Who Loses When Aliens Invade a Lake?
Posted February 1, 1998
Are there really aliens out there? There may not be aliens from space, but there are certainly organisms that are alien to their ecosystems. These alien species are
organisms that move from their normal environment into a new environment. Sometimes the introduced species move into new environments on their own. Armadillos, for example, began an
invasion of the southern United States from Central and South America on their own a few decades ago. But usually species are introduced either by accident or by intention. Rabbits were
introduced to Australia on purpose. Fire ants arrived in Mobile, Alabama, aboard a banana boat.
Introduced species can have devastating impacts upon local ecosystems. Often they have no natural predators in the new environment, so their populations explode.
This leads to competition with native species for food, water, and living space. Sometimes the introduced species out-competes the native species, leading to their extinction. This type
of invasion is occurring right now in the Great Lakes of the United States.
Zebra mussels were brought into the Great Lakes in the water used as ballast on ships. When ships released their ballast water into the lakes, the tiny zebra mussels
were released as well. Within a few years, the zebra mussel population had exploded. Zebra mussels clogged the intake pipes of water facilities and the discharge pipes of wastewater
treatment plants. They also attacked native clam species. By the mid-1990s, native clams in Lake Erie had almost vanished.
Fortunately, scientists have found that several species of native clams have escaped the invasion in the marshlands surrounding Lake Erie. Much of the bottom of Lake
Erie consists of sand and gravel sediments. Clams covered with zebra mussels cannot burrow very far into these soils. But clams covered with mussels can bury themselves completely in
the soft sediments found in marshlands. By burrowing completely, the clams killed their attached zebra mussels. Scientists discovered representatives of more than 20 species of native
clams in these marshland sediments.
What will be the eventual outcome for the invading zebra mussels and the native clams? Some scientists predict an eventual decline in the zebra mussel population.
Others suggest that a widespread plan of attack will be necessary to turn back the invaders. If and when this occurs, the clam species that burrowed into areas with soft sediments may
become the brood stock to repopulate the Great Lakes with native clams.
Nichols, S. Jerrine and Douglas A. Wilcox. "Burrowing Saves Lake Erie Clams." Nature, October 30, 1997, Vol. 389, No. 6654, p. 921.