Burrowing,root mat density,and the distribution of fiddler crabs in the eastern United States

This paper discusses the distribution of two species of fiddler crabs across an estuary. The possibility that sediment size, physical factors (or micro-climate), or food limitation could lead to the observed distributions is discussed, and evidence is presented to show that these factors probably play a minor rôle in controlling the distribution of Uca pugnax (Smith) and U. minax (Le Conte) across an estuary. The results show that the best correlate of the dominant species of Uca in a particular habitat is the density of the root mat of that area. A series of experiments showed that variations in the abundance of large U. pugnax at two tide levels in a marsh very closely parallel the ability of U. pugnax to burrow in substrata taken from those same two areas of the marsh. These two areas have significant differences in density of the root mat.