What Is the Role of Ecosystem Engineers in New England Salt Marshes? A Mesocosm Study of the Fiddler Crab and the Purple Marsh Crab

The services and functions provided by coastal wetlands are numerous and influenced by factors ranging from climate and tidal regime to ecosystem engineers and anthropogenic modifications. In New England salt marshes, fiddler crabs and purple marsh crabs are cooccurring species that are among the most conspicuous burrowing macroinvertebrates in the region. Both are known to influence salt marsh ecosystem functions through their burrowing and feeding behavior, but the ways in which they regulate specific properties, individually and together, is unclear. Using an ex situ mesocosm study, I manipulated the presence of fiddler crabs and purple marsh crabs in order to evaluate their impact on several soil properties and aboveground biomass. Results show that, contrary to previous studies, the fiddler crab had little impact while the purple marsh crab altered soil quality with positive implications for plant growth. This suggests that the purple marsh crab, known to be a voracious consumer of marsh vegetation, may play a much more nuanced role in the maintenance of plant growth than previously thought. Additional ex situ studies should be done to further delineate the impact of these two species.