The High-Tech Lab Unlocking Secrets Of Coral Reproduction

FLORA LICHTMAN: I’m Flora Lichtman, and you’re listening to Science Friday.

[MUSIC PLAYING]

Today on the podcast, a conversation from our live show in Redwood City, California. Ira talks with the scientist growing baby corals to make reefs more resilient.

[MUSIC PLAYING]

IRA FLATOW: One of the unique pleasures about being in the Bay Area is the proximity to the ocean, close to marine wildlife. We love to see the whales and the dolphins and the sea lions. But there’s also unexpected marine life here and not where you might expect. Right in Golden Gate Park can find a lab on the cutting edge of growing coral. Scientists are discovering the secrets of coral reproduction in an effort to bring them back from the brink. I want to introduce you to one of these scientists. Dr. Rebecca Albright is a coral reef biologist and associate curator and Patterson scholar at the California Academy of Sciences. Welcome to Science Friday.

[CHEERS, APPLAUSE]

REBECCA ALBRIGHT: I’m excited to be here. Thank you, Ira.

IRA FLATOW: Were you always involved in the water? What drew you to being a coral scientist?

REBECCA ALBRIGHT: I’m sure I’m not the only person in this room that dreamed of being a marine biologist as a kid. I think I just stayed the course. I was always drawn to the ocean. I always felt very comfortable and at peace in the water. I was a competitive swimmer. In undergrad, I was pre-med, and I decided to study abroad in Australia. This was around the year 2000. And I wasn’t going to go to Australia and not dive on the Great Barrier, so got certified to dive. I’m from Ohio in the Midwest, and so that certification dive, it was in a limestone quarry.

IRA FLATOW: I did the same thing.

REBECCA ALBRIGHT: Yeah.

IRA FLATOW: In the spring, it was cold.

REBECCA ALBRIGHT: It was majestic, I’m sure. So our navigation dive was very much 20 kicks to the sunken school bus and then 10 kicks to the refrigerator. And then, I went from there to the Great Barrier Reef, and my first 60 to 70 open-water dives were on the Great Barrier Reef in around 2000, 2001. And I just never looked back.

IRA FLATOW: A lot of people see coral, but they see it in its white skeleton form, which you don’t really appreciate how beautiful it is. It’s a very charismatic creature, isn’t it?

REBECCA ALBRIGHT: In my completely unbiased opinion, yes. I think so. Yeah, I think one of the things that has really drawn me to corals is that they are these incredibly charismatic, complex organisms, but in a really unassuming and nonobvious way. If you look at this animal, most people actually don’t even understand that they are animals. Most people think that there are rocks. And when you take a closer look at them, you realize that they are these very sophisticated, very complex animals, the extent to which you can visualize this.

This is probably– this is part of a coral colony, an acropora colony, that is obviously no longer living. This is the white skeleton that was underneath. And when this animal was living, what there was a very thin veneer of animal tissue that coated and covered this skeleton, much like your thin tissue covers and coats your human bones. And what’s really fascinating about them is they’re colonial critters.

And so what this animal started life as was one tiny little sesame seed-sized larva that swam around in the ocean, no bones, completely just tissue. Swam around in the ocean, and then found a place to settle, metamorphose, and start calcifying. And then it asexually budded new mouths and started to grow over time, and then eventually formed a colony like this. Every single one of these tiny little bumps, millimeter to centimeter-sized, depending on the species, is a single polyp. And this animal started life as a single polyp.

IRA FLATOW: Wow.

REBECCA ALBRIGHT: And then, once it grows to this size, which this animal might have been about 8, 10 years old, they’re all sharing resources and communicating within this animal that allows it to exist as one singular organism. So they have canals inside of their skeleton and their tissue where they’re sharing resources, shunting nutrients to one another. It’s really quite a sophisticated and beautiful process.

IRA FLATOW: And this was once a beautiful, colorful animal, which is now bleached white skeleton.

REBECCA ALBRIGHT: Yes.

IRA FLATOW: What causes that?

REBECCA ALBRIGHT: Well, in this case, I just bleached it. But in–

[LAUGHTER]

–nature, the concern with coral bleaching worldwide right now is that it’s a stress response. And coral bleaching is a stress response to pretty much any stressors. Coral animals can stress bleach in response to salinity stress or cold water or light stress. The elephant in the room at this point in time is global warming and warming of the oceans, causing global mass bleaching, where what we’re seeing are the majority, 84% in the current one that’s happening, 84% of the reefs worldwide bleaching at the exact same time. And obviously, that shouldn’t be happening.

And what happens is that the animal tissue that coats this is also this very interesting and sophisticated relationship with a symbiotic algae that lives inside of its tissue. And if you think about corals and coral reefs, they live in these beautiful, clear waters. And the reason those waters are so crystal clear is that there’s not a lot of nutrients in that water column.

And so in order to get food, what corals have figured out over hundreds of millions of years is to take on these algae and engulf them into their own cells and have them photosynthesize in warm, high-lit waters and then steal the sugars. And so the algae provide up to 90% of the food requirements for the animal. And when the water gets too warm, what happens is they expel the algae. And in doing so, they’ve just lost their primary food source. So they can effectively starve to death.

IRA FLATOW: Wow.

REBECCA ALBRIGHT: And the algae gives it its color. So when it loses the algae, it looks like you have taken it and dipped it in bleach.

IRA FLATOW: And your job in your lab is to try to save the coral that we have alive now?

REBECCA ALBRIGHT: We’re doing our part. There’s a lot of people trying to tackle this wicked problem from a lot of different angles. One of the ways that we are trying to address this problem is figuring out how to get corals to reproduce in captivity for a few different reasons, one, just as a fundamental model organism that we can study coral reproductive biology. We want to be able to utilize that content and knowledge as a biobanking in kind of a Noah’s Ark so that we can replace things that are lost in the wild. And we also utilize it as an opportunity to develop new restoration techniques that we can port to on-the-ground restoration efforts in the wild.

IRA FLATOW: How many other labs do you think around the world are doing this kind of work?

REBECCA ALBRIGHT: It’s definitely gaining traction. We were the second in the world to do it in 2018. And now I would say there’s probably 50 or 60 worldwide. So it’s definitely accelerating in terms of its importance and prevalence throughout the world really quickly.

IRA FLATOW: Let’s talk about coral reproduction. You brought a slide of coral spawning. What is happening?

REBECCA ALBRIGHT: So corals can reproduce asexually and sexually. So asexually, what a coral will do is you can break off a branch. And just like a starfish, that coral will produce a new branch, and the branch will produce a new coral. But you’re only propagating a single genotype. So sexually, the way that corals reproduce is by releasing sperm and eggs into the water column. And typically, this is once a year. They’re what we call broadcast spawners. Most coral species, about 75% of them worldwide, are hermaphroditic, so they have both eggs and sperm in the same colony.

IRA FLATOW: That’s convenient.

REBECCA ALBRIGHT: It is, except they don’t self-fertilize.

IRA FLATOW: Oh, they don’t.

REBECCA ALBRIGHT: No, so you still have to have a partner.

IRA FLATOW: I see. Does this happen every month like clockwork, so to speak?

REBECCA ALBRIGHT: Once a year, usually.

IRA FLATOW: Once a year.

REBECCA ALBRIGHT: Yes. In most places, it’s late summer after a full moon and a few hours after sunset.

[LAUGHTER]

IRA FLATOW: Sounds very familiar.

[LAUGHTER]

I’m going to ask, how do you get them to spawn, smooth jazz music, or how do you do that?

REBECCA ALBRIGHT: So we have stood on the shoulders of some researchers in London that have taken the body of literature that’s tried to figure out the hierarchy of environmental cues that elicit this once a year event and winnowed it down to basically three things. We have to mimic seasonal cycles because it happens in summer, late summer. So these animals have to experience a summer and a winter.

So we keep them in systems where every single day we’ve programmed in that the water temperature is iteratively changing, getting warmer in summer and then cooler in winter. And then we also have LEDs with different wavelengths of light where we have to simulate sunrises and sunsets. And we have blue LEDs and white LEDs where we mimic lunar cycles. And in doing those three things, we have been successful in getting these animals to spawn at the exact same time that they do in the wild in Australia.

[APPLAUSE]

IRA FLATOW: Yeah.

FLORA LICHTMAN: We have to take a quick break, but don’t go away. More on this when we come back.

[MUSIC PLAYING]

IRA FLATOW: So in this lovemaking tradition here, do you help them along? Do you catch the spawn? You do. Show us what you mean by that.

REBECCA ALBRIGHT: We do. So we have these nets, very sophisticated. This is a painter’s net from Home Depot. And what we do is in order to– so it’s very much like IVF, coral IVF, to be honest, because right now many coral populations in the wild have become so depauperate that even if they do spawn synchronously, which a lot of times that process is breaking down in the wild, they might be so few and far between that the probability of those gametes meeting up and successfully fertilizing and making new corals is very low.

So there are assisted reproductive efforts where we go out in the wild diving at night or in the lab. And we take these, and we just cover the coral colony when we know it’s going to spawn. And then when it does spawn, the gamete bundles, which are bundles that have both egg and sperm in them, have a lot of lipids, a lot of fats. And so they’re very buoyant.

So they will float up into this little collector tube, a Falcon tube. And then when it’s done spawning we can note what genotype it is, what species it was. And we can take this off, cap it off, take it back to the lab, and then cryopreserve it for biobanking. We can fertilize things and make new genotypes that probably wouldn’t happen in the wild. And then we settle the coral larvae, and we can outplant them back to the reef.

IRA FLATOW: So it’s basically you’ve created a homemade– looks like an inverted funnel with a net on it.

REBECCA ALBRIGHT: It is. Yes. Sophisticated.

IRA FLATOW: Well, whatever works. I’m a big MacGyver person myself, and that looks like what you’ve gotten there. So how do the coral, when they’re out in the wild, how do they know where to land? If they’re spawning or they’re very tiny, how do where to go?

REBECCA ALBRIGHT: Yeah, it’s a great question, and I don’t think we fully understand all of the details and mechanisms of that. But basically, once a coral larvae exists, you can imagine this tiny little sesame seed-sized thing that’s in the big, wide ocean trying to find a place to set up home. For some corals, the biggest one we know of is over 500 years old in American Samoa named Big Mama. And so you want to find a place– it’s an irreversible decision. So you want to find a place that is a really good home for the next 10 to 100 years.

And so even though these larvae look so simple, they are actually packed with receptors, chemoreceptors, photoreceptors, neuroreceptive cells. And they swim around. They have two ends. There’s an oral end of the larvae and an aboral end. And the aboral end is packed with receptors. And so they swim with that aboral end first through the water column. And they will actually swim down to the bottom and probe it. It’s really fascinating to watch via microscopy.

They probe the bottom, and if they don’t like what they find, which a lot of studies indicate that it has to do with the microbial environment that’s on the substrate and the crustose Coralline algae. There’s a certain species of algae that they like that’s indicative of good reef health. If they don’t like it, then they just swim up, and they’ll go find some place else and probe again. If they do like it, then that aboral end will start to get fixed to the bottom. It will start to calcify. And it’ll start to metamorphose into the oral end that’s up, differentiates into polyps and a mouth and will then start to feed and asexually bud new mouths.

IRA FLATOW: Do you have to reproduce all this?

REBECCA ALBRIGHT: No, they do that part on their own.

IRA FLATOW: Just dance?

REBECCA ALBRIGHT: Oh, no.

IRA FLATOW: No.

REBECCA ALBRIGHT: My coral dance.

IRA FLATOW: Your choral dance, it was kind of interesting. How do you know in your lab if you’ve been successful at what you’re doing?

REBECCA ALBRIGHT: Yeah, it’s a great question. And there’s many different parts to that question, particularly with broadcast spawners because there are many bottlenecks. And so ultimate success is lots of coral juveniles that are– so the biggest success we have had so far was getting our corals to spawn, fertilizing babies, getting the larvae to settle, and then rearing them out for three to four years so that they become reproductively viable and then start spawning with their parent generations. That was the ultimate success, and then getting an F2, or a second generation.

IRA FLATOW: Is this out in the wild, or is this in your lab?

REBECCA ALBRIGHT: This was in the lab.

IRA FLATOW: Still in the lab.

REBECCA ALBRIGHT: Yes.

IRA FLATOW: Do they ever get out into the wild.

REBECCA ALBRIGHT: So we are not permitted right now. So corals are regulated by CITES, which is the Convention on International Trade of Endangered Species. They’re very heavily permitted. And at this moment in time, we are not permitted to– it’s illegal to take them from an aquarium and put them back out into the wild. So what we do is we try to port the ideas and the concepts.

And so we have a partnership right now with the Roatan Marine Park in Honduras, where we have built a lab just like the one in San Francisco down there in Roatan so that they can do this on their reefs in their backyard. That’s another metric that was really meaningful in terms of success for us. And so that lab opened in June, and we’ve now done two spawning events there. In June, we were able to outplant over 3,000 baby corals, brain corals back out to the reef. And the team is actually down there right now with some star corals doing the exact same work.

IRA FLATOW: Is it possible to find corals that are resisting climate change and are able to survive and bring them in the lab and reproduce them?

REBECCA ALBRIGHT: Yeah, that is something that people are tackling from different angles. So there are people that go out after a bleaching event. People sometimes do aerial surveys after a bleaching event and find the survivors. And then we’ll go preferentially either take tissue samples to see what was it about that individual that made it resilient, or take fragments of it and preferentially asexually propagate it in a coral farm or a coral garden. Another thing that we’re doing in our lab is when you have these pools of larvae, very early in life, with the most number of individuals and the most genetic diversity, expose them to a heat stress and try to select for the survivors, and then breed those out with the thought that they might be able to withstand a bleaching event later.

IRA FLATOW: And I want to get this youngster who has a question. Yes, go ahead.

AUDIENCE: How many creatures depend on the coral for life?

REBECCA ALBRIGHT: How many creatures depend on corals?

AUDIENCE: Yeah.

REBECCA ALBRIGHT: I’m so glad you asked that question. So about 25% of all of the life in the oceans is supported by coral reefs.

IRA FLATOW: Wow.

REBECCA ALBRIGHT: So a quarter of all marine life is dependent on coral reefs.

IRA FLATOW: Do you think you love your job a little?

REBECCA ALBRIGHT: I love my job. I’m very lucky. I don’t take that for granted.

IRA FLATOW: Yeah, bet you do. Well, Dr. Rebecca Albright is a coral reef biologist, associate curator and Patterson scholar at the California Academy of Sciences. Thank you so much for coming on the program today.

[CHEERS, APPLAUSE]

[MUSIC PLAYING]

FLORA LICHTMAN: Thanks for listening. Don’t forget to rate and review us wherever you listen. It really does help us get the word out and get the show in front of new listeners. Today’s episode was produced by Kathleen Davis. I’m Flora Lichtman. Thanks for listening.

Copyright © 2025 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/