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Glass Sponges

Animal, vegetable or mineral? Glass sponges do not have eyes or a mouth or stomach, and so might be mistaken for a plant or a rock, but they are in fact living, breathing animals. Adult glass sponges are “sessile”, meaning they do not move. Their bodies have thousands of tiny holes, or pores, through which water constantly flows. They absorb all the food, oxygen, and silica they need straight from the water that surrounds them. They get rid of their waste straight back into the water, which they pump out through their tube-shaped “oscula” with the help of the surrounding water current.

To reproduce, glass sponges release their ‘babies’ into the water as tiny swimming larvae that are carried by currents. If they land on a suitable surface, for example another glass sponge or a rock, they will transform and grow into a small replica of the adult.

Glass sponges form a massive skeleton for structural support. The skeleton is made of silica, which the sponge forms into delicate needle-like structures called “spicules”. Clev­erly, glass sponges also fuse the points on the spicules together, much like scaffold­ing, to create a lattice-like skeleton. Their intricate skeleton is further strengthened as they grow and touch other glass sponges gaining support from each other and creating the three- dimensional framework, which is called a reef. 3 These skeletons remain intact long after the sponge itself dies, which has resulted in some reefs reaching heights of up to 20 m 4 – the height of a six-storey building.

The three species of glass sponges in Hecate Strait that are able to build reefs require an amazing amount of silica. If the reefs grow only one centimetre per year, it has been estimated by scientists that it would take 57,000 5,6 tonnes of silica. This is the equivalent of 1,000 railway cars full of silica a year!

To read more about these fascinating creatures, go HERE.