virginia. Shrimp power themselves with their tails and have big
eyes and long antennae that help them forage, mostly for plankton
and other microscopic matter. Their translucence helps them elude
predators.

Although grass shrimp are more common to brackish or estuarial
water, Argent said ”the temperatures and habitat on the Mon are
suitable enough for them. They like a silty habitat, which the Mon
certainly has. You can stand on Mount Washington and see sediment
plumes where the Mon mixes with the Ohio.”

As bottom-dwelling filter feeders, grass shrimp would survive
over the long term only by being able to withstand the heavy metals
and other toxins embedded from the region’s industrial past. “The
only way to really know how much pollution they’re absorbing is to
mash them up and study their tissue, and I have no interest in
doing that,” said Argent, who has the shrimp pickled in a jar in
his lab. “They wouldn’t be attempting to breed if conditions in the
river were that poor, chemically or otherwise.”

Equally encouraging are the other species Argent’s trawling
operation yielded, including a big bounty of Johnny darters and a
significant number of channel darters and silver chubs, which are
state-threatened species.

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