Diel and Tidal Migrations and Predator-prey Relationships of Macrobenthic Animals in Intertidal Sandy Beaches of Sendai Bay, Northern Japan

Abstract

Abstract: We describe predator-prey relationships related to diel and tidal migrations based on observations of the distributions of macrobenthic animals over24hours along sandy beach slopes in two locations of Sendai Bay, northern Japan. The macrobenthic communities were largely comprised of Excirolana chiltoni(Isopoda: Cirolanidae), Haustorioides japonicus(Amphipoda: Dogielinotidae), and Archaeomysis kokuboi and A. vulgaris(Mysidacea: Gastrosaccinae). Excirolana chiltoni occurred in the swash zone at high tide and its distribution did not shift with the tidal cycle. On the other hand, H. japonicus, A. kokuboi, and A. vulgaris, located in the swash zone, shifted with the tides. Their distributions overlapped with that of E. chiltoni only at high tide. Gut content analysis suggested that A. kokuboi and A. vulgaris mainly fed on copepods at night, and that H. japonicus mainly fed on particulate detritus; E. chiltoni mainly fed on the mysidaceans, H. japonicus, and stranded carrion. These facts suggest that a food chain starts with detritus and copepods in the swash zone and the sublittoral zone, passes through H. japonicus or mysidaceans in the swash zone, and leads finally to E. chiltoni in the upper littoral zone. Judging from the fact that the overlap of the distributions of macrobenthic animals was formed by their tidal and diel migrations along the beach slope, it can be concluded that the predator-prey relationships in sandy-beach communities are maintained by the tidal and diel migrations of macrobenthic animals.