Sea Sponges Use ‘Optical Fibers’ to Transmit Light

Why Sea Sponges Beam Light Deep Inside Their Bodies

An orange puffball sponge Tethya aurantia – Photo credit: Steve Lonhart / SIMoN NOAA.

Sponges grow large by feeding on carbon, nitrogen and other metabolites, which are provided by smaller organisms including algae and cyanobacteria. However, algae and similar organisms require light to survive.

So, how do they survive deep inside the sponges without any apparent access to light?

That mystery now seems to have been solved. A team of researchers at the University of Stuttgart have discovered that sponges use glass-rod structures, like optical fibers, called spicules to beam light deep inside their bodies.

The researchers placed light sensitive paper deep inside living sponges of species Tethya aurantium in a darkened seawater tank and then shone light on the surface of the sponges. When they recovered the  paper, they discovered dark spots corresponding exactly to the end of each spicule, where the light had exited.

The researchers tested another sponge that grew without the specules, in a control experiment. They confirmed that the light did not transmit without the spicules.

Porifera: Skeletons

Sponges, like all animals, possess some sort of a skeleton that gives their bodies shape.

As a whole, poriferans have diverse skeletal elements including calcareous laminae, organic filaments, and siliceous and calcareous spicules.

The skeletons of each of the major poriferan groups are distinctive and have been used to reconstruct their evolutionary relationships.

Spicules come in an array of beautiful shapes, as seen in the SEM images to the right.

These images were obtained using UCMP’s Environmental Scanning Electron Microscope.

Spicules are often categorized by size, the larger being megascleres and the smaller microscleres.

Some spicules are formed of the mineralized substances calcium carbonate and silica, while others are made of an organic substance called spongin.

Spongin skeletons were and are used as scrubbers in bathtubs, though they are fairly expensive. The ubiquitous bathtub accessory called a lufa is NOT a sponge, but a plant. The mineralized forms are considerably more hard and are not as frequently used for commercial purposes. Image and Caption: UCMP.