Great Lakes Freezing: Botulism in Lake Michigan off Sleeping Bear Dunes

Since 2010, the United States Geological Survey and the National Park Service have cooperated on a study aimed at diagnosing the spread of botulism within Great Lakes ecosystems.  While not a substantial threat to humans—across species, different botulism toxins are poisonous to varying degrees—botulism in the Great Lakes has led to the deaths of innumerable fish and birds.  The spread of invasive species, seasonal temperature and water level shifts in Lake Michigan, and subtle chemical imbalances have all led to the devastating effects of widespread botulism poisoning. MyNorth’s Evan Perry conducted the following interview with Stephen Riley—a lead researcher with the US Geological Survey who is working on the current study—to get the inside scoop on the current state of botulism in the Great Lakes and the way it may or may not be affected by the freezing (or near freezing) of the Great Lakes this winter.

The bacteria that cause botulism are common—sort of like a bread mold—so when does it create the toxin that leads to botulism in birds and fish?

First, there has to be an anaerobic environment—no oxygen.  The bacterial spores are everywhere, but the bacteria only grow under certain conditions—certain temperature ranges, a certain pH, but, most importantly, no oxygen.  We think, but we aren’t 100% sure, that there’s all this algae called Cladophora piling up on the lake bottom and starting to rot, which creates anaerobic conditions that the bacteria can grow in. Because of the unique characteristics of the Sleeping Bear area, where there are all these deep holes where the algae can settle, we think that a lot of botulism toxin is being produced there.

Botulism outbreaks usually don’t happen until the fall.  Storms will dislocate a bunch of algae, and that will settle underwater and allow the bacteria to take root in the algae.  Then another storm will come and stir up the mix, which bugs will feed on, beginning the spread of botulism up the food chain.

Will the lakes freezing over this year affect the risk of botulism?

I don’t think that will affect botulism that much.  We published a paper a few years ago that showed that the lower the lake levels and the higher the temperature in a given year, the more likely a botulism outbreak will occur.  Ice cover will likely raise the lake levels a little bit, as there won’t be as much water evaporating off of the lakes.  So it might be a better year because the lake levels will go up.

The water temperatures in the spring appear to be critical to the spread of botulism; we’re not sure why, but our data show that the higher the water temperature from April to June, the higher the bird mortality rate.  So if the lakes stay cold through the spring, and if the lake levels rise up a bit, then it might be a good year.

Is the risk of botulism growing with the spread of invasive species in the Great Lakes?

We think so.  First of all, the reason we have more algae is the quagga mussels—which are similar to zebra mussels, but can colonize bare sand and live at greater depths than zebra mussels.  The mussels clarify the water—they take everything out—and water clarity has increased over the last decade or two to the point that you can see down to the bottom at a depth of 50 feet.  So that increases the area where the algae can grow, because light can now reach lower depths.

Mussels also provide a substrate for algae. Cladophora can’t grow on bare sand, but when you have mussels that colonize on the sand, then the algae can grow on them.  So that’s two ways that the amount of area that can be colonized by algae has increased.  The third thing they do is feed the algae phosphorous.  The mussels will take particulate phosphorous out of the water, and excrete it as soluble phosphorous, which the algae can take up directly.  So basically you’ve got these big beds of mussels that act as substrates for the algae to grow on, and they provide it with phosphorous.

There used to be a bad algae problem in the Great Lakes in the 60′s and 70′s, when there was a lot more phosphorous in the lakes because of agricultural run-off.  We’ve cleaned up the phosphorous in the last few decades, but now the mussels provide a direct subsidy of phosphorous to the algae.  So there’s actually less phosphorous in the water column if the lakes overall, but phosphorous levels can be pretty high where the mussels are, and the algae can take it up right there.

What are the goals of your current research, and how is that research being conducted?

We’re first trying to figure out where it’s being produced.  We’re going around and sampling sediment, and we use a technique called Polymerase Chain Reaction—PCR for short—to pinpoint the gene that produces the toxin.  So we’re taking samples all over the Sleeping Bear area at different depths and in different places, to find out where the toxin is being produced.

The second step is to figure out what animals in the lake are carrying the toxin.  Something has to be picking it up—some bug is rooting around in these piles of dead algae and picking up the toxin in its diet.  Then a fish will come along and eat that bug, and get the toxin in its system.  Then a bird will come along and eat that fish.  So we’re trying to figure out the exact organisms involved—what bugs and fish are moving the toxin up the food chain.

The ultimate goal is to figure out a way to stop it.  If we found out, for example, that this was occurring at a certain range of depth, then maybe we could go down and dig that algae out—but that might be dangerous because it could spread the toxin.  We don’t know if that’s even a feasible way to do it.  Another way would be to scare the birds away from the area where the toxins are being produced with some sort of noise-making device.  The problem is loons: loons dive when they’re scared—they don’t fly away.  So you might be scaring a loon right down to the area that we want them to avoid.  We don’t really know how feasible these things are, but once we find the mechanism and the locations of where this is happening, we may be able to figure out some way to chase the birds away, or even stop the toxin from being produced.

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