The distribution and abundance of Helice tridens (De Haan) burrows and substratum conditions in a northeastern Japan salt marsh (Crustacea: Brachyura)

The effects of the physical condition of the substratum on the distribution and abundance of mud-crab burrows were investigated. In the salt-marsh habitats studied, where burrows were abundant, there was a high proportion of silt-clay. In such conditions, the diameters of openings and the depths of the burrows were greater than those when the relative proportion of silt-clay was low. In the laboratory, it was found that with a low proportion of clay, mud-crabs did not dig burrows when the water content was high and thus equivalent to that in the marsh. When the proportion of silt-clay was low, the larger mud-crabs did not make burrows at the depth of the water table in the marsh, because the layer above the water table was too thin to allow construction of the burrow. The field observations could thus be explained by the results of experiments showing that the depth of the burrows was controlled by the depth of the water table and the relative proportion of silt-clay in the substratum.