The contribution of seed banks to community dynamics in systems experiencing climate change is poorly understood. In the northern Gulf of Mexico, intensified tropical storms may alter the stage upon which communities develop and recover. Initial recovery following recession of storm surge events are driven by surviving individuals and response of potential flora already residing in soil seed banks. Therefore, predictions of community response to increased storm surge will require an improved understanding of seed bank composition and ability to withstand and recover from increased storm surge stress. The objectives of this study are: 1) to evaluate the composition and distribution of seed banks in major vegetation zones along a typical Gulf Coast transition and 2) to assess the effects of simulated storm surge on seed banks to predict community change with altered inundation regimes. We hypothesized that tides and storm surge result in well-mixed seed bank communities that are capable of acting as biological buffers following acute storm surge events. In June 2009, vegetation and seed bank sampling was conducted in six of the dominant vegetation zones in the intact coastal transition at Grand Bay National Estuarine Research Reserve in coastal Mississippi. We examined the germinable seed bank following a three-day exposure to full-strength seawater and provided additional freshwater flushing and heat shock treatments to capture the total pool of viable seeds.
Results/Conclusions
Preliminary analyses reveal a pattern of increasing plant species diversity with distance from the sea that is correlated with declining soil salinity. Our results also indicate very low germination in seed banks from more seaward communities, suggesting that salt and brackish marsh seed banks may be relatively unimportant in recovery of that vegetation type following disturbances. Seed bank communities exhibited similar zonation as the standing vegetation. Most seed banks were comprised of a subset of species present in the standing vegetation, as well as weedy species, indicating that disturbances would likely result mainly in replacement of species present in the former vegetation and possibly some invasives. A consideration of propagule banks may provide a clearer picture of ecosystem resilience to climate-driven changes. Communities lacking species in the seed bank that are more adapted to future conditions have reduced capacity to respond to rapid environmental changes associated with intensified storm surges that will increasingly be magnified by sea level rise. Assisted dispersal of propagules may be necessary to facilitate landward migration of species in these vulnerable coastal ecosystems.
