Salt marshes were once considered examples of bottom-up regulation in which the ecosystem is determined by abiotic factors and nutrient availability. Ecologist Dr. Brian Silliman observed that the salt marsh was often covered with snails—what were they eating? Through a series of cage experiments, Dr. Silliman demonstrated that the snails control the amount of marsh grass by facilitating fungal infection. He also showed that blue crabs control the number of snails and therefore protect the marsh grass from overgrazing. This is an excellent example of confronting a long-held theory with data in order to improve and refine our understanding of the natural world.