This is a difficult thing for a coral biologist to say, but the top spot in my All-time Favourite Sessile Marine Creatures list has just been taken by a sponge. The Venus’ Flower Basket sponge dwells in the deep sea sediments of the Western Pacific and is probably the only marine creature to have appeal to structural engineers, architects, biologists and wedding guests alike.
Venus' flower basket. Copyright Andrew Just
The structural properties of the biosilicate skeleton of this sponge (scientific name Euplectella aspergillum) are of interest due to Venus’ flower basket. Copyright Andrew Justthe immense strength that it confers to the sponge, allowing it to withstand the enormous pressure in the deep ocean. Due to its microlayer structure, sponge glass is not brittle, unlike man-made glass. The glass fibres, which are made up of concentric layers, are bundled together and bound by an organic cement to form the cage-like skeleton of the sponge. The horizontal and vertical arrangement of the fibre bundles further strengthens the skeleton, protecting the structure from torsion or collapse. Curved ridges on the outside of the skeleton provide yet further protection from collapse, and overall the sponge skeleton incorporates seven levels of structural hierarchy, from the nano- to macro-scale. These hierarchies correspond to fundamental construction principles commonly applied by civil engineers in, for example, high-rise building construction.
Not only are the glass fibres remarkably strong, they also possess an important additional property that is of interest to nanotechnologists. Current production techniques for optical fibres require high temperatures and the resultant fibres are brittle. The hair-like fibres that attach the sponge to the ocean floor have excellent optical properties but are much less brittle and have been produced at low temperature. If these fibres could be recreated in a laboratory, more efficient and lower cost solar cells could be developed, with obvious benefits to mankind. Significant advancements in architecture and engineering due to the discovery of the remarkable properties of this sponge also seem to be inevitable.
Venus' flower basket. Copyright Andrew Just
Another appealing feature of the sponge is the close relationship it forms with a pair of shrimp. Tiny shrimp larvae are able to penetrate holes in the sponge skeleton and soon become too large to escape. The male and female shrimp live their entire lives in symbiosis within this glassy prison, providing benefit to sponge by the keeping the inside of the basket clean and in return are able to feed on food trapped by it. Miniscule offspring are able to exit through the holes and find sponge homes of their own. The symbolism of this relationship is such that in some asian cultures Euplectella is given as a wedding gift.
Once you are aware of the amazing optical and structural properties it possesses, looking at the seemingly-fragile skeleton of a Venus’ Flower Basket under a microscope becomes a somewhat humbling experience. It is truly one of nature’s most ingenious designs, beautiful and inspirational in its simplicity, and something from which we can learn a lot. Corals can’t even begin to compete.