When I visit a new region to dive, I am usually most interested in the common species of that region rather than the rare ones. Many divers of what I call the "collector mentality" look strictly for those rare species, especially if they want to add it to their photo collection. Fortunately rare species are often not very edible... or at least we don't know they are! It is the common species that often have the greatest impact on the ecosystems they live in... a matter of sheer numbers!
The subject of today's column is indeed a very common species in our waters, and its relatives are often very common in other regions of the world as well. They provide a vital ecological service just by feeding. I'm referring to the warty sea cucumber. These relatives of the starfish (now referred to as sea stars since they are not true fish) and sand dollar look superficially like a cucumber you'd dice and slice to put in your salad. In fact they are literally diced and sliced for another purpose which we will get into later since I am no culinary artist and this is not a column on food (at least not intentionally)!
Although they look nothing like a five-armed starfish (er, sea star), these sea cucumbers do have tube feet. The walls of their bodies are not hard like sand dollars or sea urchins, which possess calcium carbonate exoskeletons, but they do have small calcareous plates called spicules embedded in their skin. Yet scientists know they are related to them due to a few common characteristics that aren't very obvious to the untrained eye.
These sea cucumbers are benthic, that is they live on the bottom of the ocean. Here they use the "business end" of their cylindrical bodies to ingest bottom sediments like sand, pass it through their digestive tract to extract organic matter and small organisms from it, and then use the other "business end" to poop out cleaned sand. They are part of the ocean's recycling system, taking the organic wastes produced by other organisms and using them to build strong bodies more than 12 ways, since their food is probably much more nutritious than Wonder Bread. Not very appetizing to us, but very necessary in an environment filled with fish poopies and decaying bodies.
Sea cucumbers "breathe" in a pretty strange way. Instead of using gills like many marine animals, they pump water in and out of their anus. Inside, the rear portion of the gut has many branching extensions which serve to remove oxygen from the water and release carbon dioxide. While diving you can sit and watch that "business end" pumping water in and out of the body. Just make sure it isn't time to use it for its other function!
No known sea cucumber has evolved as a predator, so they are generally gentle, good-natured critters. In turn, despite its docile nature, most predators avoid the sea cucumber as a potential meal. Kelp bass, sand bass and some sea stars are known to occasionally dine on them. I have also observed sheep crabs feeding on them live, a form of sushi to the crab I assume. Recently I found a living cucumber with portions of its skin and muscle layer ripped off, possibly by another crab. These soft-bodied animals appear easy prey, but they do possess a few tricks to ward off predators. Some will eviscerate, essentially throwing their intestines out of the body for the fish to eat while they very slowly crawl away to regenerate their digestive tract. Our local species are able to crawl fast by looping their bodies like an inchworm if attacked. Others are known to release toxic chemicals if attacked, although this is usually only in tropical species.
Asian cultures are fond of eating sea cucumbers, and consider them an aphrodisiac. Perhaps this is because of the shape of the animal, and the fact that they can get quite rigid when handled. Hmmm... not that inscrutable. A close relative of our local cucumbers is favored in Japan where it is known as namako (other cultures call it beche de mer). I've been told by western males there that if they are dating a Japanese woman, her father will often take great delight in seeing if the suitor will eat such oriental delicacies. As my readers know, I'm quite partial to Asian women and would happily indulge in such fare if it will get me in good with their fathers... or will it, considering the effect they are believed to have on a human male's virility? Now that's inscrutable!
As for their own reproduction... most sea cucumbers have separate sexes (you know, buoys and gulls). The females often release many small eggs into the surrounding water where they are fertilized by sperm released by the nearby males. The embryos and resulting larvae drift in the water currents for a while before settling down. In some species the females produce a smaller number of larger eggs which may be fertilized and brooded internally rather than released as plankton.
One behavior I observe fairly often has eluded my understanding. Occasionally a sea cucumber will raise its oral end and literally sway back and forth in the air... er, water. I've referred to this as the cucumber's "dance" and have no idea what survival value it may have. Perhaps it is nothing more than responding to a different "drummer" heard only by their invertebrate senses, or perhaps they would have enjoyed the heyday of the "Big Band" era in Catalina's beautiful Casino Ballroom!
© 2005 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.
Warty sea cucumber resting on rock; performing its
through its anus; using the anus for a more "normal" purpose.
This document maintained by
Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia