MANGROVE MORTALITY AFTER HURRICANE MARIA

Abstract:

The ability of mangroves to absorb wave energy and trap sediment make them a vital resource for buffering coastal communities from extreme flooding. While mangroves aid in the protection of coastal communities during hurricanes, they are not immune to the damaging effects of these events. Here we provide observations of mangrove impacts on the island of Vieques, Puerto Rico following Hurricane Maria in 2017. Initial mangrove damage on the island shortly following the Maria event was relatively minor, however, in the months following significant die-off was observed over entire mangrove forest systems. Here, we explore the causes and resultant impacts of this delayed mass mortality. Month long deployments of turbidity sensors and water level loggers following mangrove damage indicate significant tidal attenuation in the tie-channels connecting lagoonal systems to the ocean, as well as predominantly ebb-dominated sediment transport. We infer this tidal attenuation to reflect frictional effects significant enough to reduce hydraulic conductivity during extreme precipitation, and ebb-dominated transport to potentially reflect enhanced erosion following vegetative die-off. Resultant and significant freshening of our lagoon during and directly following the Hurricane Maria event provided the predominant stressor responsible for delayed mangrove mortality. Recovery from such mass die-off events will likely take decades to achieve during which time the coastline is particularly prone to enhanced flooding and erosion due to resultant devegetation. Our results on both initial and delayed mangrove mortality provide important guidance on restoration efforts of mangrove forests and the limited protection such systems can provide in the years following initial hurricane-induced disruption.