Genetic Diversity and Spatial Structure of Spartina alterniflora at Four Spatial Scales

Spartina alterniflora, salt marsh cordgrass, is the dominant plant in coastal wetlands along the North American Atlantic coast. Ecological disturbances in salt marshes, such as coverage by wrack, disease, and eat-outs, affects Spartina marshes from the Gulf of Mexico to New England and may reduce the diversity of S. alterniflora clones within a population or alter other genetic characteristics of a population by eliminating some genotypes. Nine polymorphic microsatellite loci were used to quantify the genetic characteristics (e.g., allelic richness, diversity, polyploidy, fixation index) of the S. alterniflora populations at five salt marshes, as well as, to measure the spatial structure (size and shape of clones) of a single population in Upper Phillips Creek marsh (UPC), a marsh that experienced dieback. Over 250 individual plant samples were collected at three spatial scales for these experiments. Clones were found at all three spatial scales. However, at UPC marsh, over 53 unique genotypes were found corresponding to a high clonal diversity index of 0.944. All other marshes had indices above 0.9, except for Indiantown marsh, which had a low diversity index of 0.378. Although spatially separated by as much as 1, 15, 20, and 35 km, the five marshes were genetically connected as indicated by percent similarity calculations based on genetic similarity and geographic location. The high clonal diversity found and the large number of multilocus genotypes indicated that sexual reproduction and seedling recruitment are underappreciated processes that may contribute to marsh resilience and resistance to disturbance and climate change at the VCR LTER.