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PRI's Environmental News Magazine

Marine Plants That Flee Predators

Air Date: Week of October 5, 2012

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Suzanne Menden-Deuer

Scientists at the University of Rhode Island have discovered an ocean algae behaving more like an animal than a plant. These common phytoplankton can swim away from predators, as oceanographer Susanne Menden-Deuer told host Steve Curwood.


CURWOOD: It's Living on Earth - I'm Steve Curwood. Plants are capable of incredible things: they supply the earth with oxygen, sequester carbon dioxide, and provide us with shade on a hot sunny day. And now, scientists at the University of Rhode Island have uncovered a surprising new talent in a group of tiny ocean plants—the ability to run away. This remarkable discovery was made by Susanne Menden-Deuer, Professor of Oceanography at the University of Rhode Island. Welcome to Living on Earth!

MENDEN-DEUER: Hi, I’m glad to be here!

CURWOOD: So, what kind of plant is this that can swim away from its predators?

MENDEN-DEUER: This phytoplankton species is a plant-like organism and it functions a lot in the same way in that it photosynthesizes. It takes the sunlight’s energy and inorganic carbon and produces organic carbon like sugars and the oxygen that we breathe.

CURWOOD: Now, these are really tiny, they’re kind of like algae?

MENDEN-DEUER: Exactly. They’re microscopic algae and even though they’re microscopic, they’re so numerous… most of our planet is covered by water… by ocean water, and so the power of these numbers and the large area covered results in these microscopic organisms having a tremendous impact on our earth’s ecosystem. They generate about half of the oxygen that is breathable in the atmosphere. So, what I would encourage your listeners to do is to say thank you to the phytoplankton every other breath they take.

CURWOOD: (Takes breath). Thank you phytoplankton!


CURWOOD: Now, please describe the specifics of this study. How do you figure out that a plant in the ocean is running away?

MENDEN-DEUER: Well, my lab works on predator-prey interactions. We’re really interested in who eats who. We were trying to figure out if these predators can distinguish between food that is nutritionally valuable to them and food that’s less nutritionally valuable, or less good. So, can it distinguish between - say a salad and a bag of Doritos, for example.

CURWOOD: (Laughs.) And what kind of predators are these?

MENDEN-DEUER: These are all single-celled predators. They’re just about the same size as their food, they’re just about as numerous as the phytoplankton. And, in the last 20 years or so, people have discovered that they are very voracious eaters of phytoplankton.

CURWOOD: So, what did you discover in terms of the ability of the phytoplankton to get away from these guys that want to gobble them up?

MENDEN-DEUER: What we do is we use stereo-video cameras to image in three dimensions how these organisms move. And we do different kinds of incubation. Sometimes we just have the algae in the tank, sometimes we have just the predator, and sometimes we put both of them together. And by looking at the differences in behavior when they are together and when they are separate, we can tell if things like do they respond to each other.

We also do numerous control experiments where we simply take, for example, the wash water from the predators. So, they’ve left some chemical scent… maybe they pee in the water… and then we expose the algae to that. So we can say specifically, do the algae respond to just the chemical scent?

CURWOOD: And what exactly did you discover?

MENDEN-DEUER: What we discovered was that any kind of indication that a predator was present or had been present previously, induced the algae to swim away. And we structured our water column like we find structure in the ocean in that there are different salinities at different depths. In this case, the algae is very tolerant of low salinities whereas the predator is not.

In our experiment, if the algae could reach an area of low salinity, we call that the low salinity refuge, then indeed the algae could survive. If we force the predator and the prey together in one tank, we don’t allow the algae to swim away anywhere, then the predator will eat all of the prey within about one day. If we just have the algae by itself, it can double approximately every day. But if we have an algae that can effectively flee, it can double every other day in the presence of the predator. And that’s really a key finding of this study is that this fleeing behavior is very effective in increasing the survival of the algae.

CURWOOD: Is this behavior unique within the plant kingdom?

MENDEN-DEUER: As far as we know. We’ve done a thorough literature research on this and there are many examples of course of making chemical constituents that make them less palatable or toxic to predators. There are also well known examples of plants having morphological modifications such as spines and thorns that protect them predation, but we haven’t been able to find a prior example of any photosynthetic organism that has this kind of fleeing behavior.

CURWOOD: And what’s the name of this algae? I’m out of here algae, is that the name of it?

MENDEN-DEUER: Yeah, we should rename it! It’s called heterosigma akashiwo. And akashiwo, I believe, means red tide in Japanese.

CURWOOD: Ah. What do you think is the significance of these findings in the bigger picture of what happens in the oceans?

MENDEN-DEUER: As an oceanographer, when I go out to sea, I often look out at the ocean and think, “how are we going to figure this all out?” Because we have thousands of species that are interacting in a really dynamic environment. And here we can have these observations of microscopic cell-cell interactions that can really help us understand a large scale process such as how these phytoplankton live and survive. And I think that is really a highlight for me because it gives us hope that we can unravel the complexities of marine food webs.

CURWOOD: What’s next now?

MENDEN-DEUER: The next thing we would really like to do is look at other phytoplankton species. We don’t know if this is a common or an uncommon behavior. The species we were studying is at times extremely successful in the ocean at making very dense surface slicks that are visible from low-flying aircraft.

Part of what motivated our study is that we wanted to look at what makes this species so successful. So, we would like to look at other species to see, are they equally able to flee from predators, or is the success of the species that we studied partly due to the fact that it can flee from its predators?

CURWOOD: Suzanne Menden-Deuer is a professor of oceanography at the University of Rhode Island. Thanks so much for taking this time with us today.

MENDEN-DEUER: It was my pleasure, I was really glad to be here!



The fleeing Plant paper

A video of Suzanne Menden-Deuer in her lab


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