Putting Invasive Species On Trial

IRA FLATOW : This is Science Friday. I’m Ira Flatow. Japanese honeysuckle, garlic mustard, purple [INAUDIBLE], and the quagga mussel. All of those species, they are all species you might recognize as invasive to the US. That is, they were transported here from other ecosystems and managed to not only thrive in a new environment, but take it over, outcompete the plants and animals that have been there for thousands or millions of years. And invasive species are the topic of this week’s book club discussion. Dan Egan’s The Death and Life of the Great Lakes is taking our readers to ecosystems that have been completely transformed by the arrival of new species in the last century. Book club czar Christie Taylor is here with more. Take it away, Christie.

CHRISTIE TAYLOR: Book club czar. That’s where we’re at now. All right. So for people who aren’t reading along at home, chapter 6 of Dan Egan’s The Death and Life of the Great Lakes gets kind of scary. We’ve been hearing about quagga mussels, which were imported by accident from Ukraine and now carpet the bottom of Lake Michigan, and now they’re spreading outside the Great Lakes. They’re threatening to clog more waterways with their tiny, relentlessly reproducing bodies. Egan doesn’t really mince words. These mussels, like the zebra mussels before them, are the reason Lake Michigan is twice as clear as it should be, and also correspondingly poor in nutrients. Nutrients that are badly needed higher up the food chain by native fish.

Wayne State University ecologist Dr. Donna Kashian, who’s been reading the book along with us this month, says that quagga mussels are the biggest problem for her area of the lakes– the Detroit River and western Lake Erie.

DONNA KASHIAN: Quagga mussels are one of the greatest concerns to the Great Lakes and a local problem around me near the Detroit River and Lake Erie. They are a close relative of zebra mussels and have largely replaced zebra mussels in the Great Lakes. They clog water intake pipes, even nuclear power plants, displace native species, and they can have impacts all the way up the food chain to the largest fish. They’ve cost the Great Lakes over $5 million in damages.

CHRISTIE TAYLOR: $5 million. Like Donna says, the mussels are also our problem. When they get into the infrastructure of city water systems, they can quickly clog pipes and damage hydroelectric dams. Clearing them out takes time and money to the tune of millions of dollars per year. And mussels aren’t the only invasive species that have plagued the Great Lakes, just the latest. With invasive Asian carp making their way up the Mississippi from the south, it’s clear that the already challenged ecosystems of the Great Lakes may have more disruption to weather.

So, a lot of questions. What exactly does the future hold? How are scientists learning to predict which species, like those Asian carp, are actually likely to cause trouble in a new ecosystem? And with species getting transported around the globe by trade, what do ecologists have in their arsenal for deciding what’s most valuable in an ecosystem and preserving that? Where does climate change fit into all of this?

Again, a lot of questions. And we’re going to talk about it with two ecologists. My guests are Dr. David Lodge, a conservation biologist and director of Cornell’s Atkinson Center for Sustainability in Ithaca, New York. Welcome back, David.

DAVID LODGE: Thank you.

CHRISTIE TAYLOR: And Dr. Karen Alofs, Assistant Professor of Environment and Sustainability at the University of Michigan in Ann Arbor. Welcome, Karen.

KAREN ALOFS: Thank you.

CHRISTIE TAYLOR: So David, I gave kind of a definition of what an invasive species is and how it happens. But you’re the biologist. What nuance would you add to that?

DAVID LODGE: I think you hit it well. An invasive species is a species that has two characteristics. One, it came from somewhere else. It wasn’t here to begin with. And two, once it got here, it has become very abundant, and in the end, causes changes in the environment or the economy that humans don’t like. So it’s harmful.

CHRISTIE TAYLOR: And in the Great Lakes, we have this series of offenders that have changed them over time, starting with sea lampreys, is to alewives, and now these mussels, how different are the lakes’ ecosystems now from what they were before all the newcomers came into town?

DAVID LODGE: Oh, my goodness, they’re just completely transformed. We now have, if you take the Great Lakes as a whole, on the order of 200 non-indigenous or alien species. Of the animals in that bunch, about 25% are invasive. That is, harmful. They include many of the species you mentioned, others, alewives, sea lampreys, spiny water fleas, round gobys, Eurasian [INAUDIBLE], et cetera. And if we just take Lake Michigan as an example, it’s just completely transformed. If you were to go back in time to the early 19th century, you would see a completely different set of species that humans were harvesting and that, indeed, had attracted so many humans around the Great Lakes early on and continuing today, when we have 50 million people around the Great Lakes.

CHRISTIE TAYLOR: And now we have this invasive Asian carp, or potentially invasive. Why is everyone so worried about them?

DAVID LODGE: Well, we know that they’re on the doorstep, if not already in the Great Lakes. And there’s every reason to think that should they become established in the Great Lakes, particularly the lower Great Lakes, they would have very large ecological and quite likely economic impacts. So recent studies, including some work that my collaborators and I have done, suggests that if Asian carp invaded and became established in Lake Erie, they would fairly quickly, perhaps, make up a third of the weight of all the fish in the Great Lakes.

CHRISTIE TAYLOR: A third?

DAVID LODGE: And while that may sound unbelievable, it’s consistent with what has happened in places in the United States in the Mississippi River basin and the Illinois River, where these Asian carp, the same two species, have become established.

CHRISTIE TAYLOR: Karen Alofs, you’re studying inland lakes, so not the Great Lakes, but the smaller water bodies in the basin. How many Great Lakes species are getting out of those lakes and into the water that you’re studying?

KAREN ALOFS: Out of the Great Lakes themselves?

CHRISTIE TAYLOR: Yeah.

KAREN ALOFS: Yeah, so one of the examples of this type of an invasion is, we’ve already mentioned, quagga mussels and zebra mussels, those Dreissena mussels. Another is a fish called round goby, which is a small benthic fish that has invaded all of the Great Lakes. And where it has invaded, it’s become extremely abundant. And this is a small fish that can compete with many other benthic bottom-dwelling fish within the lake. And it’s also a nest predator, meaning that it’ll eat the eggs of other fishes. And this fish, the round goby, is now spreading from the lakes themselves into tributaries further upstream and then into inland lakes.

CHRISTIE TAYLOR: How is that process different from the process by which something like Lake Michigan gets invaded? Is it the same? Is it just on a smaller scale? Or can different things happen there?

KAREN ALOFS: So many of the most problematic invasive species that have been introduced to the Great Lakes themselves have been transferred by ballast water. So round goby and zebra mussels are probably examples of this, to the best of our knowledge. But in– and that ballast water is the transfer from shipping and larger cargo containers that wouldn’t be in the smaller inland lakes. The introductions of these invasive species into the inland lakes are more likely by things like the transfer of veligers, or larval mussels, that might be attached to boats, or, for example, round goby may be accidentally transferred because it’s not recognized as an invasive species and could be used as live bait.

So in the inland lakes, we have this opportunity to really change the likelihood of an invasive species being introduced, just because of the different vectors that cause their introductions. And we can change our behavior. We can clean our boats and our waders and other gear. And we can stop using live bait fish that are transferred from one body of water to another.

CHRISTIE TAYLOR: Does that mean these bodies of water are easier to protect than the Great Lakes?

KAREN ALOFS: I would say in some ways, that’s true. So the Great Lakes are different than inland lakes, and largely because of this connectivity. So veligers, or the larvae of Dreissena mussels, can spread from one habitat to another in Lake Michigan by water currents. But the inland lakes are relatively more isolated, and so it’s easier to prevent the introduction of these species, which is really our most effective means of controlling for invasions in those inland lakes.

CHRISTIE TAYLOR: What about, David, looking at once a species is here– and you mentioned that there is evidence that Asian carp are in the Great Lakes already– I mean, what happens next? Is there– what do we do to control these species once they have actually arrived?

DAVID LODGE: Well, as Professor Alofs just said, by far the very best policy and management approach is to prevent them from arriving in the first place. And we’re still hopeful, and with good reason, that the Asian carp have not established in the Great Lakes. But if they do, the challenge for management becomes very much more difficult and much more expensive.

So right now, the best approaches are to prevent still to prevent additional carp from making their way into Lake Michigan, particularly through that canal in the Chicago area that connects the Mississippi River watershed, where they are abundant, and the Great Lakes, where they are not and we hope not even established yet. And so there are a number of barriers, using a number of technologies– electrical current, bubbles, acoustic approaches– there are a variety of new things that our state and federal agencies are using to try to keep the Asian carp at bay south of Lake Michigan and prevent them from entering the Great Lakes. And that’s our best hope for the Asian carp right now.

CHRISTIE TAYLOR: Sure. I want to go back to the quagga mussels, because, as Dan writes about in his book and as we’ve all talked about offline, those quagga mussels are spreading out of the Great Lakes and going as far as Lake Mead and Lake Powell in the west, what is the solution for that now that those mussels are actually spreading? Do we give up on bodies of water?

DAVID LODGE: I don’t– there’s no scientific reason to give up on bodies of water. And I think Professor Alof’s described it well, that the way in which the Great Lakes are often the beachhead for invasions into North America. And that’s because we have so many vectors or mechanisms, like ships and boats and fishermen that are introducing species into the Great Lakes. And from the Great Lakes, they then have opened it in through the canals and recreational boaters that go across country, access to the waterways in the western United States.

But we know how to prevent those things and in areas where boat inspection stations and cleaning stations have been installed, they can be quite effective in preventing the arrival of species into a water body. Or even from an economic perspective, the best way is to prevent species from leaving the already infected lakes, in this case, the Great Lakes. So we know that quagga mussels and zebra mussels made their way across the continent to Lake Mead and then other western waterways by clinging to recreational boaters that left the Great Lakes in the winter to go someplace warmer in the American Southwest in the summer. We know how to prevent those things. We just have underinvested in actually implementing the management steps that are needed.

CHRISTIE TAYLOR: Thank you for that response. Just breaking in here to remind people that I’m Christie Taylor and this is Science Friday from WNYC Studios. Talking about invasive species in the Great Lakes and beyond. And Dr. Alofs, I wanted to talk more about what makes a species capable of invading. You know, that we talked about there are something like 200 non-native species in the Great Lakes themselves. But a lot of them haven’t actually risen to the level of quagga mussels, zebra mussels, gobis. What are the traits that an animal or a plant needs to completely take over a new ecosystem?

KAREN ALOFS: This is a really good question. So I think our conversation has already hit on a couple of important points. So if we have to think about the potential vectors for any species, so how it might be taken from one water body to another, for example, and how frequently that transfer may happen, so the [INAUDIBLE] pressure of those different vectors. We also have to think about the habitat and prey suitability of the areas that they’re being introduced to. So for example, one of the reasons that we’re so concerned about Asian carp being introduced to the Great Lakes is that it has a really wide thermal tolerance. So if the lakes were too cold for Asian carp, it would be much less of a concern. But they’re definitely not too cold or too warm.

And then finally, we think about things that we call life history traits. So for example, how quickly a species will reach its reproductive maturity and start to produce offspring. And how many offspring it will produce at a time. And all of these different factors can be really predictive of whether an invasive species is going to establish and whether it’s going to continue to spread and become more abundant and have impacts on the ecosystems from there.

CHRISTIE TAYLOR: And you mentioned water temperature. And this is a question I have for you, but also for David a little bit, but the climate is changing. And one thing that happens when the climate changes is we’re seeing species move to different parts of the world that they haven’t been in voluntarily because of changing temperature zones. What does that do for our definition of what species are native and what species are invaders? Dr. Alofs?

KAREN ALOFS: Right. So they’re– as climate is warming, we have the expectation that species will move their distributions, both to higher latitudes and higher altitudes to track their thermally preferred habitats. And this is already happening. We’ve seen these changes in species distributions or range expanders occurring across the globe and through different species of animals and plants.

For example, I’ve been working on range expansions in inland lakes across Ontario. So this is the northern rangelands limit of many warm water species falls across Ontario. For example, small mouth bass and large mouth bass are warm water adapted predators, so using natural resource data and monitoring data, I’ve been able to show that these are two of the species that are expanding their ranges northward. And they’re establishing in inland lakes that were previously too cold for them. So these species are sometimes referred to as native invaders, or more simply as range expanders.

CHRISTIE TAYLOR: Range expanders. So that’s– is that the– I mean, David, if we’re looking at a future of change, what is your outlook on invasive species, protecting ecosystems, and deciding what we need to protect? As we wrap up.

DAVID LODGE: Well, I think that the best case future that we might desire is really up to society to define. Those of us who are scientists can describe what has been, what is, and what could be. But the choices really have to be societies. I think– my experience, most people in the Great Lakes basin would agree that they want high water quality. They want high quality recreational opportunities. And high quality valuable fishing opportunities. And many people value native species. So as the environment changes, and as we have more innovative ways to both predict and manage, even in the face of climate change, we can do much more to prevent harmful species arriving and to benefit species that we like.

CHRISTIE TAYLOR: And we’re going to have to leave it there, unfortunately. I’m really sorry. Thank you to both my guests this hour– David Lodge, Professor of Ecology and Evolutionary Biology at Cornell’s Atkinson Center for Sustainability, and Dr. Karen Alofs, Assistant Professor in the School for the Environment and Sustainability at the University of Michigan in Lansing. Thank you for joining me today.

IRA FLATOW : Thank you, Christie. It’s not too late to pick up Dan Egan’s The Death and Life of the Great Lakes and get your book club on. And for our New York listeners, we have an event with author Dan Egan coming up on February 20th. Go to ScienceFriday.com/bookclub to get tickets and find our newsletter, discussion questions, and more.

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