Corallivorous butterflyfishes as ambassadors of coral reefs

The concept of using one or a small group of species to indicate the condition of a larger community or ecosystem is not new. Hunting and gathering peoples, both past and present, intuitively apply the idea (Lee and Devore, 1968), and similarly early naturalists/conservationists like Aldo Leopold (1966) recognized the usefulness of the concept. A more recent example of the utility of the concept in the terrestrial environment is the finding that the decline of migratory songbird populations is an indication of degraded and hostile forests across the continental United States (Askins, 1995). To our knowledge, the concept of indicator species was first applied formally to marine organisms by the celebrated British marine biologist F.S. Russell in the 1930s (Fraser, 1962; Raymont, 1963). In a series of papers, Russell showed that certain species of zooplankton were indicative of water masses that contained commercially important species of fish. Russell emphasized that a good indicator species must be easily recognized and its distribution must characterize a particular mass of seawater. Two edited volumes address the use of marine organisms as indicators for detecting ecological impacts, usually from human activities, on marine ecosystems (Soule and Kleppel, 1988; Schmitt and Osenberg, 1996), with chapters on coral reefs (Hourigan et al., 1988; Jones and Kaly, 1996).