The Mystery of Sea Creatures (5/5): The fantastically weird world of photosynthetic sea slugs | Michael Middlebrooks

**Elise Hu** (0:00)
It is summer where I live, and luckily, I live near the Pacific Ocean. As the weather continues to heat up, I'm spending more time at the beach. It always makes me wonder, what's going on under the water? From the deep sea to the shoreline, the ocean is teeming with creatures that are stranger, smarter and more surprising than most of us could ever dream up. For July's TED Talks Daily playlist, we have gathered five of our favorite talks that dive into the awe-inspiring and occasionally mind-bending creatures from orcas to kinky fish that live beneath the waves. Happy listening.
You're listening to TED Talks Daily, where we bring you new ideas to spark your curiosity every day. I'm your host, Elise Hu. Today's talk takes us into the vast depths of the ocean and explores creatures I have to admit I knew very little about, but are totally fascinating. Sea slugs. They're beautiful, diverse, interesting, and in his 2022 talk from TEDx PSU, zoologist Michael Middlebrooks gives us a deep dive into these fascinating little invertebrates after a short message.
And now, our TED Talk of the day.

**Michael Middlebrooks** (1:25)
I'm gonna talk to you today about sea slugs and solar power. My background, and what I do, I'm an invertebrate zoologist. So invertebrate animals are animals that don't have a backbone. So this is actually most of the animals on the planet. It ranges from things like insects to clams to sea sponges to worms, and a great and other many things that we don't have time to talk about today.
On our planet, most of the biological energy that we have available comes ultimately from the sun. The process from this being converted to solar energy to biological energy is photosynthesis. You're probably familiar with this as something that plants do.
And all of the food that we eat ultimately comes from photosynthesis, either us directly eating plants or eating animals that eat plants. And that's really where all of the energy all of the animals comes from.
However, there are a few animals that have managed to get around that and become photosynthetic themselves and are able to capture the energy from the sun, convert it into biological energy, right? So just like plants, they take carbon dioxide and sunlight, turn it into sugar and oxygen.
The best and most famous example of this are the corals.
Corals are able to photosynthesize because of a special partnership, a symbiosis that they have with a single-celled algae called zooxanthellae. The algae live inside of cells of the coral, capture the sunlight and provide the corals with sugar. So effectively, we have photosynthetic animals. This is unusual, but actually occurs in quite a lot of the corals and many of their relatives, and actually happens in a fair number of other animals, as well. So we see this in things like some sea sponges, we see this in some flatworms, and we see it in other animals closely related to corals, like sea anemones and jellyfish. So this is an upside down jellyfish. This is an organism that, just like the corals we were talking about, has these zooxanthellae inside of them and can photosynthesize. So this animal lives in shallow mangroves throughout the world, and just lays on the bottom capturing sunlight. I keep a few in my laboratory that I use for teaching, and I don't actually have to feed them. I just give them light from one of my aquarium lights, and I've managed to keep some of them there for two years, and I use them in my invertebrate zoology courses. I like the jellyfish though, even though the coral is perhaps a more famous example. The jellyfish is nice because we can take the tentacle of a jellyfish and look at it under the microscope, and that allows us to see this process. It's quite remarkable that we have animals that are not doing the typical animal thing. The jellyfish can still feed it in the wild, they do, but they can get most of their energy just from the sun. Fantastic. I primarily study a group of organisms called mollusks. Mollusks are probably familiar to some of you, if because of the, nothing else, because of their shells and in some cases as food. So these include animals like snails and clams, also things like octopus and squids and some other strange things that we won't have time to go into today. But the mollusks are a fantastically diverse group. They are the second most diverse group of animals on the planet after the arthropods, which went out because of the insects. But in terms of sheer diversity in body form, the mollusks, I would argue, are in fact the most diverse and range from things smaller than grains of rice to colossal squids that are absolutely enormous.