From touch tank to no-touchy
When Jake, Brad and I used to visit the Monterey Bay Aquarium, we’d thrill at the chance to hold a sea cucumber in our hands. We would intentionally visit during hours when we knew the touch tank wouldn’t be busy. With an aquarium volunteer looking on, we’d sink our hands into the tank and scoop out the bright orange sea creature, holding him just above the water and feeling the scrunch and release of his muscles as he tried to crawl away.
Here on Kwajalein, sea cucumbers abundantly dot the swimming area and the reef, but we’re pretty grossed out by them. Nora won’t go near one – Jake has to clear them from the sides of the snorkeling pools before she’ll get in. She’s even made a warning sign to keep people from being confused between sea cucumbers and a loaf of bread. I’ve no idea why she thought that might be necessary since we usually see a knobby, purplish-black variety where we swim, and I’ve never seen a knobby black loaf of bread, but nevertheless, we’ve all been warned.
These slow-moving cucumber-shaped – hence the name – animals are echinoderms, cousins to the starfish, the sea urchin and the sand dollar. They can be found everywhere sea water flows around the globe. With skin made of collagen and jelly-like internal organs, sea cucumbers can nearly liquify their bodies in order to fit into tiny spaces or escape from predators. But when they feel stressed or threatened, the collagen fibers – fibriles – under a sea cucumber’s skin lock together, creating a tough, leathery exterior that protects the slow mover from fast predators.
A sea cucumber’s life is all about eating. Brainless and acting instinctively to find food, the animal’s front tentacles reach out along the ocean floor or the reef like a dime-machine sticky hand to scavenge algae, other tiny animals or even waste, breaking it all down into smaller pieces before excreting fine sand, similar to what earthworms do in garden soil. This crucially important reef waste-cleaning function earns cucumbers the nickname “reef vacuum.” When Jake and I snorkel, we frequently observe piles of sea cucumber poop mounded like sandy beads on the ocean floor or reef, like earthworm castings on a healthy lawn.
How to defend yourself when you can’t really move
When my Mom and Dad were visiting in October, I dared my mom to hold a small sea cucumber while we were walking on the reef. She plucked one of the critters from a pool in the rock, and its defense mechanisms kicked in: first, stiff skin and a long water squirt (as Brad and Nora shouted, “Eeeew, it’s peeing!”). Laughing, Mom put it back down, but if she’d kept it in her hands, it might have expelled its internal organs to further defend itself from her clutches. The innards are quickly regenerated when the cucumber is back under the water, an adaptation I’m sure they find handy (even though they don’t have hands).
While over 1700 hundred sea cucumber species cover the globe, the sea cucumbers we see here on Kwaj most commonly are black. Or when the sun shines, they look like they could be that color of purple that is so dark, it looks black. In warm tide pools, they sink into the rock and grit, covering their skin with a protective layer of sand. In September, while we were searching tide pools for brittle sea stars, another type of echinoderm, Jake flipped over a rock and found the underside crowded with young sea cucumbers, some only an inch long. It reminded me of when Brad loved to turn over the bricks lining our front garden to look for slugs. I had the same “that’s so gross but I can’t look away because it’s so cool” reaction when Jake lifted the rock so I could snap a photo. To reproduce, sea cucumbers spray eggs and sperm into the water, relying on large quantities of reproductive material and the current to carry on their genetic line. So at some point, a couple of sea cucumbers sprayed their reproductive cells into the ocean current, and enough of the cells met up and lodged in a chunk of that reef to allow me to observe a lineup of shiny purple baby sea cucumbers.
In 2013, three marine biologists from the University of Guam and the University of Queensland conducted a six-day survey of sea cucumbers on Chuuk, a Micronesian island about 1800 miles from Kwaj. In less than a week, they found 34 sea cucumber species at 11 sites around the island, including several species that had never been described before. In total, the scientists say, more than 60 species of sea cucumber are likely to call the waters around Chuuk home. In distance, we’re a long way from Chuuk, but the surrounding waters share many of the same characteristics. I’m not making too much of a leap to say that I might be able find 50-60 different kinds of sea cucumbers around Kwaj, even though I can only think of two or three different kinds I’ve ever noticed before when I’ve been snorkeling or scuba diving.
My fuzzy memory regarding what types and kinds of sea cucumbers I may have seen just demonstrates that since they’re so commonly found, and also since they’re ugly and a little gross, sea cucumbers are easy to overlook or just ignore. I’ve probably stopped noticing them entirely unless I see an especially strange variety, such as the 3-foot long creature I saw with a group of friends while we were snorkeling in a tide pool. It looked a lot like this guy. I snorkeled right over the long, thin, brown-and-tan striped animal at first because I thought it was a stick. But then I saw the tentacles at the other end, so I stopped to appreciate the animal as it ate, reaching feathery tentacles forward, bunching muscles along the length of its body, and slowly maneuvering across the sandy floor of the tide pool. One friend and I agreed that the creature was repellent, almost revolting, difficult to look at. But we kept putting our faces back in the water to examine it a little more. The surprise of its anatomy – long enough for a snake, but not a snake at all – and the bewildering way it seemed to purposefully suction food particles from the sand planted a sense of astonishment and wonder next to a feeling of revulsion in my gut. Not bad for a lumpy, pickled-looking, brainless, waste-eating, bottom-feeding, reef cleaning sea cucumber.