Ecosystem management frequently aims to manage resilience yet measuring resilience has proven difficult. Here, we quantify the ecological resilience of the largest reef in the Caribbean and map potential benefits of marine reserves under two scenarios of greenhouse gas emissions. Resilience is calculated using spatial ecological models and defined as the probability of a reef remaining in its coral-dominated basin of attraction such that it does not flip into an alternate, algal-dominated attractor. In practice, resilience is the probability that coral populations will maintain the ability to exhibit a recovery trend after acute disturbances such as hurricanes. The inputs required to estimate resilience are a reef's initial state, physical environment, and disturbance regime. One major driver of reef resilience is herbivory by parrotfish and recent action to protect parrotfish in Belize was found to have increased resilience 6-fold. However, the expected benefits of parrotfish protection to future coral cover were relatively modest with only a 2- to 2.6-fold improvement over a business-as-usual scenario, demonstrating how resilience and ecosystem states are decoupled. Global action to reduce greenhouse gas emissions had little impact on average coral state unless it was accompanied by local controls of fishing. However, combined global and local action reduced the rate of reef degradation threefold. Operationalizing resilience explicitly integrates available biophysical data and accommodates the complex interactions among ecological processes and multiple types of disturbance.