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

Abstract

Recently, it has been shown that suction, which means the tension of moisture in sediments, is responsible for the distribution limits of the amphipods Haustorioides japonicus and Trinorchestia trinitatis and the isopod Excirolana 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.

Response to suction dynamics on intertidal distribution of <i>Haustorioides</i> amphipod species on East Asian sandy beaches during diurnal tidal changes

“…Because suction values dynamically changed along with the tidal changes (Yang et al 2019(Yang et al , 2020a, individuals of Haustorioides are thought to move their position to follow the zone of 0-2 kPa suction. Previous study also showed that H. japonicus kept their occurrence within the zone of 0-2 kPa suction both before and after storm induced morphological changes of sandy beaches (Yang et al 2020c). After storm induced beach morphological changes, it had been difficult to distinguish effects of passive movement of H. japonicus accompanied with sediment erosion and deposition on the beach or active movement following the spatial displacement of the zone of the specific suction (Yang et al 2020c).…”

“…Previous study also showed that H. japonicus kept their occurrence within the zone of 0-2 kPa suction both before and after storm induced morphological changes of sandy beaches (Yang et al 2020c). After storm induced beach morphological changes, it had been difficult to distinguish effects of passive movement of H. japonicus accompanied with sediment erosion and deposition on the beach or active movement following the spatial displacement of the zone of the specific suction (Yang et al 2020c). Regarding the change of the vertical distribution of Haustorioides amphipods, the present results suggest the possibility of active movement of individuals selecting a preferable zone indicated by suction.…”

“…This indicates an isophasic response of the amphipods to the tidal fluctuation instead of an isozonal behavior (Chelazzi 1990). This had been unclear in the previous studies done on microtidal sandy beaches (Sassa et al 2014, Yang et al 2020c). Isozonal behavior is observed in homing limpets on rocky shores (Iwasaki 1994) and grazing gastropods on a gently sloping boulder shore (Takada 2001).…”

“…A recent study on H. japonicus investigated the effects of storm-induced changes of beach morphology on their distribution on microtidal sandy beaches in Niigata, Japan (Yang et al 2020c). Although the horizontal position of H. japonicus changed on the beach according to the beach morphological change, it occurred within a zone of suction value between 0 and 2 kPa.…”