Russell Milne

Sedimentation is a major coral reef stressor, with effects including suppressing algae consumption by herbivorous fish. This puts pressure on reef fish populations and the fisheries that harvest them. Deforestation causes much sedimentation on reefs, and is an ongoing concern in many tropical island states. Although ecosystem processes like deforestation and fish population dynamics are usually far from equilibrium, explicitly time-dependent analyses of reef fish vulnerability to deforestation are rare. Additionally, optimization methods for fisheries on heavily sedimented reefs are generally unexplored. Here, we construct a model coupling four reef fish functional groups with seabed dynamics and deforestation, parametrized to represent a wide variety of tropical coastal forests. We show that with predicted human population increases, highland deforestation could cause omnivorous fish abundances to halve within 15-30 years, and piscivorous fish and top predators to do so around 20 years later. In contrast, piscivorous fish and top predators are resilient to lowland deforestation, and herbivorous fish populations often recover after initial declines during sedimentation pressure. We demonstrate that flexible fishing approaches could lead to high and temporally stable populations of most functional groups, offsetting sedimentation-related stress. We show that the combination of deforestation and increased fishing demand due to human population growth may cause medium-term local reef fish extirpation. Our results provide sustainability guidelines for reef fisheries, and demonstrate nonlinear interactions between overfishing and deforestation.