THE LOTKE-VOLTERRA CRASH IS COMING.

Opening the Great Lakes to ocean shipping never delivered much by way of commercial benefit, although it delivered a lot of invasive species.  What happens, though, when the invader mussels strain out all the plankton?

In analyzing satellite images between 1998 and 2012, researchers at the Michigan Tech Research Institute were surprised to find that lakes Michigan and Huron are now clearer than Lake Superior. In a study published late last year, the researchers say limiting the amount of agricultural and sewage runoff in the lake has had an immense impact. However, the emergence of invasive mussels, which number in the trillions and have the ability to filter the entire volume of Lake Michigan in four to six days, has had an even greater effect.

“When you look at the scientific terms, we are approaching some oceanic values,” said Michael Sayers, a research engineer at Michigan Tech and co-author of the study. “We have some ways to go, but we are getting a lot closer to Lake Tahoe. A lot of times, you’ll hear from people that the water is so blue it compares to something in tropical areas.”

While appealing, the clarity comes at a significant cost to wildlife. In filtering the lake, the mussels have decimated the phytoplankton, a single-celled, green algae that serves as the base of the food chain. For much of the past decade, prey fish, like alewives, have remained at historic lows, prompting state managers to scale back the annual stocks of prized predators, such as king salmon.

The startling evolution has called into question the future of Great Lakes marine life and the region’s $7 billion fishing industry.

“Clearer is not necessarily better,” said Robert Shuchman, co-director of the Michigan Tech Research Institute. “Clearer water means less phytoplankton in the water column, and they’re the basic building block in the food web. The idea is, the little fish eat algae, and the bigger fish eat the little fish.

“There are some folks out there now that think Lake Michigan and Huron could become ecological deserts from a fishing standpoint. The food web could totally collapse because you don’t have the various organisms you need to sustain it.”

For ages, the phytoplankton fed the zooplankton, which were eaten by small, foraging fish. As the fast-filtering mussels reduce the plankton populations, there isn’t enough food to support the diet of many foraging fish. In addition, there’s not enough plankton or nutrients clouding the water to hide these small prey fish from predator fish.

Read the full article, and you'll see that introducing other sorts of fish, or relying on the appetites of the round goby, won't necessarily work the problem. At the same time, there's a Malthusian trap at work where the mussels are concerned.

Scientists say the invasive mussels may have reached their limits. With less plankton, the concentration of mussels in Lake Michigan dropped 40 percent between 2010 and 2015, according to a yet-to-be published report by Buffalo State College’s Great Lakes Center. But the total weight of mussels in the lake has risen, suggesting the surviving mussels are growing larger, said Alexander Karatayev, the center’s director. It’s unclear what this might mean in the future.

“However, it is extremely important to keep monitoring the (quagga mussel) population to understand if this decline is a long-term trend and if the population eventually will stabilize or will fluctuate substantially,” Karatayev said.

For now, better fisheries management has helped Lake Michigan see a return of lake trout.

I'll repeat a caution I issued a few years ago. "Although the researchers can quantify the various fish and mussel populations in the Lakes, they ought be careful about modulating the cycles."  Perhaps, though, closing the Seaway and further modifying the Sanitary and Ship Canal at Chicago will forestall additional arrivals with few natural enemies.