Expansion of Tidal Marsh in Response to Sea-Level Rise: Gulf Coast of Florida, USA

Understanding the influence of future sea-level rise (SLR) on coastal ecosystems is improved by examining response of coastlines during historic periods of SLR. We evaluated stability and movement of the estuarine intertidal zone along eastern Gulf of Mexico, known as the “Big Bend” of Florida. This relatively undeveloped, low-energy coast is dominated by broad expanses of tidal marsh, providing an opportunity to observe unobstructed response of a coastal ecosystem to SLR. Features from nineteenth century topographic surveys and late twentieth century satellite imagery were compared. Relative change was calculated for intertidal area and lateral migration over 120 years, a period when tidal amplitude increased in addition to SLR. Loss of tidal marsh at the shoreline was −43 km2, representing a 9 % loss to open water. At the same time, 82 km2 of forest converted to marsh and 66 km2 of forest converted to forest-to-marsh transitional habitat. The result was a net regional gain of 105 km2 of intertidal area, an increase of 23 %, constituting a marine transgression of coastal lowlands. Forest retreat was lower at zones of high freshwater input, attributable to salinity moderation and was further complicated by coastal morphology and land-use practices. Shoreline migration may not represent full extent of habitat change resulting from SLR in regions with low coastal gradients. Forest retreat was consistent with what would be predicted by an inundation model; however, shoreline loss was considerably less, resulting in a net increase in intertidal area in this sediment-limited coast.