SIGNATURE WORK
CONFERENCE & EXHIBITION 2022

Salt marshes are a valuable biogenic habitat that provide numerous ecosystem services such as carbon storage and shore stabilization, to name a few. These habitats can also face environmental stressors such as nutrient limitation. Both nutrient enrichment and mutualistic interactions with bivalves can have impacts on marsh primary production, but little is known about the effects of these two factors on plant biomass, associated animal communities, and sediment accretion. To address this intellectual void, we conducted a fully factorial experiment crossing nutrient addition with ribbed mussel (Geukensia demissa) density over a 6-month growth season in a North Carolina, USA salt marsh. We did not find interactive effects of nutrient additions and mussel density. However, strong main effects were observed. Both nutrient and ribbed mussel addition led to increases in marsh (Spartina alterniflora) plant biomass (p>0.0001), plant flowering (p>0.0001), grazer scars (p=0.0007), and abundance of detritivores, grazers, and predators. The effects of nutrients and mussel addition contrasted, however, in their impacts on sediment accretion and redox potential. Nutrients had no effect on redox potential, sediment accretion and marsh elevation, whereas mussel addition increased marsh elevation by nearly 4cm (p>0.0001) and increased redox potential (p>0.0001). These results confirm past studies showing bottom-up control of plant and animal abundance in salt marsh communities and highlight that mutualistic species interactions have the potential to play a key role in the ability of marshes to keep pace with sea-level rise.