Meet the sea cucumbers

A sea cucumber (Stichopus herrmanni). Retrieved from Wikipedia on 02/10/2022.

I was talking to my friend, wondering who I should write about this week. She told me I should write about sea cucumbers. I’ll admit, I was skeptical starting out. But friends, these animals are WILD.

Some simple facts to start with. There are over 1,000 species of sea cucumbers. They live on the sea floor, with the largest number of species being found in the Asia-Pacific region.

Sea cucumbers are echinoderms (Greek for ‘hedgehog skin’). Echinoderms are invertebrate marine animals and include starfish, brittle stars, and sea urchins. You know, those usually scaly / prickly creatures with radial symmetry. But unlike most other echinoderms, sea cucumbers don’t have scaly skin. They are basically a leathery tube with a mouth, a bunch of organs, and an anus.

Pretty simple creatures. “How could something so simple be remotely interesting,” you may be thinking. Well, buckle up. I’m about to tell you some wild things about sea cucumbers that will forever change your view of them. Warning: this is a poop- and butt-heavy post.

  • Males and females
    • We’ll start with the tame facts: sea cucumber reproduction. Most species of sea cucumbers are dioecious, which means there are separate male and female individuals. Instead of having sex as humans do, sea cucumbers use the surrounding water to their reproductive advantage – they just release sperm and eggs into the open ocean and hope they run into each other. The key to this strategy is to make a lot of gametes (sperm or eggs). The more you release, the more likely a sperm and egg will unite. In fact, one sea cucumber can produce thousands of gametes when the conditions are right.
  • Sand eaters
    • Sea cucumbers are detritivores, animals that eat dead organic material. They are scavengers that vacuum the ocean floor for algae, aquatic invertebrates, and waste particles hiding in the sand. Think of sea cucumbers as aquatic earthworms: as they eat the detritus, they break it down and recycle nutrients like nitrogen and calcium carbonate back into the ocean. They are recycling masters. A sea cucumber will expel 30.8 pounds of poop over the course of a year. That may not seem like much, but sea cucumbers only weigh 0.1 to 5 pounds, so in a year they poop more than six times their weight. Still doesn’t seem like much? Look at it this way: a human creates, on average, about 320 pounds of poop in a year (a little more than the weight of an adult panda). An average 150 pound person only poops twice their weight every year.
Edible sea cucumber (Holothuria edulis). Retrieved from Wikipedia on 02/10/2022.
  • Important shit
    • And this poop is important! Remember, sea cucumber poop contains calcium carbonate. This nutrient is essential for coral reefs to grow. Sea cucumber poop is also basic, which means that it lowers the acidity of the water surrounding coral reefs, further aiding in their growth. Sea cucumber poop is vital to a coral reef’s health and the overall ecosystem. Also remember just how much sea cucumbers are pooping a year. One study found three million sea cucumbers on a single reef released 64,000 metric tons of poop back into the ecosystem. That’s the weight of five Eiffel Towers. AKA, a lot of extremely important poop.
  • Butt breathing
    • In addition to excreting poop, sea cucumber butts are also vital for another important life process: breathing. The sea cucumber respiratory system is a pair of respiratory trees that are located just inside their anus. They “breathe” by drawing water through their anus, extracting the oxygen, and finally expelling the water. Oxygen then diffuses throughout the rest of the body.
  • Fish in the butt
    • In addition to pooping and breathing, sea cucumber butts are a refuge for some fish. You read that right: some species of fish live inside sea cucumber buttholes. The pearlfish finds sea cucumbers by their smell and the gentle currents created by their butt breathing. When the sea cucumber exhales, the pearlfish dives right in and makes its home in the cloaca of the sea cucumber. Pearlfish will get into the sea cucumber either head first or tail first, but 80% of the time they go in tail first. There is also usually only one pearlfish in a sea cucumber, but sometimes you get a male and a female. Because what better place to make babies than in someone else’s ass.
    • Now, this sea cucumber – pearlfish relationship is typically a commensal one, where one party (the pearlfish) benefits at no cost or benefit to the other (the sea cucumber). In this case, the pearlfish gets protection and the sea cucumber is totally unbothered. Usually. Some species of pearlfish (like Encheliophis) are actually parasitic. They live in the sea cucumber and EAT IT FROM THE INSIDE. Some sea cucumbers have evolved to protect themselves from these pearlfish and other parasites by evolving anal teeth. Just little hard teeth that protect the anal opening so no one can get in.
Look at that anus. Photo by Klaus Stiefel. Retrieved from Flickr on 02/10/2022.
  • Or clams in the throat
    • Let’s take a second and switch to the other end of the sea cucumber: the mouth. Some species of sea cucumbers have a clam parasite living in their esophagus. The esophagus is a pretty safe place for these clams, as it doesn’t have stomach enzymes and they don’t have to worry about evisceration (see below). And they get to pick out food bits as the sea cucumber vacuums up the ocean floor, at no apparent harm to their host. Don’t worry: as far as we know, no species of sea cucumber has both butt fish and throat clams.
  • Evisceration
    • Most predators avoid eating sea cucumbers because they are toxic. Some predators, however, have evolved to not be affected by sea cucumber toxins, and others are able to prey on sea cucumbers when better food is not available. So how can the sea cucumber protect itself when toxins are not enough? Easy: they eject their guts out. In a process called evisceration, sea cucumbers can literally expel their guts from their body when they are in danger.
    • Now, not all sea cucumbers eviscerate, and different types expel different organs and at different times of year. But the general process is the same: the ligaments attaching the organs to the body soften, the body wall softens, and muscles contract to spew out the guts. Predators are understandably not too pleased to be covered in toxic sea cucumber guts.
    • “But don’t they need their guts???” you may be asking. The answer is yes, but no worries! Sea cucumbers can regenerate the guts they lost. Regrowth time depends on the species and the organs lost, but it can apparently happen in as little as a week.
Stiff-footed sea cucumber. Photo by Jerry Kirkhart. Retrieved from Wikipedia on 02/10/2022.

I literally can’t stop thinking about sea cucumbers. I can’t believe I spent so much of my life thinking they were just dumb water pickles. They are so cool. Butt breathing! Butt fish! Guts squirting out! What more could you ask for in an animal?


Ocean Conservancy


Cool Green Science

Leave a Reply

%d bloggers like this: