Nature is full of heartwarming stories about partnerships. One of my all-time favorites is the three-way mutualism between Western ponderosa pine trees, tassel-eared squirrels and mycorrhizal fungi. The trees house the squirrels in their branches and the fungi on their roots. The mycorrhizae break down nutrients in the soil for easier absorption by the tree roots, and the trees supply sugar to the fungi. The squirrels eat the fruiting bodies of the fungi, called truffles, then defecate the spores throughout the forest, thereby inoculating new trees. Everybody benefits; forest health improves.
Pan east about a thousand miles to the Great Lakes region. Lurking beneath Lake Michigan is another partnership that’s just as impressive. But its effects on the Lake Michigan ecosystem are anything but beneficial, at least the way we perceive a healthy freshwater scene.
Earlier today, about 30 of us attending the Society of Environmental Journalists conference toured the University of Wisconsin’s Great Lakes Water Institute in Milwaukee. We also cruised the lake for a couple of hours aboard the EPA’s research vessel, called the Lake Guardian. Of all the research, I was most struck by new insights into the efficient relationship between quagga mussels and an algae called cladophora.
Ten years ago, scientists were sounding alarms about zebra mussels, Russian stowaways that hitched rides to the Great Lakes aboard ocean liners in the late 1980s and quickly expanded to cover the lake bed close to shore. The inch-long invaders proved annoying and costly, covering anchors, buoys and submerged ladders, and cutting bathers’ feet with their sharp shells.
But already, the zebra mussels have been crowded out by their even more prolific cousins: quagga mussels. Hardier and more adaptable, quagga mussels can live in colder, deeper parts of lakes where zebra mussels can’t. Each quagga mussel filters 1.5 quarts of water a day, extracting nutrients like phosphorous that would otherwise be available for native species, and concentrating it at the lake floor. That means visibility above the mussels is much improved — but the entire food chain is on the decline.
What’s even more amazing is that the quagga mussels transform the lake into a nursery for another invader: cladophora. The long, filamentous algae can take advantage of the rich phosphorous around the mussels, and it likes the extra sunlight that filters through the newly cleared water. The algae turns rocks into gardens wherever it takes hold. But in rough water, cladophora breaks off and floats free, covering beaches with stinking bacterial breeding grounds and costing power companies millions of dollars in clogged pipes.
Now, would-be lake stewards find themselves in a bind. Markets for quagga mussels aren’t obvious. They’re terrible eating, and burning them as biomass would require destructive dredging of the already beleaguered lake floor. Harvey Bootsma, a UW-Milwaukee scientist, said in smaller water bodies, chemicals could be added to kill the mussels — but “there’s virtually nothing you can do in a body of water as large as Lake Michigan.”
Even reducing the amount of available phosphorous in the lake with tighter pollution controls, which might seem like a no-brainer, carries unsavory risks — especially for the open-water fisheries that are already suffering the reduction in available nutrients.
I can’t help trying to take a step back on this one, avoiding a view of it as a “bad” environmental story. I’m impressed with the rapidity of the changes — with the sheer natural action of the story. Wherever quagga mussels and cladophora take the lake from here, this eco-drama will be one to watch.
This post also appears on the SEJ blog, at http://sej2009.sej.org/.