Fiddler crab-vegetation interactions in hypersaline habitats

Abiotic conditions often change ecological interactions. Studies in areas with low to moderate soil salinities have demonstrated a facultative mutualism between fiddler crabs and salt marsh vegetation. In these habitats, fiddler crab burrowing increases plant growth, and plant roots help support the walls of crab burrows. We looked for these interactions in hypersaline soils bordering unvegetated salt pans in a Georgia salt marsh. Crab burrows and vegetation cover were positively associated. Neither crab removals nor burrow additions demonstrated a positive effect of crabs on vegetation. However, both vegetation removals and the addition of an artificial canopy (suspended shadecloth) demonstrated a strong positive effect of vegetation on crab burrows. In contrast to previous studies, we found no evidence that plants supported burrow walls. Instead, crabs likely associate with vegetation to avoid predators. Our results caution against extrapolating experimental results between habitats with different abiotic conditions. (C) 1998 Elsevier Science B.V.