Sea cucumber plays cruise ship to clever brittle star

Sea star
© David Fleetham via bioGraphic

Riding along from reef to reef, brittle stars get all kinds of perks when teaming up with sea cucumbers.

While the scene above – photographed by David Fleetham – may look like something out of a sci-fi flick, it's actually just business as usual at the bottom of the sea. In this case, it's a Savigny's brittle star (Ophiactis savignyi) taking a ride on a leopard sea cucumber (Bohadschia argus). Because, why not?

At 10 times the size of its tiny stowaway, sea cucumbers often play cruise ship for brittle stars. Both echinoderms (the fabulous phylum that includes starfish, sea urchins, brittle stars, and sea cucumbers) share many of the same habitats and thus frequently meet up. As bioGraphic explains, scientists are still figuring out the benefits of such arrangements; however, Christopher Mah, a marine biologist at the Smithsonian Institution says research has unraveled some of the mystery.

Explanations include an obvious one: simply seeking the protection that a big sea cucumber affords. Sea cucumbers have a whole array of fancy defense mechanisms that keep many a predator at bay; think foul-tasting chemicals, fleshy protrusions, and the ability to "shoot a web of sticky strings called Cuvierian tubules out of their anuses as a deterrent to predatory crabs and mollusks" ... I'd stay away too.

Brittle stars are also treated to a veritable buffet as their ride sifts through sediment stirring up snacks that the stars can grab with their arms. And not to mention that hopping on a sea cucumber helps the brittle stars to get from one coral reef to another more expeditiously than on their own.

Sea cucumberWikimedia Commons/CC BY 2.0

While the brittle star's perks are notable, this is really a story about the mighty sea cucumber, who plays host to a whole tiny ecosystem of creatures, notes bioGraphic, "including clams that take up residence in cucumber throats, fish and crabs that colonize their anuses, and worms and snails that drink their bodily fluids."

Nobody said being a sea cucumber was easy. But while a tube of a creature that rambles about the ocean floor may not got that much love from the world, it's clearly a local hero at home, providing benefits to an entire community ... including tiny brittle stars that hop on for a ride.

To see more of David Fleetham's otherwoldly underwater photography, visit his site here. For more intriguing science and nature stories, visit bioGraphic.

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