Invasive mussels killing Great Lakes from the bottom up

When a freighter ditched its ballast water in the Great Lakes more than 20 years ago, it triggered a deadly invasion.

When a European freighter ditched its ballast water in the Great Lakes more than 20 years ago, it triggered a deadly alien invasion. Today, that invasion has cost the lives of untold millions as well as costing billions of dollars to the economies of Canada and the United States. And it is all happening underwater.

The first of the invaders were the small zebra mussels, discovered in 1988 in Lake St Clair, a small body of water between Lake Erie and Lake Huron. Not long afterwards, they were joined by the quagga mussel. The ecosystem of the Great Lakes began to change, probably irrevocably. Native fish and algae began to die out as the zebra mussels, which attach themselves to rocks, filtered out the minuscule vegetation - phytoplankton - on which the whole ecology of the lakes is based.

And while the zebras covered the rocks, the quagga mussels began colonising the sandy bottoms with similar results. The boulders that covered the bottom of Lake Michigan for centuries, for instance, have now disappeared under a carpet of mussels and primitive plant life, while native species of fish have been starved out of existence. The mussels have now spread to other lakes in Canada and to more than 20 US states after hitching rides on pleasure boats. In the Great Lakes themselves, the problems originally experienced in Lake Erie are now being replicated in the upper Great Lakes - Michigan, Huron and Superior - where the population has tripled in the past three years as the zebra mussels adapt to colder, deeper waters.

While local lake trout, salmon and whitefish become scarcer and skinnier, the one beneficiary has been the population of round gobies - another invasive species from the Black Sea - who thrive on the mussels, breed prolifically and are now the most abundant fish species found in parts of the lakes. "We don't necessarily know all the impacts, but we know enough to know that they are being catastrophic," said Cameron Davis, president of the Alliance for the Great Lakes. "The ecological balance of the Great Lakes is at a tipping point. And the question is: can they recover? Or can we act quickly enough to help them recover?"

Environmentalists are hoping that the US Senate will approve a bill, already passed by the house, ordering freighters to install systems for killing invasive fish, mussels and other creatures that harm the Great Lakes' ecosystem. However, the bill appears to be bogged down this week in a row over its implications nationwide between Barbara Boxer, a Democratic senator from California and chairman of the environment and public works committee, and Daniel Inouye, a Hawaii Democrat and chairman of the Commerce, Science and Transportation Committee.

In 2006, Canada instituted new regulations requiring ships preparing to enter the Great Lakes to flush their ballast tanks with salt water at least 320km offshore. The United States followed suit this year, affecting about 500 vessels a year using the St Lawrence Seaway. "We applaud the new measures," said Jennifer Nalbone, a spokesman for Great Lakes United, an environmental group based in Montreal. "But the studies also show that it won't stop all invasive species from coming into the Great Lakes. It isn't the final solution."

A report from the University of Notre Dame put the cost to the regional US economy of foreign species in the Great Lakes at more than US$200 million (Dh734m) a year. Sport fishing has suffered the biggest loss, with participationfalling as much as 35 per cent because of the declining fish populations. Commercial fishing, wildlife tourism and even water extraction by municipalities have also taken big hits.

Now global warming is threatening to worsen the problem. If water temperatures increase even slightly in the winter months, the mussels will be able to maintain peak activity all year, consuming nutrients at an even more alarming rate, Henry Vanderploeg, a scientist from the National Oceanic and Atmospheric Administration, said at conference at the University of Michigan this week. "We've got a mess," he said. "And then you add warming of the system to this ... it isn't going to help."

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