The Great Lakes have battled invasive species for better than a half century, and over time new threats have been multiplying as international trade brings more water-borne species in from around the globe in the ballasts of ships. Over the past decade, the zebra mussel has leapt to the top of the list in terms of its impact on Great Lakes ecology.
Now researchers believe it is being bumped off—quickly, and menacingly—by its smaller cousin, the quagga mussel. Though just the size of a fingernail, it has characteristics that could pose a grave threat. The quagga and zebra wreak havoc in essentially the same way: They remove critical plankton from the water—the first link in the Great Lakes food chain—and the ecological shock works its way up. Their prolific breeding also gums up most any intake pipe for utilities and other water-dependent industries.
Where the quagga mussel separates itself—and represents an added threat—is that it can survive in much deeper and colder water than the zebra mussel, which depends on warmer water, keeping mostly to rocky shore areas. Recent samples have shown that the quagga is already devastating the zebra mussel in its own territory, and has also been discovered thriving at depths of 300 feet and found as deep as 540 feet.
—Ronald A. Wirtz
