Mar 13, 2008: Sea Cucumbers. Even wierder than moon snails.

Here are some facts you probably didn't know about sea cucumbers:

1. They breathe through their anus.
2. They have a compound in their skin called catch collagen that allows them to liquefy or melt on command. They use this skill to escape into small, safe crevices to evade predators.
3. They have an escalating response to stress. If you poke them with a stick, or hold them in your hand, they'll probably goopify. If you continue to mess with them they may puke their guts out, or eviscerate themselves. If you really, really bother a sea cucumber, it will inhale a bunch of water through its anus and then rupture its hind end to expel a bunch of noxious chemicals. When this happens in an aquarium it can kill all the tank mates-- something aquarium keepers call a "cuke nuke."

Step 1: Goopification

Sea cucumbers, together with sea stars and sea urchins, are echinoderms. There are 900 known species of cucumber; the one pictured here is Parastichopus californicus, or the California Sea Cucumber. It's supposed to be nocturnal, but we found two cucumbers passing a nuit blanche on a low tide in February. When we found the first one, Dave, an oyster picker who's worked on the Hama Hama tideflats for over a decade, said it was the first cucumber he'd ever seen on the beach. So we felt really good about finding another one a couple hundred yards away from the first.

Sea cucumbers are very edible. The 5 longitudinal muscles in the cucumber are considered a delicacy. But they were over harvested a couple of decades ago in the Canal, and are only now making a comeback. So I'm not going to post any sea cucumber recipes. They eat passing plankton and plant and animal detritus off the sea floor, and are important ecologically.

Don't mess with the cucumber.

What Sea Cucumbers Tell Us About the Health of the Beach

Finding two cucumbers on the same low tide, a couple hundred yards apart, felt like more than luck. Sea cucumbers are generally considered indicator species, their presence (or absence) reflects the overall health of the benthic environment they live in. A beach with a recovering cucumber population is, in most cases, a beach where the water quality, sediment, and food web are trending in the right direction. For us, spotting them on the Hama Hama tideflats, the same tideflats where our oysters grow, felt like good news. Not proof of anything, exactly, but a sign worth noting. Dave has been walking this beach for over a decade, and he'd never seen one before. Two in an afternoon felt like the beach was trying to tell us something.

Final Thoughts

Sea cucumbers are not the most glamorous residents of the Hama Hama tideflats. They don't have the visual drama of a sea star or the culinary cachet of a Dungeness crab. But they're doing important work down there, filtering detritus, aerating sediment, and, apparently, breathing through their anuses. Finding two of them on a February low tide, in a canal where they'd been largely absent for decades, was one of those quiet moments that reminds us why we pay attention to what's living on our beach. The tideflats are an ecosystem, not just a farm, and the sea cucumbers, goopy, stress-puking, self-rupturing as they are, are part of what makes it work. We're glad they're back. We're going to leave them alone. 

Frequently Asked Questions

Are sea cucumbers dangerous to humans?

Not in any direct way, no. They won't bite, sting, or chase you down the beach. That said, the chemicals expelled during a cuke nuke, the stress response where a cucumber ruptures its hind end to release noxious compounds, can be harmful to other marine life in an enclosed space. In an aquarium, it can wipe out an entire tank. On an open tide flat, the risk to you personally is low, but we'd still recommend not picking them up or poking them with sticks. They're recovering from decades of overharvesting, and they'd appreciate being left to it.

Can you eat sea cucumbers?

Technically, yes, the five longitudinal muscles inside a sea cucumber are considered a delicacy in several parts of the world, particularly in East and Southeast Asian cuisines where they're known as trepang or bêche-de-mer. The texture is gelatinous, and the flavor is mild. That said, we're not posting any sea cucumber recipes here, and we'd encourage you not to harvest them from Hood Canal. They were severely overharvested in the Canal a couple of decades ago and are only now making a comeback. Let them recover first. There will be time for recipes later.

What's the difference between a sea cucumber and a sea slug?

They look vaguely similar if you squint, but they're not closely related. Sea cucumbers are echinoderms, the same family as sea stars and sea urchins, while sea slugs (nudibranchs) are mollusks, more closely related to snails and clams. The easiest tell: sea cucumbers are generally larger, rounder, and more sausage-shaped, while nudibranchs tend to be flatter, more colorful, and frankly weirder-looking. Both are worth finding on a low tide; neither should be poked.

Why are sea cucumbers nocturnal, and why were these ones out during the day?

Parastichopus californicus, the California Sea Cucumber, the species we found, is generally nocturnal, which made finding two of them on a February low tide during daylight hours a little unusual. Our best guess is that the combination of an exceptionally low tide and cool winter water temperatures drew them out, or at least caught them mid-wander before they could get back under cover. We don't know for certain. Dave, who's been picking oysters on this beach for over a decade, had never seen one before that morning, so we're not going to pretend we have a definitive answer. Sometimes the beach surprises you.

How do sea cucumbers fit into the tideflat ecosystem?

They're doing more than you might expect for something that looks like an overgrown pickle. Sea cucumbers are deposit feeders, they move along the sea floor ingesting sediment, extracting nutrients from passing plankton and organic detritus, and excreting cleaner sediment behind them. In practical terms, they aerate the substrate, recycle nutrients, and help maintain the kind of benthic environment that other species, including bivalves like our oysters and clams, depend on. Their recovery in Hood Canal is genuinely good news for the broader ecosystem, which is part of why we'd rather watch them than eat them, at least for now.