Impact of conservation areas on trophic interactions between apex predators and herbivores on coral reefs
Rizzari, JR and Bergseth, BJ and Frisch, AJ, Impact of conservation areas on trophic interactions between apex predators and herbivores on coral reefs, Conservation Biology, 29, (2) pp. 418-429. ISSN 0888-8892 (2015) [Refereed Article]
Apex predators are declining at alarming rates due to exploitation by humans, but we have yet to
fully discern the impacts of apex predator loss on ecosystem function. In a management context, it is critically
important to clarify the role apex predators play in structuring populations of lower trophic levels. Thus,
we examined the top-down influence of reef sharks (an apex predator on coral reefs) and mesopredators
on large-bodied herbivores. We measured the abundance, size structure, and biomass of apex predators,
mesopredators, and herbivores across fished, no-take, and no-entry management zones in the Great Barrier
Reef Marine Park, Australia. Shark abundance and mesopredator size and biomass were higher in no-entry
zones than in fished and no-take zones, which indicates the viability of strictly enforced human exclusion areas
as tools for the conservation of predator communities. Changes in predator populations due to protection in
no-entry zones did not have a discernible influence on the density, size, or biomass of different functional
groups of herbivorous fishes. The lack of a relationship between predators and herbivores suggests that topdown
forces may not play a strong role in regulating large-bodied herbivorous coral reef fish populations.
Given this inconsistency with traditional ecological theories of trophic cascades, trophic structures on coral
reefs may need to be reassessed to enable the establishment of appropriate and effective management regimes.