It’s not a composite creature like Frankenstein. It’s more like Dracula, who’ll suck the lifeblood out of a hapless victim. But it’s no legendry horror of Hollywood or Halloween mythology. A real monster is poised to suck the lifeblood out of Lake Winnipeg’s ecosystem. Manitoba Conservation and Water Stewardship confirmed in mid-October that zebra mussels had been found in provincial waters. The tiny filter-feeders were discovered clinging to the hull of a private boat and a dock at Winnipeg Beach, and on some fishing boats dry docked at Gimli.
It was just a couple of years ago that zebra mussels, a tiny and deadly invasive species, were reported to be just across the international border in North Dakota. Earlier, the mussels were found by a local resident at Pelican Lake, Minnesota, about 800 kilometres south of the border. Then zebra mussel larvae were reported to have progressed from Minnesota to North Dakota into the Red River at Wahpeton, where the river begins its northward journey to Lake Winnipeg. It was a mere 635-kilometre leisurely drift on river currents for the larvae to reach Emerson at the U.S.-Canada border.
How the mussels actually made their way into Lake Winnipeg is still a matter of speculation. Since adult zebra mussels can survive out of water for several days or weeks if the temperature is low and humidity is high, they could have been transported on a boat’s hull after it was used in mussel-infected waters, or the larvae could have drifted into Manitoba. Whatever the scenario, they’re here, they’re alive and they’re an extremely serious threat to the lake.
“Zebra mussels have caused millions of dollars in damage (actually, billions) to the Laurentian Great Lakes area and are a significant environmental and economic concern to Manitoba,” said then Water Stewardship Minister Christine Melnick, when the zebra mussel threat was first detected in North Dakota.
“While Manitoba has been proactive in recognizing and planning for the potential threat of zebra mussels, this new discovery makes it imperative that the public is well informed,” she added. “Public education is key to reducing the spread of zebra mussels in Manitoba. Boaters must take appropriate measures to clean their boats before moving them between water bodies.”
That was the warning, but it still didn’t prevent zebra mussels from invading Manitoba.
The presence of zebra mussels, a species of native to southern Russia, was first noticed in North America in Lake St. Claire, near Detroit, Michigan, in 1988. It is believed mussel larvae hitched a ride in the ballast water of a transoceanic ship. Having gone down the St. Lawrence River and through the manmade locks to the Great Lakes, a ship emptied its ballast, discharging the microscopic larvae and forever changed the freshwater ecosystem of the region. Since that fateful discharge, zebra mussels have rapidly spread across North America.
A female mussel can spawn one-million larvae (called veligers) each year. The prolific and plankton-devouring mussel uses a special byssal gland to secrete highly-adhesive threads that attach it to rocks, debris, water pipes, fishing nets, boat hulls and native mussel species. The attachment ability of the mussels results in bio-fouling — masses of mussels clogging pipes and choking off oxygen and the food supply of other organisms.
The residents of Munroe, Michigan, on December 14, 1989, were the first to witness the threat posed by the fingernail-size mussels when the creatures, combined with icy conditions, blocked off the city’s Lake Erie water intake. Schools, restaurants and factories were forced to close down and residents had to boil drinking water until the normal flow was restored a few days later.
Researchers from the Great Lakes Environmental Laboratory in Ann Arbor, Michigan, documented basic changes in the food-chain in the zebra-mussel-infested waters of Lake Huron’s Saginaw Bay. According to the research by the U.S. National Oceanic and Atmospheric Administration-run laboratory (NOAA), Saginaw Bay’s energy base is no longer dominated by phytoplankton because the microscopic free-floating plant cells are the choice food for zebra mussels, which are able to selectively filter the cells out of the water.
A press release by the NOAA said, “The spread and growth of zebra mussels have decimated this important free-floating part of the food-chain, raising concerns that all of the bay’s fish stocks may suffer.”
Zebra mussels may also release nutrients that encourage algae growth, especially toxic blue-green algae, according to the NOAA lab. Certain forms of a blue-green algae named Microcystis are toxic to fish and cause gastro-intestinal distress in humans. In Lake Winnipeg, hundreds of square kilometres of gooey blue-green algae blooms have been noted in the north and south basins in recent years. Since the algae is toxic, it isn’t consumed by tiny fish that are part of the native food chain, and as a result the blooms grow throughout the summer. While the toxins secreted by the algae stress native species of mussels, a study has found that zebra mussels are unaffected; thus, they have a free rein to outcompete their competition.
The disruption of the food-chain by zebra mussels has the potential to destroy Lake Winnipeg’s commercial and recreational fishing industries. Commercial fishing, which is primarily based in Lake Winnipeg, provides an income and a way of life for nearly 3,500 Manitobans. The annual commercial harvest has averaged about 13-million kilograms per year. In dollar terms, this represents nearly $25 million a year that is invested back into Manitoba’s economy. Another potential blow to the local economy is that the mussels can foul recreational beaches.
As an invasive species, zebra mussels have no native predators other than small- and large-mouth bass and crayfish, which cannot eat enough mussels to make a significant dent in their numbers.
The only potential check upon their northward journey is that female mussels cannot breed in water temperatures below 12°C, although warmer water is found each summer in the south basin of Lake Winnipeg. Global warming could also make a good-sized chunk of Manitoba prime zebra mussel habitat.
Manitoba Conservation and Water Stewardship did react quickly to the first reports of the invasion, implementing a rapid-response protocol that sent staff to communities on the west side of the lake to collect samples to determine the extent of the invasion, deployed mobile decontamination units, and informed boat owners and others of the threat. The staff will be at the scene of the invasion until freeze-up.
As yet, no one can predict the exact outcome of the invasion on Manitoba’s lakes and rivers, but the experience in other jurisdictions has shown ecological changes that are bad for commercial and recreational fishing as well as tourism, which is a cause for grave concern in our freshwater-rich province.