Strategies for Successful Mangrove Living Shoreline Stabilizations in Shallow Water Subtropical Estuaries

Mangrove living shorelines are an effective alternative to hard-armoring, which combat erosion while also increasing habitat. To improve the success of future mangrove deployments, an experimental Rhizophora mangle living shoreline was deployed within Mosquito Lagoon, FL. A factorial design was used to test the impact of mangrove age, breakwater presence, and mangrove placement on mangrove survival and growth. Environmental factors were monitored to isolate the reason for mangrove mortalities. Mangrove age was represented by 3 developmental stages: seedlings at 11-months-old, transitionals at 23-months-old, and adults between 35 and 47-months-old. Mixed mangrove age groups were included to identify if seedling survival could be facilitated by the presence of transitionals and adults; control groups were used to test the impact of restoration materials on recruitment of wrack and mangrove propagules. The majority of mangrove mortalities (62%) occurred 2 months after the onset of high-water season and these dead mangroves showed signs of flooding stress. Breakwaters alleviated stress through the reduction of water velocity and wave height, and increased the odds of survival by 197% and 437% when mangroves were planted in the landward and seaward rows, respectively. Due to their larger stems and greater number of prop roots, older mangroves were better able to survive; compared to seedlings, transitionals increased survival odds by 186% and adults by 1087%. For treatments composed of adults and a breakwater, 88% of the mangroves survived and 64% of these survivors produced flowers or flower buds by 12 months after the restoration. Planting seedlings haphazardly among older mangroves did not attenuate enough wave energy to significantly increase seedling survival, and the complexity of restoration materials did not significantly impact propagule or wrack abundance