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.