By Leslie Mertz
An entire group of native organisms is dying off in the lakes and rivers of the Great Lakes region, and children are noticing.
They are native freshwater mussels, those interesting and long-lived “clams” that lie partly buried in the water bottom.
“It’s kind of sad. They’re part of the lake, part of my life,” said 15-year old Tabitha Sutterfield of Dansville, Mich. As a little girl, she spent many an hour on family vacations following the mussels’ meandering trails through the sand in Houghton Lake, Michigan’s largest inland lake, and then scooping up the native mussels.
“They had an odd shape to them and they were really pretty-looking,” she said. “It was weird thinking that they were alive, and they didn’t have eyes or a mouth.”
Today, native mussels are nearly gone from that lake, and from many other lakes and rivers throughout the region. They are victims of the army of zebra and quagga mussels that have infested waterways throughout the Great Lakes region. Native to eastern Europe, these often fingernail-sized intruders attach to hard surfaces, including native mussels, and do so in such numbers that they can prevent the native mussels from opening. If they can’t open, they can’t feed, breathe or breed.
“When I was younger, they were pretty easy to find,” Sutterfield said. That changed about seven or eight years ago, when she noticed scores of empty native mussel shells washing up onto shore. At the same time she began wearing water shoes to keep from cutting her feet on the sharp-edged zebra mussels that were accumulating on native-mussel shells, and on driftwood, pebbles, and even on each other.
The shallow water and other characteristics that make Houghton Lake such a good habitat for native mussels unfortunately also make it well-suited to zebra mussels, said mussel researcher David Zanatta, assistant professor at Central Michigan University’s Institute for Great Lakes Research. “In addition, Houghton Lake drains into the Muskegon River, and the Muskegon is filled with zebra mussels, too.”
Native mussels are indeed nearly gone from the Muskegon, said Peter Badra, aquatic biologist with the Michigan Natural Features Inventory, a program to locate, identify and document threatened and endangered species and communities throughout Michigan.
Other waterways, such as the Au Sable, Manistee and Detroit rivers, are similarly seeing huge declines.
“The Detroit River used to be one of the best, most diverse systems in Michigan for native mussels in terms of number of species,” he said. “We don’t see any live native mussels in the Detroit River anymore. We haven’t seen any in our surveys.”
Likewise, native-mussel populations in Lake Erie, Lake St. Clair and Lake Ontario are far less dense today than they were just a couple of decades ago, Zanatta said. “Lake Erie probably had on the range of at least two native mussels per square meter of the lake bottom before zebra mussels came in. Compare that to now, there’s (almost) none.”
In Zanatta’s surveys of coastal areas of the three lakes – the only areas where native mussels remain – the density of native mussels is 0.01 per square meter. “When something is decimated, it’s reduced by a factor of 10. This is decimated, and then decimated again,” he said. “It’s really bad.”
Despite the drastic declines in so many waterways, all is not lost. Pockets of native mussels persist here and there, especially in rivers, Badra said, and some rivers remain mostly zebra-free. That’s due in large part to the different life cycles of the mussels. Zebra mussels release their microscopic larvae into the water, and the larvae float on currents until they make contact with a hard surface where they can attach. Native mussel larvae instead temporarily latch onto the gills of fish until they drop off and start their lives on the lake bottom.
“That means the native mussels get transported upstream when they’re attached to their fish host,” he said, so they can spread throughout a river. Conversely, he said, “The zebra mussels have a hard time persisting in flowing-water environments, because they always get washed downstream.”
Zebras have, however, spread in many rivers. “The problem is that we put in our boats in different lakes and impoundments, so we inadvertently keep transporting the zebra mussels to different spots upstream,” Badra said. “The Muskegon, Manistee and Au Sable get a lot of boat traffic, and there are really a lot of zebra mussels there because they are constantly transported upstream and reestablished.”
Boat traffic is also a major issue in the lakes, Zanatta said. “The Great Lakes are completely infested with zebra and quagga mussels, so if you boat in the Great Lakes and then go to an inland lake (without thoroughly cleaning the boat), you are transporting them.” Still, he said, some remote lakes remain free of zebra mussels and have thriving native-mussel populations, and others still cling to small, remnant native mussel populations despite the zebra invasion. “The fact that they are still surviving is promising,” he said.
Back at Houghton Lake, Tabitha Sutterfield plans to continue scraping zebra mussels from every live native mussel she finds within 50 feet of the dock. She, her grandfather and her aunt have been doing that for several years now, and have seen a difference. While they cannot find a single living native mussel just a short walk to the east or west in the lake, they can quickly spot three to four dozen living native mussels still making their trails in the sand around the dock.
“I feel really of proud of myself,” she said. After all, she added, “I’ve known them since forever. They’ve always been in the lake.”