Low-lying coastal ecosystems are among the first to be directly impacted by hurricane disturbance and sea level rise. Coastal species may cope with environmental changes over the short term but eventually they will be eliminated unless migration occurs. Migration depends on the ability to colonize environmentally suitable areas. We hypothesize that hurricane-generated storm surge disassembles landward communities dominated by species intolerant of high salinity pulses, thereby enabling species from seaward positions to establish further inland. In Summer 2009, five transects were established at points along East Bay River, a tidal river ecosystem in northwest Florida. Each transect was surveyed for elevation and extended perpendicular to the river into upland habitat to include 1m, 2m, and 3m changes in relative elevation from river’s edge. Nine 2m x 1m plots were established haphazardly in each of the three elevation classes alongside each transect (total n = 135). Plant species were identified and their cover estimated prior to application of experimental storm surge treatments in late August; three of the plots in each elevation class along each transect were not manipulated. Percent mortality and soil salinity were measured in each plot a month later to determine short-term effects of the treatment.
Results/Conclusions
Ordination of the pre-surge vegetation plots indicated that the brackish marsh had little in common with the other vegetation and was low in diversity. With brackish plots omitted, vector fitting showed that composition was significantly correlated with topographic position relative to the river and distance from the sea. With distance from the sea, species intolerant of salinity dropped out of the community. Mortality attributed to the surge treatment was lowest in the brackish marsh and waterlogged plots closest to the river. Species at the highest elevations also had low mortality, whereas species in plots of intermediate elevation where the surge infiltrated slowly had the highest mortality. Because the plots adjacent to the river were often slightly flooded, it is likely that the surge treatment was quickly diluted. Also, we observed that the storm surge infiltrated quickly in the highest elevation plots that are underlain by deep sands. These results suggest that the effects of the storm surge may be muted or accentuated, depending on the existing environmental conditions. We will continue to monitor recovery and natural regeneration of vegetation in these plots to determine whether storm surge can drive more permanent shifts in community composition consistent with landward migration.
