A Synthesis of Plant Mass Mortality Events in Coastal Ecosystems

Abstract Around the world, mass mortality events are disrupting the ecological and economic stability of shorelines. To better understand mechanisms of mass mortality in coastal ecosystems, we provide a global synthesis of over 250 reports of plant mass mortality events in six coastal ecosystems: coastal freshwater forests, tidal freshwater marshes, salt marshes, mangrove forests, seagrass meadows, and kelp forests, highlighting commonalities. Mass mortality events were associated with both climate and land-use change drivers in all six coastal ecosystems. Furthermore, increases in disturbance intensity and frequency, including climate extremes, and compound disturbances were key aspects of mass mortality events. Land-use change disturbances that altered hydrology, nutrient availability, and trophic structure often interacted with climate stressors, leading to mass mortality events. Therefore, beyond global climate mitigation, remediating local land-use disturbances represents a tractable opportunity for intervention. Insights from this synthesis may help managers to anticipate mass mortality events and prevent future habitat loss.