In this video, ecologist Brian Silliman explains how he uses manipulative field experiments to study salt marsh ecosystems. His approach revealed that these systems are under top-down control from consumers and predators.

Salt marshes were once considered examples of bottom-up regulation in which population sizes are determined by abiotic factors and nutrient availability. Silliman observed that salt marsh grass was often covered with snails and wondered what the snails were eating. Through a series of cage experiments, Silliman demonstrated that the snails control the amount of marsh grass by facilitating a fungal infection that impedes the growth of the grass. He also showed that blue crabs control the number of snails and thereby protect the marsh grass from overgrazing. This is an excellent example of how confronting a long-held assumption with data can refine our understanding of the natural world.

An audio descriptive version of the film is available via our media player.