Effects of the burrowing activity by crabs on soil environment dominated by Salix subfragils in estuarine wetland

Background/Question/Methods

Estuarine wetland is a transition zone where fresh and saline water meet together. It provides habitats for a wide variety of plants and animals and has high levels of primary productivity and biodiversity. The sesarmine crab, Sesarma dehaani thrives in the Janghang estuarine wetland where a tidal willow forest dominated by Salix subfragils exists. In general, the sesarmine crab is known to be closely related with the primary productivity of S. subfragils communities. However, little is known about the effects of crab burrowing activity on the rhizosphere soil environment of S. subfragils. We conducted a field study to determine if there is any influence of burrowing activity by crabs on the physicochemical properties of rhizosphere and bulk soil in S. subfragils communities. We established 2 x 2 m plots with five replicates in the upper brackish region of S. subfragils communities, and soil samples were taken two times in both rhizosphere and bulk soil from July 2013 through November 2013. Soil samples were additionally differentiated according to the presence or absence of the crab. Physicochemical properties of soil were measured at the depth of 5 cm, 20 cm, and 30 cm in each plot.

Results/Conclusions

We found several significant differences in the measured edaphic factors between rhizophere and bulk soil. There was a marked difference in the number of crab holes between two regions, more crab holes found in the bulk soil. Soil water content increased with the increasing depth in bulk soil compared to the rhizosphere soil and significant differences were found at the depth of 30 cm (p < .05). Higher soil organic matter and electronic conductivity were observed in bulk soil than in rhizosphere soil. Available phosphorus concentrations were also higher in bulk soil (p < .001) but soil pH was relatively lower in bulk soil. These results indicate that burrowing activity of crabs may be affected by soil nutrients and the presence of S. subfragils may be positively associated with the crab activity. Further study is needed to ascertain the possible relationship between S. subfragils communities and the sesarmine crab S. dehaaniin more detail.