I still remember having an experience with zebra mussels at a very young age. Every summer since I can remember, my family and I have spent many weekends on the shores of Lake Erie cruising around in our fishing boat trying to pull in walleye and perch. Every now and then, however, you catch something not worth keeping. Catfish and sheep head immediately come to mind.
(Recipe for sheep head: Cook fish on cedar plant over 350 degree grill for an hour and then eat the plank.)
But then one summer, I began reeling in something completely different – a giant clump of tiny, fingernail-sized black shells somehow clinging to my night crawler, hook and line. Little did I know how much of an impact the presence of these zebra mussels would have.
Zebra mussels and their close relatives quagga mussels are invasive species, meaning they are not native to the Great Lakes. Through shipping boats and a global economy, they were introduced to the ecosystem within the past couple of decades. To say they’ve thrived is an understatement. Sure, one tiny mussel filters only about a quart of water per day. But when there are billions of them blanketing the bottom of a lake, they’re going to have an impact.
That impact is the focus of a new study from the University of Michigan’s Mary Anne Evans. In short, the mussels are eating the entire base of the food chain, giving little hope of survival for other species that rely on the food source.
The food source I’m talking about is algae, including single-celled plants called diatoms that are encased in glass-like shells made of silica, which the diatoms extract from the water. In a healthy ecosystem, these algae build their shells every year, soaking up the silicon from the upper layers of the lakes and sink to the bottom. The amount of silica that disappears every year is used as an indicator of the ecosystem’s health because the algae is important for the survival of other species.
Of particular concern is Diporeia, a tiny shrimplike creature that was one of the pillars supporting the base of the Great Lakes food web. Nearly every fish species in the Great Lakes relies on Diporeia at some point in its life cycle. But because the levels of diatoms are 80% lower today than 20 years ago, Diporiea populations have crashed in lakes Michigan and Huron. That change is already impacting Great Lakes commercial fisheries and the sport-fishing enterprise.
Nobody is sure what will happen next. Perhaps the mussels will overeat their own food supply and shrink back in population. Or maybe it will just get bigger and stay there, continuing to decimate the Great Lakes’ ecosystem.
I sure would be said if lake perch became a delicacy due to their disappearance.