The ecology and evolution of seaweed-herbivore interactions on coral reefs

Because seaweeds grow rapidly and are easy to manipulate, they have provided a wealth of information on how consumers affect coral reef community organization. Herbivory is the dominant force affecting the distribution and abundance of reef seaweeds, with seaweed morphology, structure, chemistry, and competitive ability often being a function of herbivory by fishes and larger invertebrates. Seaweeds that deter these herbivores become the favored living sites and foods of smaller, less mobile mesograzers that derive protection from consumers by associating with defended hosts. Host specialization reduces mesograzer susceptibility to predation through crypsis, sequestration of chemical defenses, and reduction of encounters with consumers. Mesograzers can serve as either pests or mutualists, depending on their feeding behavior and how it affects the host. Some mesograzers protect hosts from competitors while others attack hosts, causing induction of chemical defenses. More limited studies of corals and sponges parallel findings for seaweeds.