Effects of reduced salinity caused by reclamation on population and physiological characteristics of the sesarmid crab Chiromantes dehaani.

Reduced salinity is a major factor that causes macrobenthic degradation in reclaimed wetlands. We investigated populations of the sesarmid crab Chiromantes dehaani in reclaimed and natural wetlands. Then, in the laboratory, we exposed male and female crabs to four salinity levels (0, 6, 12 and 18) for 96 h to analyse the effects of reduced salinity on osmoregulatory enzyme activities in the posterior gills and digestive and immune enzyme activities in the hepatopancreas of C. dehaani. The results revealed a significant positive correlation between the number of crabs and salinity. In the laboratory, we found that the isosmotic point of C. dehaani was close to 16 ppt. The crabs showed strong hyper-osmotic regulation when exposed to 0-6 ppt salinities. Moreover, in this salinity range, amylase activities were significantly inhibited. Under low-salinity stress, the immune enzyme activities were significantly activated. However, phenoloxidase and lysozyme activities were inhibited in the freshwater environment. The male and female crabs showed no significant differences in most of the enzyme activities. Thus, reduced salinity can adversely affect the digestive and immune functions of C. dehaani, which may cause population degradation in reclaimed wetlands. Our findings can provide new insights into the effects of reclamation on macrobenthos.