Effects of Marsh Edge and Surface Elevation on Salt Marsh Infauna and Food Value for Nekton Predators

The relative importance of edge and elevation on infaunal distribution patterns within a intertidal Spartina alterniflora salt marsh was examined by collecting infauna on the nonvegetated intertidal and within the marsh at distances of one, three, five, and ten meters from the marsh edge. Densities of most species of polychaetes and crustaceans within marsh vegetation were highest one meter from the marsh edge compared with densities farther from the marsh edge during most of the year. Distributions of surface-dwelling infauna had the strongest relationship with marsh edge, whereas some subsurface feeders were not affected by proximity to marsh edge. Through the use of Multivariate Analysis of Covariance, I found densities of overall infauna to be consistently related to marsh edge throughout the year even after accounting for elevation effects. Infaunal abundance was related to elevation only during the early spring, mid-summer, and late fall. These data suggest that edge effects are often more important than elevation effects in controlling ecological factors that affect infaunal distributions within the salt marsh. The relative value of marsh surface and associated intertidal infaunal populations to predators was examined by two laboratory experiments (in May and August, 1995). The growth of several common marsh predators was compared after foraging for two weeks on sediments from three different microhabitats along the intertidal salt marsh (nonvegetated intertidal and within the marsh at distances of one and ten meters from the marsh edge. In each experiment, growth rates for predators were below natural growth rates reported in the literature, and these rates were not significantly different among microhabitats. Because this information indicates that predator growth was probably food-limited in experimental chambers, growth rates in these experiments were probably not an accurate measure of microhabitat value.