PARENT SESSION
Oral Session # 54: Coastal Ecosystems: Salt Marshes.
Presiding: P Ringold
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 105.
Spatial segregation of New England marsh plants across an estuarine salinity gradient.
Mullan, Caitlin*,1, Silliman, Brian1, Bertness, Mark1, 1 Brown University, Providence, RI, USA
ABSTRACT- While it has long been recognized that marsh plant community composition shifts across estuarine salinity gradients, the mechanisms responsible for these species shifts have never been experimentally examined. We conducted a series of experiments in southern New England marshes to investigate the roles of physical and biotic interactions in driving species segregation along this gradient. Greenhouse studies revealed that all of the common plants in this system grow better in fresh water than in full strength salt water. Field transplant experiments, using 10 common plants in the system, showed that when salt marsh plants were transplanted to tidal freshwater marshes, in the absence of neighbors (without competition) they grew better than they did in salt marshes, but were strongly suppressed when neighbors were present. In contrast, when freshwater marsh plants were transplanted to salt marshes, they did poorly and generally died with or without neighbors (competition) present. These results suggest that while fresh marsh plants are limited from salt marshes by physiological stress, salt marsh species are limited from fresh marshes by competitive displacement. Thus, theory developed along vertical intertidal gradients, that superior competitors dominate physically benign habitats and displace weaker competitors to physically harsh habitats, can be further generalized to horizontal landscape-scale gradients. Experimental results contribute to our understanding of the organization and assembly of the full range of estuarine marshes and have important implications for predicting how marsh plant communities will respond to altered hydrology (e.g. freshwater diversions, sea level rise), coastal eutrophication, and invasive species.
Key words: wetland plant communities, species distributions, environmental gradients, salt marsh