Six easy lessons in: Sponges

While not the most attractive of ocean creatures, sea sponges have both a history and a future in scientific research. Dr Michael Ellwood from the Research School of Earth Sciences takes us through the basics of these simple animals, assisted by PhD students Jill Sutton and Andrea De Leon.

Are sponges animals or plants?

Despite looking like a plant growing from the ocean floor, sea sponges do not photosynthesise, but rather consume organic matter from the ocean around them, which makes them an animal. Sponges are classified into three species based on their skeleton, whether its made from glass (silicon), calcium carbonate or organic matter. In the Research School of Earth Sciences, research is focused specifically on silicon skeleton sponges that can be found in fresh or saltwater at any depth, anywhere in the world.

How long have these multi-cellular organisms been around?

Sponges evolved somewhere between 540 and 600 million years ago, and that’s just the ones we know about. “One of the difficult aspects with dating these organisms is that is you can only date the ones that leave fossil skeletons,” Ellwood says. “And plenty of species, particularly the organic ones, don’t leave a fossil record so we don’t know for sure if they were there.” Here in Australia we have existing species dating back more than 35 million years.

Some sponges still retain exactly the same morphology as they did hundreds of thousands of years ago because there haven’t been any pressures on them to change, with a simplistic cellular structure and glass skeleton that acts as a deterrent for predators.

Would a sponge survive being put through a blender?

The simplistic structure of sponges means that each cell is autonomous and is able to perform all the cellular functions common to the sponge. “In humans, once you’ve laid down a liver cell, that’s all it knows how to be. But in a sponge, each cell knows how to do everything that a sponge does,” Ellwood says.

Thanks to the autonomy of the cells, you can cut a single sponge into three, eight or 20 pieces and have three, eight or 20 smaller sponges in its place. The researchers have even heard of experiments that have seen sponges added to blenders, only to have the cells join together in a new formation to make a new sponge.