Hydrodynamic habitat thresholds for mangrove vegetation on the shorelines of a microtidal estuarine lagoon
David Cannon, Kelly M. Kibler, Melinda Donnelly, Giovanna McClenachan, Linda J. Walters, Annie Roddenberry, Jessica Phagan
Abstract
Although understanding the requisite hydrodynamic habitat for mangrove vegetation is vital for successful restoration efforts, few studies have quantitatively assessed the in-situ tolerance of mangroves to relevant physical forcing mechanisms. In this work, hydrodynamic thresholds for the persistence of mangrove vegetation (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa) are assessed using a hindcast wind-wave model coupled with a high-resolution shoreline survey, with analysis including 383 km of shoreline located in a microtidal estuary along the Atlantic coast of Florida (north Indian River Lagoon, USA). Observed mangrove distribution patterns were most strongly correlated with the modelled wave climate (p < 0.001) and measured intertidal slope (So; p < 0.001), and mangrove presence probabilities were maximized for sample sites characterized by low slopes (So < 0.5) and weakly energetic waves (80th percentile wave height: H80 < 2.5 cm). Critical wave thresholds (mean ± 95% confidence interval) of H50=4.2 ± 0.4cm and H80 = 8.0 ± 0.5cm were estimated for 50th and 80th percentile wave heights, respectively, representing the wave climate limits above which mangrove presence probabilities fall below 50%. Low intertidal slopes were observed to enhance mangrove wave tolerance (So≅0; H80 = 9 cm) while high slopes led to dramatic reductions in threshold wave heights (So≅1; H80 = 4 cm). These results have important implications for future restoration efforts, providing the first available quantitative wave thresholds for mangrove habitat suitability.