Territorial damselfishes facilitate survival of corals by providing an associational defense against predators

摘要

Territorial defense by the herbivorous damselfishes, Stegastes nigricans and S. lividus, benefits the hermatypic corals growing inside their territories. Coral diversity was significantly higher inside damselfish territories at 2 sites in Moorea, French Polynesia, and at 1 site in Guam, Mariana Islands. In Guam, this pattern was stable for at least 10 yr. Certain coral species, including Pocillopora damicornis, were found only inside damselfish territories at these sites. All fishes, including coral-feeding butterflyfishes, approaching territories of Stegastes spp. were vigorously chased. Colonies of P. damicornis inside territories were not preyed upon by any potential intruders. When transplanted outside of territories, colonies of P. damicornis were preyed upon rapidly by several species of butterflyfishes. Feeding rates of individual butterflyfishes on transplanted P. damicornis colonies were initially very high and decreased significantly over 30 min as accessible coral tissue was removed. In contrast, transplanted Porites rus, a major component of the reef outside of territories in Guam, attracted no predators. This study suggests that territorial damselfishes provide an associational defense for certain coral species that live inside their territories, whereas these species settling outside territories experience heavy predation, resulting in suppressed growth and negligible survival. This demonstrates the potential importance of this type of positive indirect interaction between species in structuring coral reef communities, that protection from predation by coral-feeding fishes is a mechanism by which damselfishes can enhance coral diversity on reefs, and that this association can remain stable for many years.