Sponges are important because of their roles in recycling nutrients and the part they play in the coral reef life cycle. For instance, sponges break down complex organic material into food for other things living on the coral reefs.
Much of the organic material that algae and coral produce can't be used in its current form by other inhabitants of the coral reef because of its complexity. This is where the sponges prove useful. They can take this complex material and turn it in to something a little simpler. According to the Coral Science Organization, much of their diet consists of dissolved organic carbon. Sponges also help to lower nitrogen levels in the water and keep the ecosystem clean because bacteria found in the sponge turns this nitrogen into forms of food.
Although sponges are multi-cellular animals, they also have one of the simplest structures. Instead of soft tissues and organs, sponges have pores that bring water and nutrients into them. This water is then expelled through an opening in the top of the sponge called the osculum. Sponges attach themselves to rock, and they range widely in both color and size. Some species of sponges also ingest very small crustaceans.