Testing for top-down control: can post-disturbance fisheries closures reverse algal dominance?


T.R. McClanahan, Wildlife Conservation Society, Marine Programs, 2300 Southern Boulevard, Bronx, NY 10460, USA. E-mail: tmcclanahan@wcs.org


  1. The response of fish, sea urchins, benthic cover, herbivory, and predation on sea urchins were studied over a 14-year period in and out of a recently established fully closed and fished atoll reef lagoon of the remote Glover's Reef, Belize.
  2. Closure from fishing was predicted to result in the recovery of predatory fish and herbivores, herbivory rates, and subsequently reduce erect algae and lead to the recovery of herbivore resistant and calcifying taxa such as hard corals and calcifying algae. Recovery of predatory fishes was the largest response to closure and the herbivore response was weak and no corals and calcifying algae changed in the predicted direction.
  3. Hard corals declined where they were most abundant and all sites appear to have reached a stable point of ~15% cover by the end of the study. Generalized and possibly opportunistic carnivores, such as jacks, barracuda, groupers, snappers, grunts, and sparids showed the greatest increases and there was a trend towards more small-bodied herbivores such sea urchins and damselfish in the open and a slight gain in large herbivores in the closed area, but this had little effect in increasing total herbivory.
  4. Factors that may have influenced this unexpected response include: (1) a complex food web that did not produce a simple cascade response; (2) attenuation of the cascade effect towards the lower trophic levels; (3) insufficient compliance, closure time, and space; (4) a post- rather than pre-disturbance establishment of the closure; 5) habitat or site specificity; and (6) overriding environmental disturbances, such as oceanographic oscillations and a warming climate.
  5. The results suggest a need to further evaluate fisheries management systems, contingencies, and interventions that will promote coral reef resilience to climate change and ecosystem sustainability.

    Copyright © 2011 John Wiley & Sons, Ltd.