Jellyfish are the oldest animals in the ocean—they’ve been swimming on our planet for more than half a billion years. But it is only recently that scientists have begun to understand these beautiful but deadly organisms, from the sophisticated way they propel themselves to the complex chemistry involved in their phosphorescent glow. The picture that emerges, according to Juli Berwald, author of the new book Spineless, is of an “incredibly well-adapted, super-elegant creature.”

Speaking from her home in Austin, Texas, Berwald, who has written for National Geographic, explains how the jellyfish’s glow revolutionized genetics; why robots are copying jellyfish; and how jellyfish are taking advantage of ocean acidification to expand their range and invade new waters.

View Images Courtesy Riverhead Books

The highlight of our summers on Long Island is when the moon jellies bloom and we get phosphorescent water at night—jellyfish can make the sea a magical place. Is that why you fell in love with them?

It wasn’t actually their beauty that initially got me into it. I was writing captions for a National Geographic story about acid seas by Elizabeth Kolbert. In that story there was a graphic showing the winners and losers in a future acidified ocean. Looking at the losers first, it was all things with shells, which dissolve in higher acidity. The winner side was things like algae, microalgae, kelp, and jellyfish. I thought, “Really? Do we know that for sure?”

My PhD is in ocean science, so I love to look into the scientific literature. I dug in and found there was this excitement and controversy in the literature about jellyfish and how their abundance was increasing in today’s damaged oceans. I thought, “This is interesting.”

In terms of a muse to write about, they live on this line that is both angelic and demonic and nothing about them is clear-cut. They are absolutely gorgeous to look at and, you’re right, their bioluminescence is astonishing!

But their sting is vicious! They may not just ruin your time at the beach. Some are actually deadly. The box jelly, the very toxic one that lives in the Pacific Ocean, can kill a man in three minutes and contains enough sting for 60 men. Unfortunately, because of climate change, its range is expanding down the coast of Australia into the Gold Coast, where there are popular surfing beaches.

What can these apparently simple creatures tell us about evolution?

They’ve existed for well over half a billion years. They are certainly the oldest swimmer that still exists on our planet. There are roughly 200 species of the true jellyfish, but as we do DNA analysis we’re finding a lot of cryptic jellyfish. There’s probably another two thousand hydrozoan jellyfish, which is a cousin group.

Jellyfish can be as small as a few millimeters across, like the size of an eraser on a pencil, or as big as 500 pounds. And they’re not all clear. The larger ones, in particular, have developed pigments. A lot are red because, as you go down in the ocean, the red light disappears and they appear black, like a burglar wearing all black to avoid detection. Some are incredibly beautiful. One I saw in Japan has aquamarine disguise on top and maroon disguise on the bottom.

The fact that they’ve been around so long says that they’ve come up with a morphology, body structure, and adaptation to survive, hunt, and avoid being eaten, which is supremely elegant. In my opinion, it all comes down to the speed and force of their stinging cells, which are a masterful piece of biological evolution that explode with a force five million times the acceleration due to gravity.

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The way jellyfish propel themselves through water is fascinating. Tell us about the extraordinary technology known as Robojelly.

When we think about walking on Earth, we think about pushing backward and creating a high pressure behind our foot. Jellyfish create a low-pressure system above their bell, which is stronger than the high-pressure system behind the animal, so it sucks itself through the water. When scientists started looking at other animals like lamprey eels, they found the same thing: a low-pressure system in front of the wiggle, which sucks the animal through the water.

Robojelly is a robotic jelly made out of silicon and these things called “actuators,” which are like fake muscles that contract. The initial idea was to see if you could create an undersea robot that moves through the water like a jellyfish. Now there’s a group building one that’s the size of a person and five feet wide. The idea is that it would sit deep in the ocean and report back, like a spy, and remain there for long periods of time, using very little energy.

View Images Two moon jellies swim at the Shark Reef Aquarium in Las Vegas. Photograph by Joel Sartore, National Geographic Photo Ark

You write, “GFP may be the most evolutionary successful gene of all time, it is even used as a biotechnical tool now.” What is it?

GFP is green florescent protein. Osamu Shimomura had been working with researchers at Princeton in the sixties to understand the jellyfish’s glow. He was able to purify the molecules that create the glow in the jellyfish, which are known as luciferin, luciferin being the enzyme. The glow was blue, but when jellyfish glow in the ocean, they’re green, so they found there was another molecule called GFP that takes the blue light and shifts it to green.

That protein was then studied by two other scientists, Martin Chalfie and Roger Tsien. They discovered that, almost like you would attach a note to the beginning of an email, you could attach the genetic code for that GFP to the front of a gene to figure out what it was doing in an animal. The green glow would report when that gene was turned on by the animal.

GFP has revolutionized biotechnology. It’s been inserted into yeasts, rabbits, mice, brains, and was modified so that it reported not just green but lots of colors, like red, blue, and orange, so you could study the way many different genes were working in one organism. These three men received the 2008 Nobel Prize for Chemistry for their work.

View Images Bioluminescence in jellyfish like this comb jelly provided scientists with a tool to understand genetics. Photograph by JASON EDWARDS, Nat Geo Image Collection

My wife loves jellyfish salad and you clearly do, too. What other cultures—and creatures—like to eat jellyfish? And what does jellyfish actually taste like?

It’s been eaten in Asian countries for a thousand years. In order to eat it you have to remove the water fairly quickly because otherwise it will spoil, as bacteria live in water. In Asia, they remove it by soaking it for about a week in a combination of salt and alum. They then rehydrate it to rinse the alum and salt out.

You don’t have to cook it. You just slice it up and eat it as a salad. It has a crisp texture and not much flavor. But if you add soy sauce, vinegar, and some sugar, it tastes a lot like a crispy seaweed salad. It’s quite high in protein and extremely high in antioxidants.

Some people in Asia see it as medicinal, to treat rheumatoid arthritis because it’s all collagen. It’s also being investigated for its nutritional properties, especially in Italy. The problem is that alum is not so great for you. It’s got aluminum in it which has been associated with Alzheimer’s, so they’re looking for new ways to preserve it without soaking it in alum salt. A Danish woman has come up with a method using alcohol to suck the water out and has created these jellyfish chips.

When I started working on the book, people didn’t realize how many different creatures eat jellyfish because the main way we look at what-eats-what in the ocean is by looking at gut contents, i.e. catching a fish, slicing its gut, and looking at what you see. You’re never going to see jellyfish!

But using DNA technology, we’re finding more and more creatures eat jellyfish. Leatherback turtles and the biggest bony fish in the sea, the Mola mola, live almost entirely on jellyfish. Recently we’ve discovered that penguins and albatrosses eat a lot of, and love, jellyfish. So jellyfish is on the menu for a lot of creatures in the ocean.

View Images Sea walnut jellyfish rest in the water at the Gulf Specimen Marine Lab and Aquarium in Florida. Photograph by Joel Sartore, National Geographic Photo Ark

The Suez Canal has become a route for invasive species moving between the Mediterranean and the Red Sea. Marine protected areas are also vulnerable. Talk us through the issues here.

The shipping industry is moving jellyfish around the planet. When ships take on ballast water, they can take on jellyfish as well, and then dump them out in a new place that may be hospitable to jellies. So, you can get big invasions like what happened in the Black Sea with the comb jelly, which took down the entire ecosystem there.

The rhopoema nomadica, or nomadic jellyfish, is native to the Indian Ocean but in the eighties, they started turning up in the eastern Mediterranean, presumably through the Suez Canal. Now this jellyfish forms massive plumes, kilometers wide, along the coast of the eastern Mediterranean and Israel. For the first time, recently, a huge plume formed off Egypt’s coast, and off Turkey and Lebanon. It’s a bad stinger. When it blooms intensely, it can get sucked into the watering systems that power plants use to cool machinery. Jellyfish are gooey, like a sink stopper, and clog the intake systems, so they have to shut down power plants until they can clear the bloom away.

Marine protected areas, which are like national parks on land, are seen as an important way for us to protect the richness, biodiversity, and health of the ocean. Because there are no fences, fish will find sanctuary and there will be a spillover effect outside the sanctuary where fishing is allowed, causing catches to actually increase. But invasive species can also go into the marine protected areas and take advantage of what’s there, as happened in Italy recently. This is not to say we should not have marine protected areas! It’s more complicated.

Some scientists say we are in the planet’s sixth major extinction and, if we aren’t careful, jellyfish are in place to take over whole ecosystems. Are we about to enter the age of the jellyfish?

This is such a hard question because it can tend toward fear mongering and sensationalizing. I also feel uncomfortable with that because we can’t predict where and when jellyfish blooms will occur. Jellyfish have been systematically neglected by science and the media for most of the 20th century because our understanding of the ocean is biased towards what is pulled up in nets: hard, rigid things. But jellyfish science is now reaching this explosive period of understanding.

Can they survive acidification? There are places around the world where we see sustained blooms of large jellyfish, like the eastern Mediterranean, the coast of Japan or Namibia, where ecosystems have become dominated by jellyfish. But, globally, I’m not willing to say that we know what’s going on. The ocean needs a lot more of our attention, and a lot more study. Jellyfish are very complicated. We don’t understand them. That’s part of what makes them so fascinating.

This interview was edited for length and clarity.