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.

盐度降低是造成退潮潮间带湿地大型底栖动物退化的主要非生物因素之一。但是，我们对导致这种降解的机理的知识仍然令人惊讶。为了填补这一空白，在这里我们以螃蟹Chiromantes dehaani为研究对象。首先，我们调查了2018年全封闭和半封闭湿地中C. dehaani种群之间的差异。然后，在对照实验中，我们将雌性C. dehaani暴露于淡水（盐度为0）和两个盐度水平（3和12）下，第12、24和48天探讨盐度降低对C. dehaani渗透调节和脂质物质的影响。然后，将存活的螃蟹与成熟的雄性螃蟹交配，对雌性螃蟹的产卵率，繁殖力和流产率进行量化，以揭示盐度较低对该物种繁殖的影响。我们的结果表明，在完全封闭的区域中没有发现任何螃蟹，那里的盐度水平与淡水非常接近。在对照实验中，C. dehaani表明渗透调节的能力淡水条件下，但它消耗了脂质材料以维持稳定的渗透压。此外，C。dehaani的卵巢发育在淡水组中被显着抑制，因此没有产卵蟹。相反，在3和12的盐度下，雌蟹的繁殖成功率分别达到90.5±4.8％和79.4±6.9％。产卵蟹暴露于淡水环境后，胚胎的流产率显着增加。总体而言，盐度降低引起的繁殖障碍可能是导致长江口开垦湿地中C. dehaani种群稀缺的重要原因。这些发现有望为填海对大型底栖动物的影响提供新的见解。