Habitat zonation of the sand-burrowing mysids (Archaeomysis vulgaris, Archaeomysis japonica and liella ohshimai), and diel and tidal distribution of dominant Archaeomysis vulgaris, in an intermediate sandy beach at Fukiagehama, Kagoshima Prefecture, southern Japan

Abstract

Distribution patterns of the three species of sand-burrowing mysids, Archaeomysis vulgaris, Archaeomysis japonica and liella ohshimai were investigated, and also the diel and tidal distribution patterns of the dominant mysid A. vulgaris were investigated in the surf zone of an exposed and mesotidal sandy beach at Fukiagehama, Kagoshima Prefecture, southern Japan. The morphodynamic state of the beach was an intermediate type with a low-tide terrace or ridge/runnel. Habitat zonation was recognized among the three species during the entire study period (May and October of 2002 and 2003). A. vulgaris occurred from the high-water shoreline to the low-water shoreline during the daytime, whereas A. japonica was observed off the low-water shoreline and I. ohshimai was found far from the longshore bar. Habitats of A. vulgaris shifted along the beach slope, depending on the tidal changes at the shoreline. However, at low water in May of 2002 and 2003, most individuals of A. vulgaris were distributed in the intertidal runnel and on the lowtide terrace, rather than off the low-water shoreline. A. vulgaris had the highest population density of the three species, and fluctuations in its total mean density in the surf zone were estimated at each tide in May of 2003. These ranged from 2,956 indiv. m^-2 at low water at night to 172 indiv. m^-2 at middle water during the daytime. Distribution patterns characteristic of A. vulgaris are ecologically interpreted in relation to beach morphology, water flow regimes in the surf zone, and avoidance of fish-predation pressure.