Salt marsh ecosystems provide a critical transition zone important for humans and wildlife. Yet these critical ecosystems are being degraded and fragmented by urban development, pollution, and sea level rise. The persistence of salt marshes in the Gulf of Mexico is dependent on the dominant foundation species, black needlerush (Juncus roemarianus). J. roemarianus is a clonal macrophyte that accretes sediment to provide habitat for other marsh species. High genetic diversity in clonal macrophytes has been linked to greater resistance to disturbance and increased restoration success. To conserve ecosystem function and population persistence in the salt marsh, management of J. roemarianus must address the preservation of genetic diversity in natural and restored sites. We are conducting a population genetic analysis on J. roemarianus within irregularly flooded marshes on the Gulf coast between eastern Mississippi and the Florida panhandle. Using 19 microsatellite markers we calculated metrics to assess the current level of genetic diversity. A site in Mississippi was intensively sampled at a fine scale to examine the degree of clonal reproduction within the species. Samples were assigned to populations using Bayesian cluster statistics (STRUCTURE) to determine the scale of population structure on the Gulf coast.
Results/Conclusions
Populations had greater genetic diversity than expected from a highly clonal species with an average observed heterozygosity of 0.51. The results from the intensively sampled site in Mississippi indicate that the Juncus populations may not be as clonal as previously reported. Less than half of the 304 samples were clonal replicates and no clones were shared between sampling points separated by distances of one kilometer or greater. The two most distal sites located in Mississippi and Florida were highly differentiated (FST = 0.226) indicating population structure occurs on the Gulf coast. Our results have direct implications for current J. roemarianus restoration and management practices. The continued use of clonally propagated stock in restoration projects will create restored sites that do not reflect the genetic diversity in natural marsh systems. Population structure may also suggest local adaptation in black needlerush and therefore the need to select locally adapted genotypes for successful restoration.