Most drugs in use today come from nature. Aspirin, for example, was first isolated from the willow tree. Penicillin was discovered from common bread mold. To date, the majority of drugs derived from natural sources come from land-dwelling organisms. However, as demand grows for discovery of novel industrial enzymes and new medicines, researchers are increasingly looking towards the ocean. Systematic searches for new drugs have shown that marine invertebrates produce more antibiotic, anti-cancer, and anti-inflammatory substances than any group of terrestrial organisms. Particularly promising invertebrate groups include sponges, tunicates, ascidians, bryozoans, octocorals, and some molluscs, annelids, and echinoderms.
Some chemicals produced by marine animals that may be useful in treating human diseases include:
A striking feature of this list is that all of the organisms (except the cone snail) are sessile (non-moving) invertebrates. To date, this has been true of most marine invertebrates that produce pharmacologically active substances. Several reasons have been suggested to explain why sessile marine animals are particularly productive of potent chemicals. One possibility is that they use these chemicals to repel predators, because they can't move to escape. Another possibility is that since many of these species are filter feeders, they may use powerful chemicals to repel parasites or as antibiotics against disease-causing organisms.
Competition for space may explain why some of these invertebrates produce anti-cancer agents. If two species are competing for the same piece of bottom space, it would be helpful to produce a substance that would attack rapidly dividing cells of the competing organism. Since cancer cells often divide more rapidly than normal cells, the same substance might have anti-cancer properties.