Burrow Distributions and Population Estimates for the Fiddler Crabs Uca spinicarpa and Uca longisignalis in a Gulf of Mexico Salt Marsh

Abstract

The distribution of fiddler crab (Uca spinicarpa andU. longisignalis) burrows in coastal marsh habitats is described, and the influence of substratum characteristics on the distributions of each is examined. Burrow densities were higher in vegetated areas than in sparsely vegetated and nonvegetated areas. Elevation and landward distance from shoreline (water's edge) also co-varied with burrow densities along transects. Burrow aperture diameters and burrow numbers m−2 exhibited seasonal variations for both species ofUca. The depth of burrows increased with increased distance from the water's edge (approximate mean sea level) along transects into the marsh. A significant correlation between burrow aperture diameter and carapace width of the inhabitant enabled subsequent estimates of size and biomass in populations. Mean burrow densities forU. longisignalis ranged from a high of 182 m−2 in September 1992 to a low of 26 m−2 in May–June 1992. Mean burrow densities forU. spinicarpa ranged from a high of 46 m−2 in March April 1993 to a low of 29 m−2 in May–June 1992. Estimates of mean biomass ranged from 17.6 g AFDW m−2 to 13.2 g AFDW m−2 for aU. longisignalis-dominated site and from 6.5 g AFDW m−2 to 4.9 g AFDW m−2 for aU. spinicarpa dominated site. Field observations and laboratory soil-choice tests demonstrated that, in mixed populations,U. spinicarpa preferred to burrow in substrates of higher percent clay than didU. longisignalis.