Seagrass (Zostera marina) restoration conducted through seeding of 0.5-1 acre plots has established >25 km2 of seagrass meadows in Virginia’s coastal bays. Long-term monitoring of the restoration provides insight into the dynamics of meadow expansion and the response of the meadow to disturbance from marine heatwaves. Expansion of the meadow is limited by depth (light limitation) in deeper areas and by warmer temperature in shallower areas. These limits interact with spatial position in the landscape to drive patterns of seagrass resilience. High temperature events in 2012 and 2015 have led to spatially variable declines and recovery patterns across two restored meadows. We combined long-term monitoring data (>12 years) with short-term observations before and after the high temperature events to understand the patterns of recovery and adaptability following temperature-induced declines.
Results/Conclusions
Spatial location within the landscape modified the exposure of different meadow areas to high-temperature stress. Recovery following the 2012 high temperature event varied based on the depth; deeper areas of the meadow showed low recovery and in some cases permanent loss compared to rapid recovery and continued natural expansion in moderate and shallow depths. In 2015, areas of the meadow that declined in response to high-temperature had experienced temperatures beyond the published temperature threshold value for longer periods of time compared to areas that received relief from high temperatures via tidal flushing with cool ocean waters. Following the 2015 high temperature event, these areas also recovered more slowly, remaining patchy for at least two years after the decline. The areas that experienced the most extreme loss also showed significant reduction in sediment carbon and nitrogen that had accumulated during the 16-year restoration, whereas other areas of the meadow continued to accumulate carbon and nitrogen. In both cases, the natural expansion of the meadow beyond the original restoration plots increased the resilience of the system by including areas that were more resistant to high-temperature stress and that recovered more rapidly than the original restoration plots.