Salt marshes are highly productive ecosystems which perform many valuable services including carbon sequestration, nutrient transformation, and mitigation of rough waters generated by storms. Coastal salt marshes currently face threats resulting from global climate change, including sea level rise (SLR). Coastal marshes have kept pace with historical SLR through elevation gain via sediment precipitation from tidal waters. In the coming century, sea level is expected to increase 5x-8x faster than the previous century. Since the rate of sedimentation is unlikely to increase with SLR, marshes are in danger of habitat loss via drowning and subsidence. The decomposing organisms in salt marsh sediments are essential to maintaining marsh plant health. The response of decomposing organisms to longer periods of inundation is unclear. To determine how the prokaryote and invertebrate communities may change in response to SLR, mesocosms were designed, which simulated different inundation intensities within the marsh. A gradient developed over the 10-month sampling period in which the most inundated sediments had significantly different communities than the driest sediments. The high inundation treatments were dominated by anaerobic prokaryotes and insect larvae, and sulfate reduction was the predominant decomposition processes. The ambient mesocosms (driest sediments) were dominated by aerobic prokaryotes and oligochaete worms. Aerobic processes such as leaf litter decay became the key decomposition processes in these sediments.