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

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.

Inter-specific variation in susceptibility to grazing among common reef corals

“…However, the present study and other recent findings (e.g Pratchett 2007, Gochfeld 2010 have all demonstrated that polyp feeding corallivores are a highly selective functional group that consumes considerably more coral tissue than previously suspected. They are capable of having significant effects upon the structure of the coral community, especially after major disturbance events (Bellwood et al 2006, Gochfeld 2010. The energetic cost imposed by coral-feeders upon coral colonies still needs to be quantified and incorporated into coral reef resilience models, as it is likely that this chronic stress will interact with and be potentially compounded by future anthropogenic stresses.…”

“…Further, the intensity of predation on these very small colonies was the lowest of all size classes, which suggests predation-induced mortality by polyp-feeders on juvenile corals is only likely to occur when these small colonies are the only remaining corals left on a reef (e.g. Samways 2005, Gochfeld 2010). Likewise, very large corals are also expected to experience a lower net effect from chronic predation as the impact of tissue loss is dispersed over a larger surface area, with larger colonies having a greater capacity for regeneration (Oren et al 2001).…”

“…These disturbances have led to major changes in the community structure of coral assemblages (e.g. Gochfeld 2010). Gochfeld's (2010) observations indicate that Acropora and Pocillopora colonies have become extremely rare on some reefs with the distribution of these colonies restricted to spatial refuges inside herbivorous and aggressive damselfish territories.…”

“…Gochfeld 2010). Gochfeld's (2010) observations indicate that Acropora and Pocillopora colonies have become extremely rare on some reefs with the distribution of these colonies restricted to spatial refuges inside herbivorous and aggressive damselfish territories. When colonies of Pocillopora damicornis were experimentally transplanted away from these territories, rapid and intense predation occurred and resulted in these colonies being overgrazed, with up to 85% of accessible tissue being removed within 88 h (Gochfeld 2010).…”

Contrasting Responses in the Niches of Two Coral Reef Herbivores Along a Gradient of Habitat Disturbance in the Spermonde Archipelago, Indonesia

“…While wider foraging ranges may conversely result from reliance on specific, rare resources, their robust jaw morphology (Bellwood, 1994) and a gut able to process high sediment loads (Choat et al, 2002) support the first interpretation, as they allow the fish to process more foods with differing isotopic values. In contrast, farming damselfish actively select the composition of their 1m 2 territories (Hata and Kato, 2004;Ceccarelli et al, 2005) which counterintuitively can also lead to higher diversity via intermediate disurbance (Gochfeld, 2010). Their restricted niche values suggest that they are reduced in the number of food sources that they assimilate in comparison to the parrotfish.…”