Eyewitness
Account of Presque Isle Invasion
The Damage A Zebra Mussel Can Do
by Charles Bier, Director, Natural Heritage, WPC
". . . they were becoming lifeless and dying by the droves … this was an ecological bench-mark for the continent."
I
remember walking across the moist sand hoping it was not true. The gulls
were circling and clamoring as they always do along the beaches of Presque
Isle, and Saturday, October 6, 1990, was no different. I had one small
hand of each of my children wrapped in mine as we trudged along toward
what I was told would be a morbid destination. Their gazes were constantly
upward at the gulls, while mine was straight ahead toward what I had been
told was a biological catastrophe.
Birdwatchers are an accurate bunch and I didn't have any real doubt about
this report. I had received a call a few days before from members of the
Presque Isle Audubon Society, just after a severe late summer storm crashed
into the peninsula from the northwest. These fellow conservationists knew
I had spent the previous seven years working with other biologists to
assess the status of freshwater mussels in Pennsylvania. They also knew
of the various times I had trekked across the beaches of this state park
looking for evidence of the mussels inhabiting Lake Erie, and they knew
that after countless hours of scanning the sands, few shells were ever
found. That was about to change.
The
last sand dune no longer blocked our view and we had a clear picture up
the beach toward Gull Point. There they were, by the thousands. Thousands
of fist-sized freshwater mussels from Lake Erie were strewn across the
beach and sandflats. But they were not alone. Attached to the end of each
of their shells was the causal factor: Dressina polymorpha, the zebra
mussel.
How many similar storms had passed across Lake Erie over the millennia
with no such impact? Storms that the mussels knew well and had long ago
become adapted to survive. But starting three or four years earlier, with
the introduction of the zebra mussel into the lake (mid-1980s), storm
survival was now a new challenge. All I could think about was how they
were becoming lifeless and dying by the droves … this was an ecological
benchmark for the continent.
Dense clusters of zebra mussels were tenaciously attached to the end of
each of the native mussel's shell. Although each zebra mussel was only
half an inch long, the dozens glued to each native mussel's shell (and
to each other) created a mass as large, or larger, than the three-to-five-inch-long
native. These clusters were extra baggage for the natives, and they were
prevented from burying deeper in the lake bottom as the storm waves intensified.
The kids ran up the beach to the edge of the disaster and stared down
at their feet. They knew mussels, having been along on field trips to
inventory living populations. They knew the mussels were supposed to be
in the water, not on the parched sands. It appeared as though some of
the mussels were still holding on, and the children were now collecting
and tossing them back to the lake to undo the impact of the invader. Others
had clearly expired, evidenced by gaping shells and spongy protruding
feet.
Although my interest was to witness this remarkable event, I was also
here for statistics. A total count was not possible. The bodies ran up
the beach for hundreds of yards. I listed the species: three-ridge, giant
floater, spike, Wabash pigtoe, fat mucket, fragile papershell, eastern
pondmussel and pink heelsplitter. By far the most abundant mussel was
the fat mucket (Lampsilis siliquoidea). We collected a representative
sample to document the horrid event for natural history museums. Ohio
State University reported back that we had deposited 174 dead fat muckets,
with zebra mussels still attached. A similar lot went to the Academy of
Natural Sciences of Philadelphia. Others I kept as part of Western Pennsylvania
Conservancy's educational collection. Still, these collections were no
percentage of the masses that remained.
We witness the acts of nature all the time, but some are never to be repeated
and this was one of those. Lake Erie would (probably) never be the same
again. The zebra mussel has gone on to be a major threat to the conservation
and management of our native freshwater mussel resources, especially in
some cases for species already endangered, as it has escaped the Great
Lakes and moved to inland rivers. I don't think my children understood
the significance of that afternoon, and I'm not sure burdening them with
the scientific gloom of it would have been appropriate either.
Nonetheless, the image is stuck in our minds.
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