Sponges with skeletons made up primarily of glass use a complex array of engineering tricks to overcome the brittleness of their building material and withstand the rigors of life attached to the seafloor.

In a paper published Friday in the journal Science, researchers describe the elaborate structures that the sponges build.

"The resultant structure might be regarded as a textbook example of engineering," said Joanna Aizenberg, a researcher at Bell Laboratories/Lucent Technologies in Murray Hill, N.J., and lead author of the study. "The complexity of this glass skeleton is an example of nature's ability to improve inherently poor building materials."

Aizenberg and her team catalogued seven levels of structure in deep-sea, sediment-dwelling sponges from the genus Euplectalla that represent "major fundamental construction strategies such as laminated structures, fiber-reinforced composites, bundled beams and diagonally reinforced square-grid cells."

The scientists have been studying the glass sponges for several years, their interest initially spurred by the ability of certain fibers in the sponges to conduct light as well or better than the best man-made fiber-optic cables.

Aizenberg noted several years ago that the sponge fibers are actually stronger and more resistant to breakage than man-made optical cables, in part because they're assembled in the cool temperatures at the bottom of the ocean.

Every structural level contributes to the mechanical stability and toughness of the resulting design of the sponges, which resemble glass cages that often house a pair of breeding shrimp inside them, the researchers report in the new study.

In fact, Aizenberg suggests that the sponges transmit the light of bioluminescent shrimp hiding in and around them at murky depths of 1,500 to more than 3,000 feet. That helps the shrimp attract food, while in turn the sponges collect waste and leftovers from the shrimp.

The fiber structures start with individual needle-like glass filaments composed of alternating layers of glass and carbon-based glue. These make up the basic structure of each closed, cylindrical cage.

Those filaments are bundled together to form beams that are stronger still. The beams are arranged horizontally and vertically to create a latticework of squares that form the cage.

Diagonal silica beams reinforce every other square, and multiple layers of glass cement strengthen the beam intersections. Then, the glass cages are wrapped with spiraling surface ridges that keep them from being squeezed like an empty soda can.

In addition, the sponges use special fibers to anchor them to the soft sediments of the seafloor. But the anchors are attached to the rigid cages with particularly flexible struts that allow the sponge to swing freely back and forth in strong currents.

On the Net: www.sciencemag.org

(Contact Lee Bowman at BowmanL(at)SHNS.com. Distributed by Scripps Howard News Service, http://www.shns.com)