The Stability and Regeneration of Seagrass Meadows During Hurricanes

Msc. thesis

Tropical seagrass meadows are vital coastal ecosystems threatened by both storm activity and human interference. Intense hurricane activity in the subtropical Atlantic has been projected to increase by the late 21st  century, having uncertain consequences for seagrass ecosystems in the region. This study investigated the responses of seagrass meadows to hurricane-related nearshore processes in the current and future storm climates. Further, the impacts of human interference and the sensitivity of meadow formation were studied. This was achieved by coupling the morphodynamic model XBeach and the agent-based seagrass community model SMEAGOL. The development of Thalassia testudinum  meadows was simulated with cycles of 40 hours of morphodynamics followed by one year of growth, over a one-dimensional cross-shore transect across Galion Bay, St Martin. Both seagrass leaves and the biogeomorphic landscapes they form are signicant in attenuating wave energy. Relative wave attenuation by Thalassia  meadows is reduced under the storm surge and waves generated by a category 5 hurricane. Removal of the seagrass canopy by changes in the water quality results in a signicant reduction in wave attenuation and coastal protection potential. Untouched Thalassia  meadows in shallow, reef-protected habitats are unlikely to experience widespread loss as a result of increasing storm activity in the future. The tipping point, if it exists, is certainly above four direct category 5 hurricane strikes in a year. A meadow fragmented in exposed areas by propeller scarring or other human interferences is unlikely to recover, and renders the meadow vulnerable to further damage in the event of a storm. Regeneration of Thalassia  meadows by sexual reproduction is a slow and sensitive process irrespective of the storm climate, remaining susceptible to complete reversal by storm impact for decades. As such, meadows removed by a combination of hurricanes and human activity may never recover.