Predation-induced morphological and behavioral defenses in a hard coral: implications for foraging behavior of coral-feeding butterflyfishes

In clonal organisms, such as corals, one consequence of partial predation may be an elaboration of defenses in remaining portions of the clone, thereby reducing the probability or severity of future predation events. Inducible defenses have been found in terrestrial and marine plants and in several taxa of marine invertebrates. Predators can detect differences in various aspects of prey quality that translate into preferences for certain prey items. Differences in quantity or types of defenses may determine which species, individuals or parts of a prey item are consumed. Coral-feeding butterflyfishes show distinct preferences for certain coral species, and may prefer particular individuals of a species over others. This study examines the potential for inducible defenses in a hard coral in response to grazing by a natural coral predator, the butterflyfish Chaetodon multicinctus. Pairs of genetically identical fragments of the Hawaiian coral Porites compressa were exposed to grazed and ungrazed treatments. These colonies were then offered to naive fish in preference tests at various intervals following the treatment period. Grazing by butterflyfishes induced changes in polyp behavior (prolonged withdrawal of coral polyps) in the short term, and increases in nematocyst density over the longer term, and these changes were associated with reductions in palatability and subsequent predation rates on the damaged corals. These inducible responses may play a role in regulating the intensity of grazing, and ultimately territory size and the density of corallivorous reef fishes.