No abstract

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.

No abstract

Diseases of marine organisms, and corals in particular, have been reported with increasing frequency over the past 3 decades. Although little is known about resistance to disease in corals, a potential mechanism of defense is the production of antimicrobial compounds that protect corals from microbial pathogens. We assessed the antibacterial activity of crude aqueous extracts from 3 common Hawaiian reef corals, Montipora capitata, Porites lobata, and Pocillopora meandrina, against 9 strains of bacteria. The bacteria selected included known coral pathogens, potential marine pathogens found in human waste, and bacteria previously identified from the surfaces of Hawaiian corals. Extracts from all 3 coral species exhibited high levels of antibacterial activity. Overall, 54.3% of assays resulted in bacterial growth inhibition. In addition, 9.9% of extracts stimulated the growth of certain bacteria. Although levels of overall antibacterial activity did not differ significantly among coral species (ranging from 40.7% of assays for P. meandrina to 63.0% of assays for M. capitata), the 3 species exhibited a high degree of selectivity as demonstrated by significant variability in their effects toward specific bacteria. Extracts also exhibited intraspecific variability, both within and between sites, and significant site-by-species interactions were observed against 6 of 9 bacterial strains. In M. capitata, healthy corals had significantly higher levels of antibacterial activity than those affected by Montipora White Syndrome, and affected tissues had significantly higher levels of antibacterial activity than unaffected tissues. Variability in antibacterial activity of Hawaiian corals may, in part, explain differential susceptibility to disease at the colony, species, or population level.

No abstract