Beaches along Lake Michigan are closed when E. coli bacteria gets too high. But a nasty critter found on the bottom of the lake might help keep the beaches open.
E. coli gets into the water and on beaches through stormwater runoff and sewer overflows. But those are a relatively small part of the problem. Most of the fecal bacteria comes directly from visitors.
“It can be deposited directly from skin shedding from people on the beach. It can also be deposited by wildlife defecation, and diapers, and restrooms that are poorly maintained,” said Chelsea Weiskerger.
She’s a PhD student at Michigan State University. She and her research partner Richard Whitman looked at E. coli records from 15 years of sampling at 64 beaches along Lake Michigan and western Lake Erie shorelines.
“We actually found a somewhat surprising trend. We found that E. coli have actually been decreasing along the Lake Michigan shoreline between 2000 and 2015,” Weiskerger said.
The people who manage the beaches would like to think it’s because of better management. But there are just as many seagulls and people visiting the beaches, so that’s not likely the answer.
Weiskerger and Whitman think the trend might be due to quagga mussels. Those are invasive mussels that made their way from Eastern Europe, likely in the ballasts of cargo ships. They’re cousins to zebra mussels, except that quaggas blanket the bottom of much of the Great Lakes.
“The mussel density in Lake Michigan was estimated to be nearly 10,000 mussels per square meter. So, they’re basically carpeting the bottom of the lake. That’s where their sort of power comes, is that they just have so many mussels in such high densities in the lakes that they can have these impacts,” Weiskerger explained
There are estimates ranging from tens of trillions to hundreds of trillions of invasive mussels.
“We think that these mussels are having a big impact on the lake and that includes the E. coli. We think that they’re filtering the E. coli out of the lake directly and just kind of acting as predators on the E. coli,” she said.
In addition to filtering out E. coli, the quagga mussels filter out much of the particulate matter suspended in the water. The water is clearer. That means the sun’s ultraviolet rays reach farther below the surface of the water.
“And those UV rays, they can come in and they can damage the DNA of things like E. coli and other bacteria. When that does that, it renders these things either temporarily or permanently inviolable, like inactivated," Weiskerger said.
So, fewer beach closings along Lake Michigan’s shoreline. Yay, quagga mussels! Right?
Well, no. Drew YoungeDyke at the National Wildlife Federation’s Great Lakes Regional Center says quagga mussels have done far more bad than good.
“Well, they’re bad for the same reason that zebra mussels are. They affect the Great Lakes in a similar way,” YoungeDyke said.
Similar in that they clog up water pipes, attach to boats, rafts, damage native mussels by so many of the quaggas attaching to the Great Lakes' natives' shells that they’re more or less smothered.
YoungeDyke says that’s not the worst of it.
“They filter out the base level of the food chain. So, it starves out the zooplankton and phytoplankton. Well, that’s what the base level fish eat, that’s what our predator fish eat, that’s what our game fish eat," YoungeDyke explained.
Those trillions of quagga mussels are sucking the life out of the Great Lakes.
The MSU researchers Weiskerger and Whitman also note that the decrease of E. coli bacteria just might mean something else. If other bacteria are decreasing, it could have serious implications about the health of the lake. Bacteria are responsible for recycling the carbon and nutrients which kick start the base of the food web. If all bacteria are disappearing because of quagga mussels, the whole of the ecosystem could be at risk of collapse.