There is good cause to fear another threat poised to strike Lake Winnipeg and wreak untold havoc upon the lake’s ecosystem.
Phosphorus overload, creating massive algae blooms easily seen in satellite photographs, has already alarmed scientists, politicians and the public, who fear that the burden will overwhelm the lake and transform it into a dead zone.
Just across the American border in North Dakota, looms another threat — the zebra mussel, a tiny and deadly invasive species first found in large numbers in the Great Lakes.
Last September, the mussel was found by a local resident at Pelican Lake, Minnesota, about 800 kilometres south of the Manitoba border. Now, zebra mussel larvae have been 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 is a mere 635-kilometre leisurely drift on river currents for the larvae to reach Emerson at the U.S.-Canada border.
“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 Manitoba Water Stewardship Minister Christine Melnick, when the zebra mussel threat was detected in 2009.
“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.”
The presence of zebra mussels, a species of mussel native to Eastern Europe and Western Asia, was first noticed in North America in Lake St. Claire, near Detroit, Michigan, in 1988. It is believed mussel larvae hitched a ride from Europe 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 spread to the Hudson River in New York and as far west as California and as far south as Florida.
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, 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 five-centimetre-long (fingernail size) zebra 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 people had to boil drinking water in their homes until the normal flow was restored a few days later.
Researchers and scientists 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, disruption of the food-chain by zebra mussels could destroy the lake’s valuable commercial and recreational fishing industries. According to the Manitoba government, commercial fishing, which is primarily based in Lake Winnipeg, provides income and a way of life for nearly 3,500 Manitobans. In 2004-05, the Manitoba Water Stewardship Annual Report said the annual commercial harvest has averaged about 13-million kilograms (28.6-million pounds) per year since 1994. In dollar terms, this represents nearly $25 million a year that is invested back into Manitoba’s economy.
In addition, Microcystis algae has been spreading in Lake Winnipeg, especially in the north basin. Hundreds of square kilometres of gooey blue-green algae blooms have been noted in the north basin as well as the south basin in recent years. In 2003, Microcystis caused the closure of Victoria Beach, although the south basin’s murky water prevents sunlight penetrating to any great depth (the north basin is deeper and its water is clearer), which is what helps slow the growth of blue-green algae. Since blue-green 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.
As an invasive species, zebra mussels have no native predators other than small- and large-mouth bass, which cannot eat enough mussels to make a significant dent in their numbers.
Zebra mussels are a sinister threat that should instill fear in Manitobans. 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.
No one can predict the exact outcome of a zebra mussel invasion of 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.