Spatial Ecology of Fiddler Crabs,Uca pugnax, in Southern New England Salt Marsh Landscapes: Potential Habitat Expansion in Relation to Salt Marsh Change

Abstract

The spatial distribution of the fiddler crab Uca pugnax (Atlantic Marsh Fiddler Crab) in relation to salt marsh patch structure was investigated along the central Connecticut coast of Long Island Sound. Salt marsh landscape structure at the study sites exhibit characteristics consistent with changes noted in other systems along the US Atlantic coast over the last several decades, including significant seaward erosion, encroachment of low-marsh plants into high marsh, changing composition of high-marsh plant patch structure, and marsh dieback and drowning. Our objective was to determine whether the spatial patterns of U. pugnax inhabiting these systems differed from those previously reported for southern New England in light of these characteristics. Densities of crab burrows were highest in low-marsh patches of Spartina alterniflora (Atlantic Smooth Cordgrass) and unvegetated muds along tidal creek banks and mosquito ditches. Seaward-eroding low-marsh areas were generally devoid of live crabs and burrows. Crab-burrow densities varied across the complex patch mosaics in high-marsh areas. Burrow densities were generally low in the extensive short S. alterniflora patches that comprised much of the high-marsh area at several sites. However, high burrow densities, equivalent to low-marsh densities, were found in certain high-marsh patch types and upland transition zones. These included patches of Spartina patens (Marsh Hay Cordgrass), Distichils Spicata (Desert Salt Grass), and mixes of these, and particularly in S. patens patches wholly or partly comprised of hummocks of vegetation surrounded by bare sediment. At several sites, burrow densities were high in upland transition zone patches of Phragmites australis (Common Reed). As such, crab-burrow distributions were highly variable at local, within-marsh system spatial scales. Live U. pugnax were found regularly in all patch types on all marshes. Our results indicate a much broader distribution of U. pugnax at relatively high densities across southern New England marsh landscapes than previously reported. This finding may represent a case of habitat expansion in response to salt marsh change, likely due to sea-level rise and other factors, creating high-marsh habitats in a variety of patch types that can support resident populations of fiddler crabs. Such an expansion of a dominant salt marsh species, which can significantly affect ecosystem dynamics, may potentially increase the complexity of current salt marsh change patterns and dynamics along southern New England coastlines.