TIME: Almanac 1993/TIME Almanac 1993.iso/time/012191/0121340.000

Text File | 1992-08-28 | 5.4 KB | 117 lines

                                                                                NATURE, Page 63

Invasion of the Zebra Mussels


They could be coming soon to a river or lake near you

By J. MADELEINE NASH/MONROE


    In a B movie, a marauding mollusk would probably be played
by a giant clam. But the real-life monster swimming amuck in
the Great Lakes is a tiny creature the size of a fingernail.
With its jaunty brown stripes, a solitary zebra mussel looks
cute, not threatening. The trouble is that the animal is
anything but a loner, and its tendency to form colonies of
thousands, even millions, makes it threatening indeed.

    Unknown in North America until 1988, the zebra mussel has
become a pest whose exploding population has prompted alarming
predictions of millions of dollars' worth of damage to
water-supply systems and the ruination of the sport-fishing
industry. A year ago, the city of Monroe, Mich., lost its water
supply for two full days because intake lines were plugged with
zebra mussels. Earlier, Ford Motor's casting plant in Windsor,
Ont., found the creatures choking off the flow of cooling water
to its furnaces. Boaters, meanwhile, have watched their hulls
and engines become encrusted with mussels.

    Native to the Caspian Sea region of the Soviet Union, the
zebra mussel spread into the canals, rivers and lakes of
Western Europe more than 150 years ago. Then sometime in 1986,
biologists speculate, a European cargo ship bound for Sarnia,
Ont., emptied some of the water it carried as ballast into Lake
St. Clair, between Lake Huron and Lake Erie. Biologists first
spotted a few zebra mussels in the area three years ago -- and
the race was on.

    Every year each female mussel produces approximately 30,000
eggs. When fertilized, these eggs hatch into microscopic larvae
that swirl with the current. Eventually the larvae find a
surface to their liking and settle down, mooring themselves
with sticky, hairlike threads called byssuses. They reach
sexual maturity in massive colonies that pack as many mussels
into a square meter as there are inhabitants in a midsize town.

    Virtually unchallenged by natural predators, billions of
zebra-mussel larvae left their initial colonies in Lake St.
Clair and Lake Erie and drifted into Lake Ontario. By attaching
themselves to boats, some adventuresome mussels even managed
to move upstream into Lake Huron, Lake Michigan and Lake
Superior. Similar outriders are expected to start showing up
in smaller lakes and major rivers such as the Mississippi, the
Susquehanna and the Hudson. "Within 20 years," predicts
Margaret Dochoda, a biologist with the Great Lakes Fishery
Commission, "the zebra mussel will likely have taken the entire
East Coast of the U.S."

    For utilities and industries, the zebra mussel represents
one of the biggest maintenance challenges next to corrosion.
Detroit Edison, for example, has spent $500,000 cleaning the
critters from the cooling system of its Monroe power plant.
"Our plant," says superintendent Sam Smolinski, "has turned
into a zebra-mussel nursery. Frankly, we can't fathom things
getting any worse."

    Foreign organisms have invaded the Great Lakes before, but
few have engendered such apprehension. "The zebra mussel is a
keystone species," says zoologist David Garton of Ohio State
University. "It has the power to restructure the entire
ecological community." The zebra mussel can strip water of
algae and other microscopic plants and thus endanger animal
life. Native clams are beginning to die off, victims of the
zebra mussels' habit of attaching to clamshells in such numbers
that they cannot open.

    Still, with a little luck (and an increase in predation by
native fish like the fresh water drum), the zebra mussel may
yet be brought under control. In fact, some evidence suggests
that the mussel population in Lake Erie may have peaked. "There
are many ways to kill the zebra mussel," observes Ohio State
entomologist Susan Fisher. "The trick is to do it selectively"
without wiping out other aquatic life. Fisher has recently
found that minute traces of potassium, nontoxic to other
organisms, reliably send zebra mussels into fatal shock. Paints
laced with potassium, she speculates, might protect underwater
structures from mussel infestation. Physiologist Jeffrey Ram
of Wayne State University in Detroit makes an even more devious
suggestion. Zebra-mussel spawning, he notes, is triggered by
odors wafting from phytoplankton. These chemical cues ensure
that the eggs hatch when the food supply is plentiful. But what
if synthetic scents were dabbled like perfume above the mussel
beds? A premature spawn, says Ram, would surely doom most of
the larvae.

    "I do not understand this talk of killing," counters
biologist Anna Stanczkowska-Piotrowska of Poland's
Agricultural-Pedagogical University. The zebra mussel, she
points out, is not without virtues. Its byssuses extrude an
adhesive that may have commercial value. Its appetite for
foul-smelling algae can markedly sweeten the taste of drinking
water. Perhaps most admirable of all, the zebra mussel has
performed an act of public service by dramatizing the threat
posed by tiny organisms that hitch rides around the world. Both
the U.S. and Canada are moving to restrict the discharge of
ballast water into the Great Lakes, a measure of ecological
prudence that is long overdue.