Add a bug-eyed shrimp to the ballooning list of Great
Lakes invaders that has likely hitchhiked its way into the region aboard an
overseas freighter, and nobody can say we didn't have fair warning it was
coming.
Eight years ago, two researchers at a Canadian
university predicted the half-inch, bright orange Hemimysis anomala was
a likely candidate to follow other notorious Caspian Sea region invaders such
as the zebra mussel into the Great Lakes, if more wasn't done to stop the
discharge of contaminated ballast water from oceangoing freighters traveling up
the St. Lawrence Seaway. On Nov. 7, the
shrimp turned up about 70 miles from downtown Milwaukee, near Muskegon, Mich.
"You could see them free-swimming," said
Steve Pothoven, a fishery biologist with the National Oceanic and Atmospheric
Administration, who spotted the shrimp with his colleagues. "I'd describe
it as a swarm."
Anthony Ricciardi of McGill University in Montreal,
one of the scientists who predicted the shrimp's arrival, describes it
differently. It is another sign, he said,
of an "ecological takeover" of the Great Lakes by species native to
the Black and Caspian Sea regions. Ricciardi has no problem ticking off
examples. "The dominant mollusk in
most parts of the Great Lakes is now the zebra and quagga mussel," he
said. "The dominant zooplankton is the fishhook water flea. . . . our
bottom-dwelling fish are becoming more and more dominated by the round goby and
ruffe. And now we have another one."
This new species of shrimp is likely to turn up in
other areas of the Great Lakes, speculated research scientist David Reid, who
works with Pothoven at NOAA's Great Lakes Environmental Research Laboratory.
The reason: The Muskegon port typically receives very little overseas traffic.
That, he said, means the initial invasion likely happened somewhere else in the
lakes.
The fat-rich shrimp, a high-quality food source, have
actually been planted in some reservoirs in Europe to boost fish populations.
The problem is the shrimp themselves feed on tiny zooplankton and phytoplankton that directly or indirectly
sustain the Great Lakes native fish species, said Reid. "It will have an ecosystem effect. How
significant that will be, we don't know," he said.
Ricciardi, recognized as one of the foremost
authorities on Great Lakes invasions, predicts the impacts will be big. "I don't expect this to be
benign," he said. "You're going to get the biggest disruption from
something that's quite different from what's already here, and this is one of
them." "Wherever it goes, it
causes strong reductions in small zooplankton," he added. "That will
have repercussions for the rest of the food web."
Pothoven said he knew the minute he saw the writhing
shrimp it was something new. He sent a species sample to a Caspian Sea species
expert in Duluth, Minn., who confirmed it as a freshwater shrimp that has been
invading its way across Western Europe during the past few years.
Pothoven said juveniles and mature females have been
found in the channel connecting Muskegon Lake to Lake Michigan, indicating that
the species is likely reproducing in the Great Lakes. If so, that apparently
brings the number of Great Lakes invaders to 183, and it probably won't be long
until No. 184 is found; for the past three decades a new exotic species has
been discovered in the Great Lakes, on average, about every 6½ months.
The majority of them are arriving in the lakes in the
accidental aquariums that are freighter ballast tanks. Ballast water is used to
stabilize a less-than-full cargo ship on the open seas. The problem is a ship's
ballast pump can suck in species along with water, and those organisms can be
set free when the ballast water is exchanged for cargo when a ship arrives in
the Great Lakes.
Since the early 1990s, Great Lakes-bound overseas
freighters have been required to exchange their ballast water in midocean. The
idea is to kill any freshwater organisms with salty water from the open
seas. But about 90% of overseas
freighters arrive in the Great Lakes laden with cargo, and have therefore
historically been exempt from the exchange law. Yet those "empty"
ballast tanks still hold residual pools as well as muck that can be teeming
with life.
"This just highlights the fact that we have not
successfully plugged the ballast water hole," said Reid.
But Reid says there is a bright spot. The Canadian
government began requiring overseas ships to flush their empty ballast tanks
with saltwater before entering the Seaway, and early studies show that is an
effective means of killing unwanted critters.