Our April pick for the PBS NewsHour-New York Times book club, “Now Read This” is Dan Egan’s “The Death and Life of the Great Lakes,” an epic portrait of the Great Lakes and the perils they face. Become a member of the book club by joining our Facebook group, or by signing up to our newsletter. Learn more about the book club here.
When we think of invasive species threatening the Great Lakes, most of us think of the ugly face of the Asian carp. But in “The Death and Life of the Great Lakes,” journalist Dan Egan tells us there are other invasive species posing immediate dangers, including the quagga mussel, which is sucking Lake Michigan dry.
Below, Egan annotates a page of his book on the devastation wreaked by the quagga mussel. In his annotations, Egan describes the challenge of conveying how damaging a tiny and seemingly harmless species can be, how many detours he took in the book’s research process, and how some of the learnings of the book came from a simple trip with his daughters to the beach. Read more below:
From page 123-124
The public can comprehend the devastation of a castrophic wild fire that torches vast stands of trees, leaves a scorched forest floor littered with wildlife carcasses and turns dancing streams into oozes of mud and ash. But forests grow back. The quagga mussel destruction is so profound it is hard to fathom.
“People look at the lake and don’t think of it as having a geography. It’s just a flat surface from above—and from there it looks pretty much the same as it did 30 years ago, but under water, everything has changed,” University of Wisconsin–Milwaukee ecologist Harvey Bootsma says.
The mollusks now stretch across Lake Michigan almost from shore to shore.
People might still think of Lake Michigan as an inland sea full of fish. It’s more accurate to think of it as an exotic mussel bed sprawling across thousands of square miles. Lake Michigan’s quagga mass in one recent year was estimated to be about seven times greater than the schools of prey fish that sustain the lake’s salmon and trout . Under some conditions the plankton-feasting mussels can now “filter” all of Lake Michigan in less than two weeks, sucking up the life that is the base of the food web and making its waters some of the clearest freshwater in the world.
Just how much have things changed since quagga mussels took over? A simple way to gauge the amount of plankton in a water body is to take a visual sounding using a crude device called a Secchi disk, named after a 19th-century Italian priest tapped by the one-time Papal Navy to take water clarity readings in the Mediterranean.
The disk is, typically, an eight-inch diameter metal plate with four equally sized alternating black and white wedges, almost like a monochromatic version of the yellow and black nuclear fallout shelter sign. It is lowered by rope into a water body and the point at which it disappears is the water’s Secchi depth.
In the late 1980s, before the mussels blanketed the lake bottom, Lake Michigan’s average Secchi depth was 6 meters, or about 20 feet. By 2010 the average depth had tripled and readings began coming in at beyond 100 feet. This nearly vodka-clear water is not the sign of a healthy lake; it’s the sign of one in which the bottom of the food web is collapsing.
One study on southeastern Lake Michigan revealed that by 2009, phytoplankton levels in springtime—the prime plankton-growing time of year—had dropped nearly 90 percent since the mussels took over the lake bottom. It’s probably not a coincidence that the lake’s fish populations have dropped at the same time.
Annual trawling surveys show the lake’s biomass, or overall weight of prey fish, has plummeted from an estimate of about 350 kilotons in the late 1980s to barely 5 kilotons by 2014. And then a federal fisheries survey crew went fishing one warm September day in 2015.