Cross-shore distributions of peracarid crustaceans after changes in beach morphology: The importance of suction as a key geoenvironmental variable

摘要

Recently, it has been shown that suction, which means the tension of moisture in sediments, is responsible for the distribution limits of the amphipodsHaustorioides japonicusandTrinorchestia trinitatisand the isopodExcirolana chiltoni. Such effects take place through three distinctive suction-induced mechanisms, associated with burrowing, physiology and the stability of burrows. Based on this background, in this study, we investigated storm-induced morphological changes in beach profiles and the associated variations in geoenvironments, namely the suction, the degree of saturation, water content and sediment hardness, of the sandy beach habitats. The associated changes in cross-shore distributions of the three peracarid crustaceans were also investigated. Field studies were carried out before and after monsoonal storms at two sandy beaches, Maze and Gokahama, located on the Japan Sea coast in Niigata Prefecture, Japan. The results showed that the suction-induced variations of the geophysical environments were universal, irrespective of the storm-induced morphological changes in the beach profiles. In addition, there were distinct changes in the cross-shore distributions of the peracarid crustacean populations, associated with the storm-induced morphological changes. The variations in the developed suction consistently and quantitatively accounted for these distinct changes in the cross-shore distributions of the peracarid crustaceans, associated with the event-induced morphological changes. Hence, suction played a crucial role as a key geoenvironmental variable in determining the distribution changes of the three peracarid crustaceans studied, even following the event-induced morphological changes of the beach profiles.