Elevation influences salt marsh crab abundance, diversity, and burrowing

Abstract

Identifying drivers of the spatial distribution of organisms is a key aim of ecology. Salt marsh ecosystems can exhibit extreme gradients in abiotic conditions, including orders of magnitude differences in physical conditions across the marsh platform, which may contribute to the spatial distributions of organisms found in marshes. Small-bodied consumers, such as crabs, have been identified as key residents of salt marshes, with strong impacts on salt marsh persistence and stability at local scales. However, due to a lack of consensus regarding crab impacts across larger biogeographic scales, continued investigation into the factors driving crab community spatiotemporal dynamics is needed. We used an observational approach to investigate the small-scale spatial patterns and environmental correlates of marsh crab abundance, burrowing activity, and community composition in a representative southeastern US salt marsh. We documented contrasting trends in crab abundance and burrowing activity across the marsh platform elevation gradient, with abundance increasing and burrow density decreasing from the creek bank to forest edge. Crab diversity generally increased with distance from tidal creeks, though the effect of marsh zone on crab diversity was site-specific. Finally, we demonstrated elevation as the key environmental predictor of marsh crab abundance, burrowing activity, and community diversity and identified specific elevations that serve as breakpoints in those metrics. Our results contribute to reconciling differences between small-scale manipulative experiments and large-scale biogeographic sampling of these ecosystem engineering salt marsh residents.