Sponges are common and important inhabitants on reefs, as well as elsewhere in oceans. They play an important role in maintaining water quality, as they filter large amounts of water, from several to many times their own body volume, every day, cleaning the water from small particles and bacteria. Sponges are primitive animals, and, as such, they should in principle be very nutritious, and being sedentary, should have major problems avoiding being eaten by predators. That doesn´t seem to deter sponges in any major way, as they inhabit the reef and other shallow waters we divers visit. So how do the sponges survive the dense array of predators living in the marine environment?
Time is the key to the answer. Sponges have been around for a very long time. They are more than 500 000 000 years old, which leaves a long time for evolution to work its ways. Being sedentary, the only possible defense has been to use chemical substances. And that is exactly what has happened. Sponges are full of distasteful and toxic substances of many different types, making it very hard for any animals to crack the code and use them for food. Some nudibranchs, some angelfish and actually a turtle, the hawksbill, forage on sponges, but these predators on sponges seldom occur at high densities and might even have to change sponges during a foraging bout in order to not exceed problematic levels of defense substances.
Defense compounds as those in sponges are per definition biologically active compounds. That is what the biochemical industry is looking for in labs and in nature all over the world. Given their long history of evolution of defense compounds, sponges has been at the center of interest researchers wanting to develop new drugs. There are already sponge-based substances on the market, and more will certainly be developed in the near future. So, in the future, sponges could hold the solution to quite a number of problems we humans face. Give that a thought the next time you pass by one of those mostly overlooked sponges!