The Bizarre and Disturbing Life of Sea Cucumbers

Photo © Justine E. Hausheer / TNC

Globular denizens of the ocean floor, sea cucumbers are not much to look at. But for some reason I find them endearingly uncharismatic.

They have no faces, or even eyes, just a digestive tract with a hole at either end housed in a body that resembles a well-formed turd. (And is also unavoidably phallic.) And their entire life revolves around sucking up the seafloor and pooping it right back out again.

You honestly couldn’t design a less-interesting animal if you tried. And yet still I love them, because they manage to be absolutely fascinating despite their utter lack of charisma.

Why, exactly, are they so interesting? Well…

  • They projectile-poop their own organs onto predators

    Photo © Pierre Pouliquin / Flickr

    It’s hard to imagine that anything — including humans — would actually want to eat a sea cucumber. And yet they have several predators, from fish to sea turtles to people. Unfortunately, sea cucumbers come up a bit short when it comes to self defense. Some species, like the sandfish, spend the day buried in the sand as a lame attempt at camouflage.

    Others take a different route and projectile-poop their own internal organs all over any would-be predators — or curious science writers — that prod them a little too vigorously. They then simply re-grow whatever organs have gone missing.  

  • They breathe through their butt

    Sea apple sea cucumber, Pseudocolochirus violaceus. Photo © budak / Flickr

    No, really. I am not kidding. All species of sea cucumber breathe by dilating their anal sphincter to suck water into their rectum, where specialized structures called respiratory trees — butt lungs —  extract oxygen molecules from the water.

    If that fact alone doesn’t make you love sea cucumbers then you’ve officially lost your childlike sense of wonder.

  • They let fish live inside their anus

    A pinhead pearlfish, Encheliophis boraborensis. Photo © orangkucing / Wikimedia Commons

    And here you thought you were done reading about sea cucumber butts.

    Several species of parasitic pearlfish actually live inside sea cucumber bums. After smelling their way to an ideal host, the pearlfish swims head-first into the void. As the sea cucumber pumps water in and out to breathe, the fish slowly but surely wiggle their way inside. (Other pearlfish take the opposite approach, reversing in tail-first.)

    Some pearlfish species are harmless, simply bumming a free room from the sea cucumbers. (Pun intended). Presumably it’s not ideal to have a fish up your butt, but it could be worse. Oh so much worse… as other pearlfish species eat the sea cucumber’s gonads from the inside.

  • They absolutely infuriate scientists

    A feather-mouthed sea cucumber, Synapta maculata. Photo © Bernard Dopont / Wikimedia Commons

    You’d think that a shuffling little mobile colon would be fairly easy for scientists to study, right? Guess again.  

    Scientists have found it nearly impossible to track sea cucumber movements. If you stick a tag or tracking device in them they just extrude it out from their skin. Dye or scaring to mark individuals? Both disappear. As one scientist put it: “They just don’t want to be studied… which is funny because it should be as easy as studying trees.”

    Even trying to work out something as simple as growth rates is a challenge, because it all depends on their environment. Take two individuals of the same species and age, put them in different places, and they could grow at different rates.

    And then sometimes they shrink. If a sea cucumber is starving, instead of rolling over dead it just eats itself, gradually becoming smaller and smaller.

  • They’re unsung heroes of the seagrass

    Psychropotes. Photo © NOAA Photo Library / Wikimedia Commons

    A sea cucumber’s daily life is about as boring as their vegetable namesakes, but it’s also important to ocean ecosystems. As the scoot around the seafloor, eating and pooping, sea cucumbers help distribute nutrients and remove excess organic matter from the sediment and water. Research shows that the presence of sea cucumbers leads to more productive seagrass beds.

    And by disollving calcium carbonate and pooing it back out into the water, they help provide the raw materials that corals need to grow their exoskeletons. Higher levels of calcium carbonate also increases the alkalinity of the water, which acts as a buffer against localized acidification.

    They might not be a keystone species, but for a little blob of mobile intestines, sea cucumbers do a pretty good job of making themselves useful.

  • They’re at risk of extinction

    Photo © Jerry Kirkhart / Wikimedia Commons

    I don’t think you’ll argue with me when I say that sea cucumbers have the culinary appeal of a boiled kitchen sponge. And yet populations around the globe are collapsing because sea cucumbers are considered a delicacy in some Asian cultures.

    Hauled out of the water, sea cucumbers are gutted, packed with salt, boiled, dried, boiled again, dried again, and then shipped off to markets in Hong Kong and Singapore. There they sell for exorbitant prices to consumers, who — wait for it — boil them again and serve them as a high-status meal for special occasions.

    The Nature Conservancy is working with Papua New Guinea communities to set up sustainable management of their sea cucumber fisheries, in the hopes of protecting these creatures and securing stable income for rural communities. 

Justine E. Hausheer

Justine E. Hausheer is an award-winning science writer for The Nature Conservancy, covering the innovative research conducted by the Conservancy’s scientists in the Asia Pacific region. She has a degree from Princeton University and a master's in Science, Health, and Environmental Reporting from New York University. Justine's favorite stories take her into pristine forests, desolate deserts, or far-flung islands to report on field research as it's happening. When not writing, you can find her traipsing after birds, attempting to fish, and exploring the wild places around her home in Brisbane, Australia. More from Justine

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  1. Wow….that is so interesting! I did not know this. This was fascinating. Thanks.

  2. Well done, Justine!! My kids will be as fascinated as I when I read this to them!

  3. Having grown up eating them when they were not fancy cuisine, I attest they are delicious. The Papua work is a small but important step in protecting them.

  4. This is so fascinating. We saw so many of them (huge too!) when we honeymooned in the Seychelles! I too think sea cucumbers are fascinating (thanks to my biology teacher introducing me to them many years ago.) What a nifty and informational post! Cheers!

  5. Hilarious and awesome! We can always turn to Mother Nature to come up with some amazing creature.
    Thanks so much for the story.

  6. What a brilliant article. I expected to read just a few snippets about what I thought was a vegetable, but found the whole post compelling reading. Well done Justine.

  7. Very good writing, I laughed my face off in the Vietnamese soup restaurant, I will need to go retrieve it later

  8. Hello, my mane is Dot. I have seen a sea creature on The Blue Planet and would love to know what it is. It’s whitish, dome shaped has a lot of short legs like paws and are frilly on the edges and the legs all move independently. It moves across the sea floor. Can you tell me what it is, and if you can send a photo, it is intriguing me. Thank you Dot.

  9. I had no idea! Thank you for teaching us about these, I can see why you are fascinated. Sounds like the Florida Keys shoild also invest in sea cucumber futures.

  10. […] Sea cucumbers are the humble vacuum cleaners of the sea, quietly tidying the environment as they creep across the sea floor on hundreds of tube feet. I consult for projects growing sea cucumbers, for the lucrative Chinese market; so I have studied them for many years and find them fascinating – and decidedly weird. […]

  11. I touched a sea cucumber at a Sea Life Aquarium Centre. It was very boring really, there was a young lady who had a shallow pool and I was looking at the things that were inside. One was the sea cucumber and she told me that I could touch it.
    It felt cold and lifeless really, a bit like a real cucumber but smaller and underwater.
    I didn’t know anything about it then, I am sure that she probably told me some things but they didn’t make the same impression on me as your funny article!
    It’s sad that they along with nearly every other species in our world is threatened with extinction, it makes me sick, mad and sad. But you made me smile so thanks for that.