Predator Outbreaks

Crown of thorns starfish. Photo @ David Burdick
Top: Crown-of-thorns starfish (Acanthaster planci) on coral. Photo © Wolcott Henry 2005/Marine Photobank; Bottom: Longspine sea urchin (Diadema setosum), Kenya. Photo © Tim McClanahan

Top: Crown-of-thorns starfish on coral. Photo © Wolcott Henry 2005/Marine Photobank; Bottom: Longspine sea urchin (Diadema setosum), Kenya. Photo © Tim McClanahan

Coral predators, or corallivores, can cause significant damage on coral reefs when population outbreaks occur. Such predators include a range of echinoderms and mollusks. Coral predators cause tissue loss in corals because feeding involves the removal of live coral tissue. The amount of tissue loss depends upon the number and type of coral predator, their size, and the frequency of their feeding.

Coral predators that can impact coral reefs include:

Overabundance of COTS and Drupella can accelerate bioerosion, reduce coral cover, reduce topographic complexity, and drive phase shifts from coral to algal-dominance on a reef. Although sea urchins are also coral predators (because they graze on corals and play a major role in bioerosion), they are also critically important herbivores on coral reefs.

Corallivorous Fishes

In addition to COTS, sea urchins, and Drupella, some fishes (such as butterflyfishes, parrotfish, puffers, triggerfish, filefish, wrasses, and damselfish) also consume live coral tissue. Although corallivorous fishes are not included in this section, a brief discussion of their role in coral reef ecosystem dynamics is included here.

Scientists debate the role of corallivorous fishes in coral reef ecosystems, and some controversy exists over whether these fishes have a net positive or negative effect on coral reefs. For example, Rotjan and Lewis ref suggest that while corallivore damage can range from minor to lethal, a growing body of evidence suggests that even limited removal of coral tissue and skeleton has potentially adverse consequences for coral growth and/or fitness. McClanahan et al. ref suggest that predation influences recovery of transplanted corals in Kenya; these authors found that the lowest survival of transplants occurred in the unfished marine parks potentially due to predation. Some studies have found that damage from fish predation is worse than damage from tourism. ref

By contrast, other studies ref have found that while increased numbers of parrotfish may increase the predation rate upon juvenile corals, the overall effect of such herbivores on corals appears to be positive. This is because herbivorous fishes (e.g., parrotfishes) play an important role in facilitating coral recruitment, growth, and reproductive capacity. ref Therefore, current evidence suggests that the benefits of herbivory ref outweigh the potentially adverse impacts of corallivory. ref Future research is needed to assess the role of corallivory as a vector of coral disease or in combination with other stressors (e.g., algal competition, changes in ocean chemistry). ref

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