[Coral-List] What is a keystone species?

Bruno, John jbruno at unc.edu
Wed Sep 10 18:06:43 EDT 2014

Re, the recent posts "Keystone coral species in the Panama region”: I thought it would be useful to explain that a keystone species is defined as one that has a large effect on its community relative to its total mass.  Thus a habitat forming coral cannot, by definition, be a keystone.  Keystones have a large per captia (or biomass scaled) effect.  Their influence is not simply a result of their numerical dominance.  Given the very large proportion of biomass made up by top predators like sharks on “pristine” reefs, they too are very unlikely to be keystones.  (I also doubt that sharks have an exceptional effect even ignoring their biomass dominance when present, but that is a different argument). Generally, only very uncommon predators meet these criteria, e.g., wolves and sea otters.

Habitat forming species like corals are instead termed “foundation species” and they have a large community effect (usually via habitat provision and the modification of environmental conditions) but their mass standardized effect is not exceptional.

Bruno, J. F., and M. D. Bertness. 2001. Habitat modification and facilitation in benthic marine communities. Pages 201–218 Marine Community Ecology. Sinauer, Sunderland, MA.

Power, M. E., D. Tilman, J. A. Estes, B. A. Menge, W. J. Bond, L. S. Mills, G. Daily, J. C. Castilla, J. Lubchenco, and R. T. Paine. 1996. Challenges in the quest for keystones. BioScience 46:609–620.

Also see:




John Bruno
Professor, Dept of Biology
UNC Chapel Hill

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