THE GREAT
TAKEOVER
56 DISCOVERMAGAZINE.COM
TOP: MYRIAH RICHERSON/USGS. OPPOSITE: NOAA
T
he first day of June 1988 was sunny,
hot and mostly calm — perfect weather
for the three young researchers from
Canada’s University of Windsor hunt-
ing for critters crawling across the
bottom of Lake St. Clair. A whining
outboard pushed the 16-foot-long runabout car-
rying Sonya Santavy, a freshly graduated biologist,
toward the middle of the lake that straddles the U.S.
and Canadian border.
On a map, Lake St. Clair looks like a 24-mile-
wide aneurysm in the river system east of Detroit
that connects Lake Huron to Lake Erie, and that is
essentially what it is. Water rushes quickly through
Lake St. Clair because it is as shallow as a swimming
pool in most places, except for a roughly 30-foot-
deep navigation channel down its middle. The U.S.
Army Corps of Engineers carved that pathway more
than half a century ago as part of the St. Lawrence
Seaway project to allow oceangoing freighters to sail
between Lake Erie and the lakes upstream from it.
When water levels were low or sediment high,
sometimes that channel still wasn’t deep enough,
forcing ships to lighten their loads to squeeze
through. This often meant dumping water from
the ship-steadying ballast tanks — water taken
onboard outside the Great Lakes. Water that could
be swarming with exotic life picked up at ports
across the planet.
As Santavy and her colleagues puttered over
a rocky-bottomed portion of Lake St. Clair, she
whimsically dropped her sampling scoop into the
cobble below. She was hunting for muck-loving
worms, but figured she’d take a poke into the rocks
below because — well, to this day, she still doesn’t
know. “I can’t even explain why it popped into my
head,” Santavy tells me.
Up came a wormless scoop of stones, the smallest
of which were not much bigger than her fingertips.
But there was something odd about two of those
tinier pebbles. They were stuck together. She tried to
pull them apart but she couldn’t. Then she realized
that one of them wasn’t a pebble at all. It was alive.
THE ZEBRA INVASION
Nobody gave it much thought at the time, but in
the years following the Seaway’s opening in 1959,
species not native to the Great Lakes, ranging
from algae to mollusks to fish, started turning up
at a rate never before seen. And the alien organ-
isms continued to arrive, year after year, with an
almost metronomic predictability — all the way
up to that steamy Wednesday morning on Lake
St. Clair in 1988.
Santavy showed a fellow scientist aboard the
research boat her living “stone.” It was obvious
to both of them that it was some kind of clam or
mussel, but the dime-sized mollusk looked like
Exotic mussels have pilfered the Great Lakes’ food supply,
creating a vast aquatic desert. BY DAN EGAN
actual size
