Population scarcity of an estuarine crab (Chiromantes dehaani) caused by intertidal reclamation from the perspective of reduced salinity

Decreased salinity is one of the main abiotic factors causing macrobenthic degradation in reclaimed intertidal wetlands. However, our knowledge of the mechanism(s) underpinning this degradation remains surprisingly scanty. To fill this gap, here we used the crab Chiromantes dehaani as a study subject. First, we investigated differences between C. dehaani populations in fully- and semi-enclosed wetlands in 2018. Then, in controlled experiments, we exposed female C. dehaani to freshwater (salinity of 0) and two salinity levels (3 and 12) for 12, 24, and 48 days to explore the effects of reduced salinity on the osmoregulation and lipid materials of C. dehaani. Then, the surviving crabs mated with mature male crabs, and the spawning rate, fecundity, and abortion rate of female crabs quantified to reveal the effects of lower salinity on reproduction in this species. Our results revealed that no crabs could be found in the fully-enclosed zone, where the salinity level closely matched that of freshwater. In controlled experiments, the C. dehaani showed the ability of osmoregulation under freshwater condition, but it consumed more lipid materials to maintain stable osmotic pressure. Moreover, the ovary development of C. dehaani was significantly inhibited in the freshwater group, which resulted in no spawning crabs. In contrast, the breeding success of female crabs in salinities of 3 and 12 reached 90.5 ± 4.8% and 79.4 ± 6.9%, respectively. The abortion rate of embryos increased significantly after spawning crabs were exposed to the freshwater environment. Collectively, the reproduction barriers caused by salinity's decrease may be a critical causal factor driving the scarcity of C. dehaani population in reclaimed wetlands of Yangtze estuary. These findings are expected to provide new insights into the effects of reclamation on macrobenthos.