Dive Dry with Dr. Bill

#190: The Crevice Sea Cucumber

Mom and Dad raised my sisters and me with good manners. We always ate with a knife, fork and spoon unless we were lucky enough to have something we could eat with our hands like corn-on-the-cob or Dad's specialty, hamburgers on the barbecue. Of course I always handed my yucky peas to one of my sisters under the table. Mom expected any guests at our dinner table to behave properly as well. During the course of my two thousand plus dives, I've encountered many critters Mom would never tolerate at the dinner table. Today's column is about one that is very common in our waters, the crevice sea cucumber.

You may remember my previous column on the warty sea cucumber. That species was invited to the dinner table in many Asian households where it, and other members of its group, are not guests but served as part of the meal. In those cultures they are valued as aphrodisiacs. The Japanese refer to them as namako. I've never heard of anyone eating the crevice dwelling species for that purpose. Hmmm, perhaps I should try making my next batch of Thai green curry with the longitudinal muscles from this species. I'll have to invite one of my lovely dive buddies over to dinner for two at my house.

So, why wouldn't Mom invite the crevice sea cucumber to dinner? Simple. It eats with its "hands," or to be scientifically accurate with its tentacles. The species I've observed here appears to have nine feeding tentacles which it extends out from the crevice its body is tucked into. This way the sea cucumber can feed without risking becoming an aphrodisiac... er food... for a horny... er hungry... fish or invertebrate. The soft body is protected by the surrounding rock and only the feeding tentacles are at risk... of being fed on themselves. Come to think of it, 10 would be a more normal number... perhaps this individual did lose one to a hungry crab or fish!

The crevice sea cucumber seems to have perfected a skill I used in playing hide and seek with my childhood friends. I would try to squeeze into the narrowest spaces... back then I could! These critters twist, turn, bend and flatten their bodies to fit into very narrow crevices in the rocks. This strategy leaves their soft bodies well protected against potential predators. The only parts that are exposed are the feeding tentacles, and these can be withdrawn should an inquisitive fish begin nipping at them.

The sea cucumber waits for organic matter or small marine life to fall onto the sticky tentacles. It then bends the tentacle over to the "mouth" and sticks it down its throat. The sea cucumber then withdraws the feeding tentacle, undoubtedly slurping it clean, and then rams another food-bearing tentacle into the mouth. Several times I've observed and filmed these sea cucumbers to try to determine if there is any pattern to what order the tentacles are "swallowed." Despite speeding up the motion (they are very slow feeders, Mom would approve of that) I could detect no order in the process.

Other members of this group, like the warty sea cucumber, live exposed on the sandy or rocky bottom. They feed in a different manner, ingesting sand or detritus and extracting the organic matter including bacteria and other small organisms from it. They then expel the nicely "cleaned" sand. Mom might welcome them... at least they feed with their mouths and not their "hands..." er, tentacles! A commercial fishery for these sea cucumbers is expanding to serve Asian markets, just as the sea urchin fishery did.

Back in the late 1960's I was introduced to crevice sea cucumbers by Dr. Bob Given who was then at the USC Marine Science Center. Bob was a big help to me when I started my career here on the island. He has also given a lot to the island through his position as a Benefactor Member of the Conservancy. I'd like to take this opportunity to extend my best wishes to him for a speedy recovery.

© 2006 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles" or "Giant Sea Bass" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Crevice sea cucumbers lined up along crevice in a boulder; crevice cucumber showing
all nine feeding tentacles; feeding using top tentacle (L) and bottom tentacle (R).

This document maintained by Dr. Bill Bushing.
Material and images © 2006 Star Thrower Educational Multimedia