The effects of burrowing of Helice tridens (De Haan) on the soil of a salt-marsh habitat

The physical and chemical effects of the burrowing activity of the mud crab Helice tridens (De Haan) on the soil of a salt-marsh habitat were investigated. Soil-turnover rate caused by burrowing activity was found to be ≈ 3% of the soil from the surface to a depth of 40 cm every day during the summer. The vertical distributions of leaf and stem fragments of the salt-marsh plant Phragmites australis (Trin.) and the vertical distribution of ammonium N concentration in the soil were also investigated. At locations in the marsh where there were many large burrows, numerous leaf and stem fragments were recognized in the soil, while in areas in the marsh containing only a few small burrows these fragments were scanty. The soil depths at which leaf and stem fragments were abundant, corresponded to the depths of the burrows. These results show that mud crabs bury fallen plant fragments in the soil by their burrowing activity. Ammonium N in the soil was also abundant at locations in the marsh where there were many burrows, indicating that organic matter, such as fallen leaves and stems, may be decomposed to inorganic nutrients which are useful to the salt-marsh plants.