Low lying coastal ecosystems of the Mississippi River deltaic plain are vulnerable to sea-level rise and hurricane disturbances and exotic species invasions. In flooded backswamps, widespread replacement of native species by exotics also threatens the ecological integrity of the floating aquatic communities. Exotic-dominated communities may differ from native ones in their ability to cope with climate change and natural disturbances that are common in this ecosystem. Here, we test the resiliency of invaded vs. un-invaded freshwater floating aquatic communities to simulated sea-level rise and hurricane storm surge. We hypothesized that greater abiotic stress would decrease resilience in all communities, but that invaded assemblages would be less resilient than un-invaded ones. We established microcosm experiments and constructed fully invaded, partially invaded, and un-invaded floating aquatic communities. These communities were exposed to chronic and acute salinity stress at levels mimicking saltwater intrusion from sea-level rise and hurricane storm surge, respectively.
Results/Conclusions
Consistent with our hypotheses, community resiliency (expressed as change in plant cover) was negatively related to stress and degree of invasion. Total plant cover of invaded and un-invaded communities decreased significantly with increased stress. At the highest salinity included in our experiment (12 ppt), total plant cover of invaded communities was significantly lower than in un-invaded ones, suggesting that they are indeed less resilient. Exotic species that evolved under disturbance regimes that differ from those in their introduced range may be ecologically naïve and unable to successfully rebound following disturbances that are novel to them. Thus, climate change associated disturbances could benefit native species by reducing the competitiveness of invasives and thereby creating restoration opportunities in coastal aquatic plant communities.