Although crabs are effective indicator species for evaluating the health of estuarine environments, the relationship between crab communities and environmental conditions in temperate river estuaries is poorly investigated. This study aimed to clarify the physicochemical factors that affect crab fauna in temperate areas, as well as classify and characterize habitat based on the similarity of crab fauna. Data of crab fauna and physicochemical environmental factors were collected at 199 sites in two temperate rivers. These survey sites were spatially arranged to cover the estuarine zone (i.e., tidal freshwater to polyhaline water) and the intertidal zone (i.e., the high tide to low tide line). The result of a direct gradient analysis showed that salinity and median particle size, in particular, affected crab fauna. Moreover, the survey sites were classified into seven groups based on the similarity of crab fauna, which were modeled with moderate accuracy using three variables: salinity, elevation, and percentage of silt. From these variables, we were able to identify seven different habitat types: salt marshes covered with fine or coarse sediment, upstream zones with gravelly sediment, intermediate zones between salt marshes and tidal flats, sand tidal flats with scattered hard structures, monotonous sand flats, and mud flats. Our findings suggest that maintaining the salinity gradient and diversity of sediment grain size is necessary to conserve crab species diversity in temperate river estuaries. Effective ecosystem conservation in these areas needs to take into account the physicochemical conditions in the seven identified habitat types.

中文翻译：

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基于濑户内海温带河口潮间带蟹类动物的栖息地特征

尽管螃蟹是评估河口环境健康的有效指示物种，但对温带河口螃蟹群落与环境条件之间关系的研究却很少。本研究旨在阐明影响温带地区蟹类动物的理化因素，并基于蟹类动物的相似性对生境进行分类和表征。在两条温带河流的199个地点收集了蟹类动物和理化环境因素的数据。这些调查地点在空间上布置成覆盖河口区（即，潮汐淡水至多卤水）和潮间带（即，高潮至低潮线）。直接梯度分析的结果表明，盐度和中值粒径尤其会影响螃蟹的动物区系。此外，根据蟹类动物的相似性，将调查地点分为七个组，并使用三个变量（盐度，海拔和淤泥百分比）以中等准确度进行建模。从这些变量中，我们能够识别出七种不同的生境类型：覆盖有细小或粗大沉积物的盐沼，具有砾石沉积物的上游区域，盐沼与潮滩之间的中间区域，具有分散的硬结构的潮滩，单调的沙滩，和泥滩。我们的发现表明，保持盐度梯度和沉积物粒度的多样性对于保护温带河口蟹的物种多样性是必要的。在这些地区进行有效的生态系统保护需要考虑到七种已确定栖息地类型的物理化学条件。