The impacts of bioturbation by common marsh crabs on sediment erodibility: A laboratory flume investigation.

Accelerating sea-level rise (SLR) threatens salt marshes globally, and thus understanding how these ecosystems respond to this stress is vital to increasing their resiliency. In order to maintain their surface elevation as sea level rises, salt marshes must add below ground biomass and accrete sediment. In many cases, biota can significantly affect marsh accretionary and erosional processes by stabilizing or helping to mobilize sediment, which in turn can profoundly affect the morphological evolution of the marsh. However, these effects are poorly understood. Bioturbation by dense populations of the marsh crab Sesarma reticulatum has been found to facilitate expansion of tidal creeks and creek bank erosion in multiple areas. The influence of S. reticulatum bioturbation on sediment erodibility has not yet been quantified, due to difficulties involved in measuring the processes in a field setting. In this study, we used a laboratory flume to examine the effects of burrowing by common marsh crab species S. reticulatum and Uca pugnax on sediment surface roughness and erodibility. Measurements and observations of surface elevation, flow velocities, and sediment movement indicate that burrowing and feeding by S. reticulatum , and to a lesser extent, Uca pugnax, increase surface roughness and decrease the threshold velocities and shear stresses required for sediment erosion. Erosion associated with observed burrowing is of a similar magnitude to mean annual marsh surface accumulation, and, consequently, this mechanism for sediment loss in heavily burrowed areas has the potential to produce large-scale morphological changes. Ecological engineering, Coastal setting, Salt marsh, Geomorphological aspects, Soil erosion. USA, Texas, Galveston. • We determine the impact of Sesarma reticulatum and Uca pugnax on erosion thresholds. • S. reticulatum increase surface roughness, more so than other crab species. • Crab burrowing decreases velocity and shear stress thresholds needed for erosion. • Extensive burrowing by S. reticulatum facilitates headward creek erosion and marsh landscape evolution. [ABSTRACT FROM AUTHOR]