RESULTS
Crab Excavation and Burrow Mimic Deposition of Soil Four parameters were used to characterize the soil excavating–depositing processes driven by crabs,that is, excavation, deposition, deposition efficiency,and net transport. The deposition efficiency was the amount of deposited soil per unit volume of burrow; and the net transport was the difference between the amount of soil excavated by crabs and that deposited into burrow. Habitat type, duration of high tide, and burrow or burrow mimic diameter all had significant effects on the four parameters. Soils excavated, deposited into burrow mimics, and net transported to the surface increased with the increasing diameter of burrows or burrow mimics, but deposition efficiency decreased with increasing burrow or burrow mimic diameter (Figure 1). The four parameters all increased with increasing duration of high tide (Figure 1). Because crab excavation exceeded burrow mimic deposition, excavating–depositing processes resulted in net transport of soil to the marsh surface. Furthermore, the values of these parameters for mudflats were significantly higher than those for Phragmites and Spartina marshes. The soil excavated by crabs was positively correlated with burrow diameter (Figure 2A) and soil deposited into burrow mimics (Figure 2B) in both mudflats and Phragmites and Spartina marshes, and the regression slopes for mudflats were significantly greater than those for Phragmites and Spartina marshes.