Ocean Watch
By Susan Scott
Monday, March 16, 1998
A reader recently sent me a newspaper clipping (source unknown) that said, "Break a sponge into thousands of pieces. Scatter them in a tank. Next day, they'll be reformed in the exact shape of the original sponge." Sponge’s way of cloning
requires only seawater"I will be grateful," wrote the reader, "if you can tell me how it is possible that such a thing can happen."
Such a thing can happen because sponge biology is like the biology on "The X-Files": weird. I mean, if Sojourner had found water on Mars, there probably would have been sponges in it.
On this planet, sponges rank one notch above single-celled animals, such as amoebas, on the evolutionary scale. A sponge has no nervous system and no muscles. This means no stomach, no eyes, no pain, no movement.
In spite of this, sponges manage to do some remarkable things, beginning with building unusual skeletons.
Some sponges keep their shape by forming spicules, tiny rods that brace up the sponge's cells. Spicules are made either of calcium carbonate, like the skeletons of stony corals, or of silica, a
glasslike material that can stick into, and hurt, human skin.
Other kinds of sponges stand up with the support of tough, rubbery fibers called spongin.
Sponges containing this soft type of skeleton are the bath and cleaning sponges familiar to us all.
What do sponge cells do in the midst of all this supportive scaffolding? Most of them line up to form a network of canals covered with tiny, beating hairs. These hairs move water into the sponge through pores at the surface, and out through holes.
One of the things that comes into a sponge on these self-made currents is food in the form of plankton: bacteria, microscopic seaweed, one-celled animals, and sex cells released by plants and other animals.
Although some sponges grow to immense size, reaching more than six feet in diameter, they can still eat only food no larger than what one cell can swallow at a time. That's one disadvantage of not having a stomach.
Another item sucked in by the sponge's continual current is sperm from other sponges.
Most sponges are hermaphrodites, each individual bearing both eggs and sperm. Sperm gets shot out through one of the sponge's openings, then inhaled by another and transferred to its eggs.
There, the fertilized eggs remain protected and fed. When mature, the youngsters get ejected, swimming until they find suitable sites to settle down and become full-fledged sponges.
But that's not the only way sponges reproduce, and herein lies the answer to my reader's question.
If you press a sponge through a fine silk cloth, the sponge's cells fall out singly. If these cells are in a dish of seawater, they begin creeping around the bottom. If one runs into another, the two stick together and continue crawling. Eventually, tiny masses of cells form which then organize themselves into new sponges.
So.
It's true that when a sponge is broken up into thousands of pieces, each piece will become a tiny new sponge exactly like the original, and exactly like each other. Such asexual reproduction is called cloning.
Other sponge facts:
Hawaii hosts about 63 species of sponges, ranging from tide pools to depths of over 300 feet. Twenty-four of those species live only in Hawaiian waters.
Marine science writer Susan Scott's Ocean Watch column
appears Mondays in the Star-Bulletin. Contact her at honu@aloha.net.
