The Great Lakes’ Mussel Invasion

The tiny quagga mussel may only be the size of a fingernail, but it’s taking over the Great Lakes and immobilizing a $7 billion-per-year commercial and recreational fishing industry. Over the last 15 years, mussel populations have soared, and Tom Napela, a research biologist with the Great Lakes Environmental Research Lab at the National Oceanic and Atmospheric Administration (NOAA), estimates there are now 437 trillion mussels in Lake Michigan alone.

“They find the conditions very suitable and just explode in terms of population numbers,” Napela said. “And during the period of exponential growth, they wreak havoc on other organisms. They take away resources and out-compete native species.” For the past 20 years, Nalepa has been evaluating population trends and the impact of the mussel invasion on the Great Lakes, which has caused $5 billion in economic losses to the region over the last decade, according to the U.S. Fish and Wildlife Service.

The mussels are so destructive because they wipe out critical food at the bottom of the food chain, including organisms like plankton, the main food source for a shrimp-like organism known as Diporeia. “It’s a very important fish food organism,” Napela noted. “Hence, this has led to declines in the growth and condition of fish populations that once depended upon Diporeia as a food source. So it’s led to a cascading effect from one species to the other throughout the food web.”

The mussels also clog water intake pipes, sometimes cutting off drinking water supplies and requiring expensive remediation. “They load up so much,” said Kirk Kleist, Operations Manager at the DuSable Harbor in Chicago. As a diver for over 30 years, Kleist has also noticed dramatic changes in the lake’s clarity from mussel filtering. “Thirty years ago, you had five feet of visibility at the max. Now I have seen 40 to 60 feet of visibility.” Ironically, the clearer water is a bad thing.

“Water clarity has increased two- or three-fold, just because of the ability of mussels to filter all the particles out of the water, which they use as food,” Napela continued. “So, if you like clear water, certainly, when you look out at Lake Michigan, you have it. But clear water also means that there’s no food in the water for all the other organisms.”

Another side effect of excess clarity caused by the quagga’s filtering is that it encourages abnormal and toxic algae blooms. “[The mussels] allow, for the first time in the life of the Great Lakes, sunlight to pierce all the way down to the bottom,” said Henry Henderson, director of the Natural Resources Defense Council (NRDC)’s Midwest Program. “And that creates the ability for toxic algae to grow, which is poisonous and a threat to our public health and safety.” A report published by the National Wildlife Federation (NWF) in October called the toxic algae blooms that infested Lake Erie this year the most harmful ever recorded.

“When the Cladophora washes up on beaches, they often harbor problematic bacteria, including botulism, which then can negatively impact fish and birds that consume somewhere in the food web,” said Michael Murray, a staff scientist with the NWF’s Great Lakes office in Ann Arbor, Michigan, and co-author of the report. Consequently, commercial fisherman Dennis Hickey and his crew are spending valuable time and money pulling algae out from their nets.

“Well, it gets worse every year. The last five years, I say, it’s been increasing,” he said.

And business revival for Hickey and others doesn’t look promising, as scientists theorize that removing the mussels from the lake would be impossible without chemically eradicating everything else in the water first.

“Quagga mussels are going to be with us now forever, I think,” Napela reckons. “It’s just a matter of at what abundance does the population stabilize? And that’s the key.”