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A handful of zebra mussels (John L. Russell)
A handful of zebra mussels (John L. Russell)

How a European cargo ship kills a Great Lakes loon Add to ...

Two years ago, a tiny shrimp-like creature with a creepy name - the bloody red mysid - was discovered in Lake Ontario, the latest in a long line of foreign invaders believed to have arrived by cargo ship through the St. Lawrence Seaway.

Ravenous, it travels in packs and upsets the food chain wherever it takes up residence. It's still too early to predict how much damage the bloody red mysid will do to its new home, but scientists aren't about to rule out the worst.

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They know this from experience. Here is how researchers believe that one early interloper, travelling in the belly of a boat from another continent, has led to thousands of loons washing up dead on the shores of the Great Lakes.

1. A freighter leaves a European port, bound for ports such as Duluth, Minn., on the southwest shore of Lake Superior, or Thunder Bay, to the north. Sloshing around in the bowel of the ship is a muddy mix of sand and water - the ballast used to maintain the vessel's stability as it traverses the oceans. The amount of ballast depends on how much cargo the ship is carrying, but even fully loaded ships that technically need "no ballast on board" - called NoBObs - still have some leftover slop in their tanks. Foreign freshwater species from ports near rivers are pumped in with the water, and because of faster travel times, they survive the ocean crossing. On one occasion at least - but probably many more times - the stowaway is a striped, freshwater mollusk, the quagga mussel, or its cousin, the zebra mussel.

2. The freighter makesit way up the St. Lawrence, through the locks and canals, usually offloading its cargo at ports such as Hamilton as it moves west through the system into Lake Superior, dumping its ballast as needed. Sometimes the foreign marine life dies: The season is off, or its numbers are too small, or the location proves inhospitable. "An invasion is a roulette wheel spin," says Anthony Ricciardi, a biologist at McGill University in Montreal. "You may not get in on the first try, but keep trying and you get in."

This time, the species gets in, and flourishes. Soon, zebra mussels, first discovered in Lake St. Clair, have hopped into the other lakes, carried by other ballast loads or hitching a ride on the hulls of various boats.

3. Zebra mussels spread like a contagion across the lake bottom, sucking life out of the water, filtering everything around them. They probably breed undiscovered for a decade or more. To boaters above, the lakes seem clearer, when, in fact, a deathly brew is stewing. With more light and the waters warming, weedy algae called Cladophora begin to grow. (The algae do their own damage: In 2007, weeds clogged intake pipes and forced a nuclear-power plant in New York State to close three times.)

4. When the algae die and decompose, they suck oxygen out of the water, and in that environment, the botulism bacteria thrives. It, in turn, is sucked up by the voracious quagga and zebra mussels.

5. The only fishthat eats the mussels is itself a non-native - the round goby, an aggressive bottom-dweller that scientists believe also was probably introduced by transoceanic ships in the early 1990s.

6. The goby eats the botulism-carrying mussels and then along comes the loon, fishing for its dinner. The goby, especially if it is sick and slowed by the bacteria in its system, makes for an easy catch. The botulism spreads to the loon.

7. The loon dies , to be found belly-up on shore.

Scientists call this "invasional meltdown." Since the St. Lawrence Seaway opened, 57 non-native species are believed to have invaded the Great Lakes through the ballast of ocean-crossing ships. New regulations require all ships to flush out their tanks before entering, but biologists point out that, unlike chemical spills, it takes only one ballast dump to introduce an environmentally disastrous life form.

Scientists such as Dr. Ricciardi are now watching for the arrival of another species dubbed the "killer shrimp" - which is tiny and insatiable, and snacks on much larger creatures. "It's an amazing little beast," he says. "That one might cause trouble if it gets over here."

How much trouble, scientists can't be certain. After all, when zebra mussels were discovered in 1988, no one was thinking of loons belly-up in 2007.

"Who could have predicted that?" Dr. Ricciardi asks. "We can figure it out now, we think. But risks assessment of the zebra mussel would never have considered that. You put some invaders together, you change some conditions around, you mix it all together and you get this witches' brew that leads to ecological surprises like this."

 

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