北限のマングローブ林周辺干潟におけるウミニナ類分布の季節変化

抄録

Four batillarid species ; Batillaria multiformis (Lischke, 1869), Cerithideopsilla djadjariensis (K. Martin, 1899), Cerithideopsilla cingulata (Gmelin, 1791) and Cerithidea rhizophorarum A. Adams, 1855, coexist on a tidal flat covered by a small mangrove forest in river mouth of the Atago river on southern Kyushu Island, Japan. This forest is dominated by Kandelia candel (L.) Druce and Hibiscus hamabo Sieb. et Zucc., which are the northern limit of mangrove distribution in the West Pacific. We investigated seasonal changes of the distributions and micro-habitat preferences of the four batillarid species to evaluate their possible niche segregation. Newly recruited juveniles (2-3 mm in shell width) of B. multiformis, C. djadjariensis and C. cingulata appeared from April to August, to June, and to May, respectively. No newly recruited juvenile of C. rhizophorarum was found in this study. However, adults and juveniles of C. rhizophorarum recruited before the year of this study was found in higher tidal zones than the other three species. The distributions of juveniles of four species, however, were limited to lower tidal zones. The result of desiccation-tolerance experiment showed that C. rhizophorarum has stronger tolerance than the other three species. This relatively high torelance likely allows C. rhizophorarum to climb up and hibernate on mangrove trees during winter.