Project Summary

Researchers manipulated densities of the invasive snail Littorina littorea at two sites, one in the Little River estuary and another in the Webhannet River estuary, to investigate the effect of grazing on plant production and sediment accumulation. They found that under more stressful conditions for saltmarsh cordgrass (Spartina alterniflora) – poor drainage or greater flooding, for example – the impact of snail grazing on biomass becomes apparent: Where snails eat cordgrass faster than it can grow back, less cordgrass is available to capture sediment and the marsh surface does not build up as quickly. In contrast, the impact of snails is not significant under more favorable conditions for cordgrass.

Management Message

Physical conditions at a given salt marsh site may influence the susceptibility of Spartina alterniflora to grazing pressure by the invasive snail Littorina littorea. Anthropogenic impacts, such as sea-level rise, could further stress saltmarsh plants, leaving them increasingly susceptible to herbivory.

Principal Investigators

• Megan Tyrrell, Wells National Estuarine Research Reserve
• Michele Dionne, Wells National Estuarine Research Reserve

Project Period

2004-2005

Resulting Publications & Presentations

1. Tyrrell, M.C., Dionne, M., and Edgerly, J.A. 2008. Physical factors mediate effects of grazing by a non-indigenous snail species on saltmarsh cordgrass (Spartina alterniflora) in New England marshes. ICES Journal of Marine Science 65:746–752.
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2. Tyrrell, M., and M. Dionne. 2007. Physical factors mediate effects of grazing by a nonindigenous snail species on salt marsh cordgrass, Spartina alterniflora, in northeastern salt marshes. Abstract, Fifth International Conference on Marine Bioinvasions. Massachusetts Institute of Technology, Cambridge, MA. 138pp.