National Lakeshores Threatened by Non-native Species
Loons, mergansers, cormorants and other waterfowl are dying by the thousands in the Great Lakes due to an invasion of non-native species that are threatening to turn the lakes' ecosystem upside down. At Sleeping Bear Dunes National Lakeshore even piping plovers, a threatened species, are dying.
Exotic, or non-native, species in the Great Lakes are nothing new. Dubbed "biological pollutants" by some, in the Great Lakes these species include alewives, white perch, and sea lampreys. Not only can they have devastating impacts on the native fisheries, but the costs to try and control them are staggering.
One of the latest threats posed by exotics is taking aim on not just Lake Michigan's fisheries, but also its waterfowl and shorebirds.
“We’re basically seeing, to be honest with you, an ecological change, or an ecosystem change, of the Great Lakes," says Ken Hyde, the wildlife biologist for Sleeping Bear Dunes National Lakeshore. "We’re right smack dab in the middle of it. (In) 2006 we had over 2,900 waterbirds, including loons, gulls, cormorants, grebes, mergansers, had that many die and wash up just on our beaches."
Cause of death? Botulism. Specifically, Type E botulism (see attached pdf), which is native to the Great Lakes and which Ranger Hyde says will show up from time to time and then vanish.
Now, though, that cycle is changing, largely because of two or three non-native species.
One is the Round Goby, a fish native to the Black and Caspian seas that showed up in the Great Lakes in the mid-1990s, most likely hitchhiking there in the ballast water of an ocean-going ship.
The other is the Quagga mussel, another hithchiker that is indigenous to Ukraine and which was first spotted in the Great Lakes region back in 1989.
A third non-native that might also be contributing to the problem is the Zebra mussel, a shellfish smaller than the Quagga mussel and which hails from Russia.
"We, of course, have Zebra mussels, and now we have Quagga mussels, who are the big ugly cousins of Zebra mussels," says Ranger Hyde. "They can go out deeper in the lake. They’ve done a huge expansion in Lake Michigan the last few years. They can also attach to sand, where the Zebra mussels were really limited to hard surfaces, cobble, pipes, that type of thing."
The problem with these shellfish is that they act as millions of tiny filters in the lakes.
“In the process of them getting established, they’ve cleaned up Lake Michigan. They’ve filtered all the water out, so the amount of sunlight getting to the bottom has increased exponentially, and so we have a whole lot more native algae growing," says the wildlife biologist. "The main one is Cladophora, which is kind of a filamentous algae."
So prolific has this algae become under the clearer water conditions that it actually shows up on Google Earth, according to Ranger Hyde, who has used that satellite tool to predict where there will be new outbreaks of botulism.
Here's how these pieces come together to create a biological bomb: The two mussel species filter the water, enhancing the growing conditions of the algae. As the algae continues to grow, and as the mussels continue to multiply, dead, dying and rotting algae and mussels create the perfect environment for Type E botulism to flourish.
The Round Gobies feed on this decaying algae, as well as the dying mussels, and ingest the botulism. Then the waterfowl -- the loons, cormorants, mergansers and other fish-eating birds -- feast on the dying gobies, ingest the botulism, and die.
"It looks like this Type E botulism is using either the decaying mussels on the lake bottom or the decaying algae as a growth medium. Something stirs it up or it gets fed through whatever -- the Quagga mussels, the Zebra mussels and also all of your macro-invertebrates pull in that toxin from the botulism -- and then those get eaten on by the Round Gobies," Ranger Hyde explains.
"And with the huge population of the gobies, all of a sudden you have a bunch of little sick fish floating at the surface, which is a buffet for a fish-eating bird," he adds.
This past year the lakeshore saw practically a doubling in the number of bird species felled by this ecological onslaught. Shorebirds are falling victim as they feed on mussel shells and algae that washes ashore, as well as on the insects that feed on the dead waterfowl.
"We lost four piping plovers ... and also several Sanderlings, a few killdeer, and then just a few odds and ends," says Ranger Hyde. "I think we ended up with seven or eight different species of fish, from carp and sturgeon, which both vacuum there along the lake bottom, to drum and perch and a few others that will actually eat mussels."
Against these die-offs is an undercurrent of ecological transformation in the lakes, he says.
“What they consider the main food item at the bottom of the food chain was a little shrimp called a Diporeia shrimp, and at the 'State of Lake Michigan' they put up some slides showing that those shrimp lake-wide are down 90 percent," the ranger said. "And then in the next few presentations they showed that the Cladophora has increased exponentially (and) Round Gobies and the mussels of course have spread throughout most of the Great Lakes.
"And so we’ve lost that primary food source, the small shrimp, but you’ve also lost much of the Zooplankton and other things that were even smaller than it, because the mussels can filter it out of the water also," says Ranger Hyde. "And now we’ve got what we call a 'fishhook flea,' we’ve got a little shrimp called a 'red shrimp.'"
As these exotics have grown in number, they've replaced much of the native sculpin and other small bait fish in the lakes, he says.
So far, according to the wildlife biologist, Sleeping Bear Dunes seems to be the hardest hit of the lakeshores by these exotics.
“Most of your parks or lakeshores (Isle Royale National Park, Apostle Islands National Lakeshore, Pictured Rocks National Lakeshore) that are up on Superior aren’t having a lot of this yet because Superior is so much colder and deeper," says Ranger Hyde. "You don’t hear a lot of this except for us right now.”
While Indiana Dunes National Lakeshore at the southern tip of Lake Michigan has reported Quagga mussels, the ranger didn't know if Round Gobies were also a problem there.
Trying to devise a strategy to attack the problem has not been easy, largely because of the scale involved.
“When it’s showing up on Google Earth," says Ranger Hyde, "it’s hard to say that’s a small problem.”
|Cornell Botulism info.pdf||699.4 KB|