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From Long-Term Data to Understanding: Toward a Predictive Ecology
2015 LTER ASM Estes Park, CO - August 30 - September 2, 2015

Effects of a gradient in herbivore pressure on coral reef algal community dynamics

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Samantha Davis
Russell Schmitt
Sally Holbrook
Andrew Brooks
Tom Adam

Top-down control by herbivores has been implicated as a key process influencing transitions among coral community states, especially in cases of algal dominance on Caribbean reefs. Though the importance of herbivores to coral reef benthic communities is no longer in question, we currently know very little about how the strengths of consumer effects varies at different points in succession. If the herbivores in a system exert their greatest influence on early successional stages, but are unable to control later-successional stages, the positive indirect effects of herbivores on coral recruitment and growth may be limited. This could also lead to a potential hysteresis or lag in the algal response to herbivory – where higher herbivore pressures are required to limit late successional stages than early stages. To determine how the effects of consumer pressure vary at different stages of algal succession, we manipulated 1) herbivore pressure and 2) initial algal community in field experiments in the lagoon and fore reef habitats of Moorea, French Polynesia. After two years, we found evidence that herbivores may have differential abilities to exert top-down control of algal communities depending on the developmental stage of the algal community, though these results were spatially variable within the reef habitats of Moorea.

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