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Adaptive Aliens:
Invasive Species Threaten Lake Ontario
The tail of the spiny water flea is sharp
- too sharp to swallow. The appetite of
the Asian carp is enormous. Zebra mussels
will stick to just about anything, the sea
lamprey's suction cup mouths drains the
lifeblood from salmon and trout, and the
homely, rugged little round goby is like
the wolverine of the water world, ferociously
fending off all threats to food and territory.
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Alien Aquatic Species Be Stopped?
Great Lakes regulatory bodies
such as the International Joint
Commission have identified invasive
species as a significant threat
to the health of the Great Lakes
ecosystem, along with excess
nutrients, toxic contaminants,
habitat destruction, and airborne
pollution. Some scientists have
suggested that the only way
to protect the Great Lakes from
further invasive attacks is
to isolate them - by closing
the St. Lawrence Seaway. Proposals
for less extreme measures of
control include physical barriers
(such as traps and electrical
devices), stricter monitoring
and enforcement of ballast water
regulations, and a significant
investment in ballast water
treatment technologies such
as filtration, heat and ultraviolet
light.
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No matter what their origin -foreign freighter
or domestic bait bucket - each of the non-native
species that is threatening the balance
of the Lake Ontario ecosystem has at least
one highly adaptive mechanism that has allowed
it to flourish in its new environment:
The Zebra Mussel
- Drop just about any hard object
into the waters of the Bay of Quinte, in
the eastern end of Lake Ontario. Wait a
month, and pull it back out. Chances are
it will be coated with hundreds of fingernail-sized
zebra mussels. The prolific mussel, with
a voracious appetite for plankton, uses
a special byssal gland to secrete highly
adhesive threads that attach it to rocks,
debris, water- pipes and screens, boat hulls,
and - most destructively - native mussels.
The zebra mussel's remarkable attachment
ability causes bio-fouling, or build-up
of masses of mussels (and mucous-like mussel
excrement), that can clog pipes and choke
off oxygen and food supplies to other organisms.
The mussel also reproduces quickly, and
filters vast quantities of water, monopolizing
the phytoplankton that formerly sustained
other aquatic life (see "Disappearing
Diporeia" in this section). Normally
a freshwater organism, the zebra mussel
has even shown signs of being able to survive
the slightly salty conditions of the lower
St. Lawrence River.
The adverse ecological effects of zebra
mussels are not limited to physical smothering
and bothersome blockages. Toxic contaminants,
such as PCBs and PAHs, are heavily concentrated
in the tissues of the ubiquitous bottom-dwellers,
and excreted in dangerously high amounts
in their feces. Through the process of bio-magnification,
ever-increasing concentrations of pollutants
are passed up through the food chain, to
sport fish, waterfowl and humans. Zebra
mussels are also being implicated in Great
Lakes outbreaks of bottom-dwelling botulism
(see "The Big Flip" in this section).
Even the sharpness of their shells is causing
problems for hungry fish trying to digest
them, and for barefoot swimmers wading through
mussel-infested waters.
Since the mussels arrived in the ballast
water of Eurasian transoceanic vessels,
about 20 years ago, Great Lakes scientists
have been trying to halt their spread. Limited
use of chlorine - at power plants and water-intake
pipes - has been successful, but is not
appropriate in larger applications.
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