Did Algae Contribute To Mass Extinctions?

Forget asteroids — a new theory says algae were the key to the dinosaurs' extinction millions of years ago. Ecotoxicologist John Rodgers details the evidence for the theory and explains why some algae can be harmful in large quantities, even to present day animal populations.

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JOE PALCA, host:

Up next, a new theory about how the dinosaurs became extinct. Forget volcanoes, asteroids, rising sea levels. The real reason is killer algae, or at least that's according to a new theory by two Clemson University researchers.

Joining me now to talk about this idea is one of those Clemson scientists. John Rodgers is professor of forestry and natural resources, and the director of the ecotoxicology program at Clemson University in South Carolina.

Welcome to SCIENCE FRIDAY.

Dr. JOHN RODGERS (Professor of Forestry and Natural Resources, Clemson University; Director, Ecotoxicology Program): Good afternoon.

PALCA: So what brought you to this theory of algae as being, you know - because we know that there are certain toxic algae, I'm - I grant you. But algae that are toxic enough to cause mass extinctions?

Dr. RODGERS: Well, as an ecotoxicologist, part of my life is spent studying algae and algal blooms and so-called harmful algal blooms. And in partnership with my colleague, Jim Castle, who's a geologist, one day we started talking about the notion that many of the algal blooms that we were seeing were becoming more widespread. The toxins were becoming more intense. Their potency was becoming more intense. Their production was very high so they were consuming lots of oxygen. And he said, well, this is - this certainly has application in terms of mass extinction.

So we started scouting out the literature and found out that other scientists had offered the notion that certainly algae could cause local mass extinctions. And then we expanded from there to looking globally and said, there are quite a few mass extinctions that have happened in the past that we can relate to algal production as well as the examples from the current research that we're doing. So there were examples from the past as well as current examples ongoing. And that sort of led to the development of that hypothesis.

PALCA: Interesting. And I want to invite our listeners to ask questions about this as well. The number is 800-989-8255.

So, now, I'm wondering how would you go about proving this or substantiating it?

Dr. RODGERS: Well, as all scientists would, we would certainly set about to test this hypothesis. And our initial test involved looking at the rock record at the major mass extinctions from the past. In the past, there have been five major mass extinctions that have been recognized by paleontologists and geologists and so on. And so, we initially carefully looked at those mass extinctions and started asking questions about, did this correlate or did these mass extinctions correlate with the presence of fossil algae? Or was there evidence of algal blooms and algal toxicity in the rock record? And as we looked hard at that, sure enough, there was.

PALCA: So you're actually seeing at the same time that the number of different species are going down, the sheer numbers of algae are going up?

Dr. RODGERS: Yes. And there are actually several ways that these algae can get you. The two, probably, most important ones are the production of toxins that we talk about a lot. And then, the other way is the anoxia that many geologists and geoscientists have noted. They have noted that in the formation of certain shales and so on, certain algal shale - that there was apparent anoxia. And that's one of the things that algae are good at.

PALCA: Anoxia, maybe you can explain that.

Dr. RODGERS: Well, when these algae die, as they produce these massive blooms that are - they have a lot of organic carbon. They're very readily biodegradable. As these algae die, they consume quite a bit of oxygen. And actually, they can consume enough oxygen so the waters simply go anoxic, sort of like the anoxic area out in the Gulf of Mexico off of the mouth of the Mississippi River.

PALCA: Right. These - what we sometimes call dead zones?

Dr. RODGERS: Exactly.

PALCA: I see. So, you're suggesting that there's two mechanism. What kind of toxins - I mean, would you just say that the - they don't - there weren't more toxic algae there just were a lot more of them, and together, they were, you know, largely toxcious(ph) just by their numbers?

Dr. RODGERS: Well, certainly, that - both of those are possibilities. In other words, that the toxins they were producing were potent, and changed their potency because we see that currently, that algae have a capability of producing or changing the potency of their toxins. Sometimes, they have the ability to turn on or turn off production of toxins as a result of environmental cues. And then, these toxins that we see are things like neurotoxins, as well as other liver toxins, hepatotoxins and so on. And so, we see a variety of toxins ranging all the way from cyclic peptides to alkaloids. So, we see a whole variety of toxins produced currently, and now, it's time to go to the rock record and see what we can find in terms of residuals of those.

PALCA: We're talking with John Rodgers of Clemson University about a new theory he's published this week in PNAS journal about algae possibly being a cause of mass extinctions. I'm Joe Palca, and this is SCIENCE FRIDAY from NPR News.

So, in the introduction, I mentioned that you were an ecotoxicologist. What does an ecotoxicologist do actually?

Dr. RODGERS: Well, as ecotoxicologists, we're interested primarily in the same thing that other traditional biologists might be interested in. If we back away from science and look at science, much of science is involved with stimulus and response. So the stimuli that an ecotoxicologist would be interested in would be those chemical, physical and biological entities in our environment that may pose risk, or have the potential to cause harm.

PALCA: I see. And are you seeing anything in today's ecosphere that would give you concern about perhaps killer algae…

(Soundbite of laughter)

PALCA: …forgive my use of the phrase, but algae being a danger at this point?

Dr. RODGERS: Well, it's interesting that you used the term killer algae because some of our friends in Spain and Russia have used the term assassin algae. So that's not too far-fetched. Around the globe, we're seeing extinctions of invertebrates. We're seeing the extinctions of fish. We're seeing attacks on birds and extinctions of birds, other wild animals such as monkeys and the rhinoceros on other continents. We're seeing plants declining as a result of these toxins, and impacts on domestic animals like cattle, sheep and dog.

PALCA: I should correct something I said earlier. This paper that you published was not in PNAS but in Environmental Geosciences. And I apologize for getting that wrong.

Dr. RODGERS: Thank you.

(Soundbite of laughter)

PALCA: Okay. Let's take a call now and go to Matt(ph) in Wyoming. Matt, welcome to SCIENCE FRIDAY. You're on the air.

MATT (Caller): Hi. I just had a question. How long would it take for an algae to evolve again to be deadly? And could it happen again?

PALCA: Hmm. Well, that - yeah, that - we were sort of just discussing that. Is this something that we could see again, do you think?

Dr. RODGERS: Well, I think this is something that we certainly proposed. A lot of these algal - rapid algal growths and a lot of the mass extinctions are also correlated with global climate change. And so, we should certainly be alert. And it's certainly - this hypothesis gives us something to look at and look for as we go into the future.

PALCA: All right. And I'm just wondering, I mean, I know it's early days, but surely, you've presented this at meetings and so forth. What's been the reaction of people who think about things like mass extinctions?

Dr. RODGERS: Well, there's two sources of information actually. The - my colleague, Jim Castle, just presented this as one of the featured papers at the Geological Society of America meeting, and the reaction was incredible. He got a lot of very good feedback. He got a lot of supporting information, and obviously, a lot of questions. In my experience from the algal side and the toxicological side, I've certainly got a lot of feedback from around the world in terms of people with, what I call, biomarker information or biochemical information from the rock record supporting this hypothesis. So we are fast-pulling that information together to see - to bolster the support for this hypothesis.

PALCA: That's interesting because it sounds like you are certainly going to want to get some original data. But it sounds like there might be hints and clues and data that's already been collected that might be useful in proving or disproving this theory.

Dr. RODGERS: Absolutely.

PALCA: And if you do have - I mean, if you do had - if you had all the money that you wanted, what would be the first thing you'd do if you went out to get more data?

Dr. RODGERS: Well, I think we've got the correlation between the production of algae through stromatolites and through the rock record, and the incidence of mass extinctions in the past, down pretty well. I think we've got the other piece of information is, we have this pretty strong, is the information of the ongoing events right now. I mean, folks are tracking those fairly well. What we need to do, I think, next is go back in the rock record and look at some of these biomarkers, some of these biochemical forensic information, if you will, and go back in time and say, can we measure any residuals of some of these toxins. And certainly, the pigments are there from the algae. So perhaps, we can pick up some of the residuals from the toxin.

PALCA: Okay. Well, we have to leave it there. John Rodgers is professor of forestry and natural sciences, and the director of ecotoxicology program at Clemson University.

That's it for today. For NPR News in New York, I'm Joe Palca.

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