By GLENN GARNETT
They’ve crossed incredible distances stowed away on our ships. Once here, they multiply at an incredible rate, choking our habitat and muscling out native plant and animal species for food and space. Scientists say there’s no way we can hope to eliminate them.
A science fiction plot? A visit from your in-laws? No, we’re talking about something a little less sinister but no less serious. There are over 140 so-called "invading" species in the Great Lakes, non-native aquatic life and plants upsetting the eco-system and causing millions of dollars worth of damage a year to those of us at the top of the food chain. Almost half of these unwanted guests hitched a ride here in the ballast tanks of ocean-going vessels. And because they left their natural predators behind in the old country, the population of many of these species has skyrocketed largely unchecked.
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can grow to up to five centimetres in length. |
The most talked-about invading species in North America over the past decade has been the zebra mussel, or Dreissona polymorpha as they’re known to biologists. Actually, they took their sweet time getting here - originating in western Russia near the Caspian Sea, the widespread creation of canals and increasing commercial traffic introduced them to western Europe during the eighteenth century. The fresh-water mollusk was first discovered in these parts in 1988 in Lake St. Clair and today they’re found in each of the Great Lakes. In fact, scientists believe Lake Erie is home to the greatest concentration of these pests in the world.
Since then they’ve been very busy, now with untold billions of ‘em found in many parts of the Great Lakes, the St. Lawrence River as well as in some inland waterways in southern Ontario. Environmentalists fear zebra mussels could eventually spread to most bodies of water south of the Canadian Shield and into northern Ontario. Already zebra mussels have been spotted in lakes in the Muskokas, Kawarthas and along the Trent and Rideau waterway systems.
They’re getting inland courtesy of fishermen who unwittingly transport larvae in baitfish buckets, boaters who inadvertently picked up juvenile or adult mussels in larger lakes, and even scuba divers who transport unwashed equipment from one body of water to another.
As a diver who spends a few hours each summer visiting wrecks in the Great Lakes, I’ve noticed the mussel’s amazing propensity for encrusting everything in sight. I’ve also noticed that besides reupholstering the underwater landscape, the striped menaces have had another effect - the water is a lot clearer.
But according to Beth MacKay of the Ontario Federation of Anglers and Hunters, the dangers presented by zebra mussels are also clear.
"We’ve seen a lot of changes in the ecosystem as the result of zebra mussels," she says. "Some people think the water clarity caused by the zebra mussels is a good thing - that the species is cleaning the water. In fact they’re clearing the water of plankton which makes the water murky and that’s what fish feed on. The other problem with clearer water is that sunlight penetrates deeper, stimulating plant growth which can become a real burden to boaters and swimmers."
The reason for the spread is the zebra mussel’s amazing rate of reproduction: one female can crank out up to one million eggs a year. Once hatched, tiny zebra mussel "veligers" spread with the currents for two to three weeks until they locate your dock, your boat or your waterline. When the zebra mussel begin to form their familiar striped shells, they secrete fibres called byssal threads which virtually bolt them to any fixed object, including boat hulls, motors, rocks and your water intake line. Once in the line and firmly attached, water flow won’t dislodge them and eventually the line can get blocked completely. They can also make their way into the mechanical parts of your pumping system and affect the taste of your water.
Over the past ten years, industries and governments on both sides of the border have spent about $5 billion to control zebra mussels in water intake lines. A number of companies have sprung up recently with gadgets to forestall such an infestation. The Ontario ministries of Natural Resources and Environment say their brief testing has shown filtering devices to be more effective than magnetic or electrostatic gizmos.
Nature is taking its best shot at curbing the wild growth of the zebra mussels - native species ducks, catfish, and raccoons will chow down on ‘em, but it’s an all-you-can-eat buffet and the kitchen’s working overtime. Zebra mussels grow to about three centimetres in length usually have a lifespan of two to three years. A cousin of the zebra mussel, the quagga, also made its debut in the Great Lakes in the late ‘80s and has had a similar impact on the ecosystem but can survive in deeper and colder water.
Last year, another invading species, a small bottom-dwelling fish found around the world, made the news. And, at first blush, the arrival in the goby to the Great Lakes, a species of fish that feasts on the nearly ubiquitous zebra mussel, appeared to be a godsend. But MacKay begs to differ.
"Goby do eat zebra mussels but there’s a definite downside," she says. "Zebra mussels concentrate contaminants at a very high rate, the gobies feed on them and when native species of fish feed on the gobies, it’s passing contamination up the food chain. So, in fact this is causing contamination to enter the food chain at a must faster rate than would have normally occurred.
"The other downside with gobies is that they’re a very aggressive fish. They reproduce at a very high rate - most native fish only reproduce once in a season, whereas round gobies can reproduce multiple times."
While not as prolific as the zebra mussel, a female can produce up to 5,000 eggs in a season.
Another problem is that they’re claiming the turf of a number of native species including fellow bottom-dweller the skulpin. "We’re concerned that the population of the skulpin are being affected," MacKay says.
The rogues gallery of aquatic butt-inskis include a bunch of fish you’ve probably never heard of, including the ruffe, the rudd and the threespine stickleback which is about as attractive as it sounds and not good eatin’ at all.
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the spread of invading species. |
What can be done to get these villains on the last stage out of Dodge? Unfortunately, there appears to be no magic bullet - scientists say containment is the only answer.
"I think the key solution is to make sure that we don’t spread them to new areas," MacKay says. "We’ve established guidelines for people involved in recreational water activities, whether it’s boating, scuba diving or fishing. Because once a species like zebra mussels take hold, they’re there to stay. So by preventing the spread, we’re containing the impact on the environment as a whole."
The Ontario Federation of Anglers and Hunters says lakeside cottagers concerned about the spread of zebra mussels should regularly inspect their shorelines and the intake end of intake pipes for early signs of zebra mussels. They recommend that you fix a rope to the end of your dock dropped into the water which you can inspect occasionally for signs of unwanted visitors.
"We have a volunteer monitoring program whereby cottage associations and those who live by the water can borrow our kits to sample their water and send the samples back to us so we can check for zebra mussel veligers (larvae) which are microscopic," MacKay says.
For more information on zebra mussels and what to do about them, call the Invading Species Hotline at 1-800-563-7711.
