Quagga mussels taking over Great Lakes
DETROIT – There’s a new boss on the Great Lakes, controlling the food web in ways that impact virtually every living thing that swims or crawls in them.
Quagga mussels, the thumb-sized, clumping mollusks that invaded the Great Lakes in the 1990s, have proliferated to dominate the lower four Great Lakes – connected lakes Michigan and Huron, Lake Erie and Lake Ontario. While scientists have understood the quaggas impact the nutrients essential to Great Lakes ecology in near-shore regions of the lake, a new study shows just how profound and widespread that impact really is.
Researchers at the University of Minnesota-duluth’s Large Lakes Observatory, in a new study, examined whether the quagga mussels have altered the cycle of phosphorus, a key mineral that serves as a regulator of Great Lakes ecology, throughout the entirety of the lower four Great Lakes. Their research found it has.
The quaggas’ outsize role in the lakes’ nutrient loads has ramifications for the smallest aquatic organisms up to the large sport fish that fuel a $7 billion annual Great Lakes fishery. It also frustrates human efforts to better control and regulate nutrient flows into the Great Lakes that can cause algae blooms and oxygen-deprived dead areas.
To understand how profound and unlikely it is that a small shellfish can control phosphorus loads in all of four Great Lakes, consider the size of those water bodies. Lakes Michigan, Huron, Erie and Ontario combined contain 3 quadrillion gallons of water. A quadrillion is a million million, multiplied by 1,000. Jiying Li, a postdoctoral researcher on, and co-author of, the Minnesota-duluth study, explained the focus on phosphorus.
“Phosphorus is the limiting nutrient – it controls biological production in the Great Lakes,” said Li, now an associate professor in the Department of Ocean
Science at the Hong Kong University of Science and Technology. “When there’s too little, there’s no fish, no production, because this is an essential nutrient. And too much is not good; there will be algae blooms.”
It also matters where the phosphorus is in the lakes, said study co-author Sergei Katsev, who studies freshwater ecosystems at the Large Lakes Observatory.
“At the early stages of the quagga invasion, when they colonized just the shallow areas, they were basically pulling phosphorus to near-shore, and there were algal blooms” as a result, he said. “While offshore was getting really, really low on phosphorus, the nearshore was getting enriched. That picture is gone now. The quagga mussels are spread all over the lakes.”
And if that biomass of mussels changes only a little, it means large fluctuations in the phosphorus in the water column because of the amount the shellfish are storing inside their bodies at any given time, he said.
Almost three decades after being discovered in Lake St. Clair, likely arriving in the ballast water of freighters that traveled through eastern Europe, quagga and related zebra mussels spread throughout the Great Lakes and most major river systems in the eastern U.S. As both types of mussels outcompeted native species, quagga mussels eventually outcompeted zebra mussels as well, and are now the dominant invader found around the Great Lakes.
Growing up to 2 inches in size, the quagga mussels reproduce quickly, eat voraciously and clump together, clinging to almost anything in the water.
They have all but crowded out native clam species and have disrupted the base of the aquatic food chain – vacuuming up the tiniest plants and animals. That has ripple effects all the way up the aquatic food chain, to iconic sport fish such as salmon and lake trout, Li said.
“The big fish eat the small fish, and the small fish eat the algae and zooplankton,” she said.
Zebra and quagga mussels also cost industries, businesses and communities $5 billion between 1993 and 1999 by clogging water intake pipes, according to congressional research, with $3.1 billion of that cost coming from the power industry alone.
The U.S. and Canada helped turn around Great Lakes water quality – particularly on Lake Erie, which was declared all but dead in the 1970s because of choking nutrient overloads and other pollution – through phosphorus reduction efforts. A nationwide voluntary ban on phosphates in laundry detergents was enacted in 1994, and 17 U.S. states, including all of the Great Lakes states, enacted similar restrictions on phosphates in dish detergent in 2010. Farmers and environmental managers have also worked to reduce the runoff of fertilizers, including phosphorus, into Great Lakes tributaries.
“We would say, ‘If we keep the load below those target numbers, we will prevent algal blooms,’ ” Katsev said. “Now we seem to be losing the effectiveness of this tool. Mussels have greater influence.”
That means environmental managers “will need to make better models,” and more needs to be understood about quagga mussels and where and how their populations are expanding in the Great Lakes, he said.
The sheer numbers of quagga mussels left an impression on Katsev, he said. At one point, the scientists lowered a camera with a light almost 200 feet to the Lake Michigan bottom. They could see images of the quagga mussels, but the picture wasn’t the best.