Using threat maps for cost-effective prioritization of actions to conserve coastal habitats

Marine coastal habitats provide valuable ecosystem services, including food provision, carbon sequestration, and coastal protection, but they are highly threatened by human activities. The multitude of human stressors affecting coastal habitats renders their conservation a difficult task for environmental agencies with limited budgets. This study, using seagrass meadows – one of the world's most threatened coastal habitats – proposes a transparent framework for the conservation of coastal habitats that links information from habitat and threat maps to conservation actions, and their costs. The proposed framework and the use of a predictive model of seagrass loss allowed the selection of the most cost-effective actions to abate stoppable threats (trawling and anchoring), while avoiding areas affected by threats that are more difficult to manage, such as coastal development. The relative improvement in cost achieved by using the proposed approach was examined by comparing with other common prioritization criteria that do not consider cost, including choosing sites based on threat level or habitat cover alone. The establishment of anti-trawling reefs was found to be the most cost-effective action to achieve the European Union conservation target for the protection of seagrass Posidonia oceanica meadows. The number of anti-trawling reefs and their establishment location was sensitive to fine-scale information on the distribution of fishing activities. The proposed approach always conserved the same habitat for lower cost than prioritization schemes that focus actions in areas of highest seagrass coverage or highest threat level. The study results suggest that conservation actions should not be prioritized on the basis of habitat maps and/or threat maps alone. Impact assessment and habitat vulnerability at a local scale would greatly benefit from detailed knowledge of the spatial distribution of stressors. At the same time, methods of scaling up the quantitative impact of stressors are urgently needed to understand their relationship with seascape-wide habitat coverage and to inform conservation of coastal habitats.