Quantifying the Potential for Marine Reserves to Enhance Ecological Resilience

Ecological resilience, the magnitude of perturbation a community can withstand and remain in a given state, is a critical component of ecosystem-based fishery management.  No-take marine reserves may enhance resilience by preserving a fraction of the community that can provide larvae to repopulate depleted areas in the event of an environmental or anthropogenic catastrophe.  However, intensification of mortality in unprotected areas caused by displaced fishing effort may decrease resilience relative to spreading the total fishing effort across an entire region.  We test whether reserves can increase resilience compared to conventional fishery management using a dynamic model of a groundfish community with structured predation and competition that cause a cultivation effect, generating alternative stable states.  Relative to conventional fishery management, reserves increase the range of initial predator densities that result in reaching the desired (predator-dominated) state, thus enhancing resilience.  This result holds even when fishing effort is displaced from reserve to unprotected areas in proportion to the areal coverage of reserves.  Furthermore, our results indicate that for degraded systems (those in the undesirable, competitor-dominated state), some combination of reserves and culling of competitors or stock enhancement of adult predators may be the most effective approach for restoration of the preferred state.