Abstract Summary
Long-term coral reef degradation leads to a significant coral loss and to a net decline in reef accretion, resulting in a permanent state of mediocrity. Such altered reefs have evolved into de facto novel ecosystems characterized by declining biodiversity, impaired ecological functions and services, and reef flattening, reducing its wave buffering and essential fish habitat roles. Cross-reef wave power reduction was preliminarily modeled to quantify restored reef performance and to analyze the effectiveness of idealized reef configurations in dissipating wave energy and reducing the wave power reaching the nearshore region. Preliminary analyses suggest that under highly flattened conditions wave energy and height attenuation can barely reach 14% and 3%, respectively, across reefs with a sparse fringe of Acropora palmata. But, coastal reefs with higher physical structuration can reduce more than 80% of wave power. Optimal reef centroid positioning has important implications for the design of coral reef restoration projects. If the goal is to optimize the degree of coastal protection provided by a restored reef, without seabed modification (e.g. excluding a submerged structure that decreases effective water depth), then the ideal restoration location may not be at the existing reef crest, but closer to shore, highlighting the importance of shallow coastal reefs rehabilitation. The integration of long-term projections generated by stochastic demographic models for A. palmata, A. cervicornis, and Orbicella annularis parameterized with long-term data under present environmental conditions in Puerto Rico suggests that these species might face a high extinction risk under projected climate change-related stress. Recurrent coral mortality events associated to multiple stressors result in negative population growth rates (λ) and in a threat to the long-term success of reef rehabilitation. Regardless of small spatial scale success, reef rehabilitation strategies can have very limited impacts on wave attenuation and enhancing coastal resilience unless a significant increase in the magnitude, spatial and temporal scale of interventions is achieved, and unless sources of mortality are curtailed. The integrated role of wave numerical models and demographic models is discussed as a tool to address the simulated impacts of multiple spatial designs of reef rehabilitation interventions.
