Catching Up on Sea Slug Science

IRA FLATOW: The waters off Northern California are becoming warmer due to global warming, and scientists are still trying to untangle the consequences. But one thing they have noticed is all sorts of animals that aren’t, are not, usually seen in the area.

One of these animals is a sea slug called the Hopkins’ rose. If you’re imagining a slimy brown slug you find in your garden, think again. My next guest is here to open your mind to the diversity. There really is tremendous diversity in these little creatures. And he’s going to give us an update on the latest in sea slug science.

Terry Gosliner is a Senior Curator of Invertebrate in Zoology, Geology at the California Academy of Sciences in San Francisco and he joins us from KQED there. Welcome to Science Friday.

TERRY GOSLINER: Well, thank you very much.

FLATOW: Is there a definition for what a sea slug is?

TERRY GOSLINER: Well, a sea slug is basically a marine snail without a shell, and they’re tremendously varied and live in every part of the ocean.

FLATOW: Is it related to the garden slug?

TERRY GOSLINER: They are distant cousins of the garden slugs, yes.

FLATOW: So what are they? Nudibranch, a nudibranch.

TERRY GOSLINER: Well, that would be a more formal name for a sea slug, and a nudibranch means that it has a naked gill. The gill is not surrounded by the shell.

FLATOW: Now, the Hopkins’ rose is usually found in Southern California, but as I’m saying, you’re seeing an increase where you are in San Francisco. Is that a problem?

TERRY GOSLINER: Well, the presence of the nudibranchs is not a problem in itself, but the cause behind it is where the problem is, and that is that unusually warm waters are being found off our coast. And while we’re really enjoying seeing so many of these unusual slugs that are usually a rare treat in the Bay Area, it’s reflective of much warmer ocean conditions and other organisms are suffering as a result of those warm waters.

FLATOW: How are they suffering? The other–

TERRY GOSLINER: Well, one of things we’re finding, for example, is that a lot of sea birds, like the Cassin’s auklet have been dying in large numbers because there’s just not enough food, because the warmer water also means that it’s less nutrient rich.

And other things like there’s been a lot of California sea lion pups coming ashore emaciated in the last several weeks because again, there are not enough fish to feed on because the water’s warmer.

FLATOW: That’s quite interesting. Let’s talk about the sea slug for a moment, the Hopkins rose and the other sea slugs. They are not, as I say, the typical garden variety, the ugly ones that you see. These are quite beautiful aren’t they?

TERRY GOSLINER: They’re strikingly beautiful and they are abundant in psychedelic colors. The Hopkins’ rose in itself is a bright hot pink with lots of finger-like projections sticking out of its back. It’s about a half an inch to an inch in length. And you can’t miss it when you see it in a tide pool. You can see it from 10 yards away because it just looks like this bright pink rose in an otherwise dark backgrounded tide pool.

FLATOW: I’ve seen pictures of sea slugs that they look like they have little tentacles and things, like spikes coming off of them.

TERRY GOSLINER: They have sensory organs on the head. They have a gill on the back, for the most part. And they have lots of projections that can detect changes in their environment, and detect their food, and the presence of members of their own species with which they can mate.

FLATOW: There was a study that came out this week that showed a sea slug can actually steal genes from algae. Wow. What does it do with that? How does it do that? What does it do with the genes?

TERRY GOSLINER: Well, there’s one group of slugs that feeds exclusively on marine algae and they are able to retain the chloroplast, the photosynthetic organelles of the algae they feed on. And some of them not only do that, but they, through a process that we call horizontal gene transfer, they can take part of the DNA of the algae and use that to help manufacture their own photosynthetic products.

And so they’re really very clever organisms in terms of the adaptations they have for survival. So if food disappears from their environment, they can actually produce their own food through the genes that they acquire and the chloroplast that they get from the plants they feed on.

FLATOW: So they’re actually farming algae in their own tissue.

TERRY GOSLINER: They are.

FLATOW: Wow.

TERRY GOSLINER: Yes, exactly.

FLATOW: And that’s the food they’re making. It almost sounds like coral, you know? What coral do with algae.

TERRY GOSLINER: It’s exactly the same kind of thing. And we find a lot of marine organisms, and particularly organisms in the tropics, have this symbiosis between algal cells and harbor them in their tissues. And some of them get up to 50% of their nutrition from the photosynthetic products of their algae.

FLATOW: Do they pass this on? I mean, their offspring once they take over this DNA?

TERRY GOSLINER: There’s some evidence based on the fact that there are chloroplasts in the eggs of the nudibranchs that they are able to pass them on. But we also know that they can acquire them when they’re adults and juveniles.

FLATOW: Now there is a sea slug called Glaucus Atlanticus that has an interesting defense. Tell us about that.

TERRY GOSLINER: Yeah, it floats around in the open ocean in tropical oceans and it’s able to float because it swallows a big air bubble. And it feeds on the Portuguese Man o’ War.

And what it does is it’s able to take the stinging cells of the Portuguese Man o’ War and use it for its own defense and fire them at will. And so these things often wash up on tropical shores and people inadvertently see this bright silver and blue thing on the beach and pick it up, and they get the same sting that they would if they’d picked up a Portuguese Man o’ War.

FLATOW: And that is painful, I can tell you from personal experience.

TERRY GOSLINER: It’s no fun.

[LAUGHTER]

FLATOW: This is Science Friday from PRI, Public Radio International. You know, we just think that this is a fascinating world of sea slugs. Are any of these sea slugs the kind that Eric Kandel used to study in his famous nervous system studies that he won the Nobel Prize for?

TERRY GOSLINER: They are exactly some of the same things. Those are sea hare’s that have giant nerve cells. And that’s why they’re so appropriate for neural physiological studies as you can stimulate individual cells because they’re so large. And it’s allowed us to look at primitive nervous systems as a model for understanding the evolution of more complex systems, like our own.

FLATOW: I think he give us a new appreciation. I’m sure you’ve gotten that appreciation a while back, as you studied sea slugs.

TERRY GOSLINER: Absolutely.

FLATOW: Yeah, do you have a favorite one?

TERRY GOSLINER: I have a favorite one, and it changes almost daily as soon as I see another new one that we discover. And that’s what makes it so exciting, is that there’s always new discoveries and new insights into these amazing organisms that are great indicators of climate change and environmental sensitivity.

FLATOW: Wait, so the sea slugs are sort of the canaries of the oceans.

TERRY GOSLINER: Well, that’s what we feel. And because they are, like the Hopkins’ rose, suddenly becoming abundant, is an indicator of the warmer water. We also see the cycles that they go through, the way they extend and retract their ranges in response to warming and cooling conditions in the ocean. So they’re really good indicators of changing environments.

FLATOW: I see you have a very boring job.

TERRY GOSLINER: Oh, it’s terrible, I hate it.

[LAUGHTER]

FLATOW: Somebody’s got to do it. Well, I’m glad you took some time to share your love of sea slugs with us. We don’t get that often, you know. Sea slug aficionados.

TERRY GOSLINER: It’s my pleasure.

FLATOW: Terry Gosliner is a Senior Curator of Invertebrate Zoology and Geology at the California Academy of Sciences in San Francisco. May all your sea slugs be beautiful.

TERRY GOSLINER: Thank you very much.