Universality of the linkage between geoenvironment and the distributions of three Haustorioides amphipods: H. Japonicus, H. Munsterhjelmi, and H. Koreanus

Abstract

It is known that suction, namely, the tension of moisture in sediments, governs the distribution of the sandy beach amphipod Haustorioides japonicus, which occurs on the intertidal zones of open sandy beaches. Against this background, field studies were conducted to investigate whether there is a universal linkage between the suction and the distributions of three Haustorioides species, H. japonicus, H. munsterhjelmi, and H. koreanus, and to clarify the relationship between the distribution of these three species on shores and the variation in suction associated with the tide-induced variation in groundwater level. The study sites were as follows: Maze and Gokahama beaches, located on the coast of the Sea of Japan in Honshu, Japan and Tsuyazaki beach on the coast of the Genkai Sea in Kyushu, Japan for H. japonicus; Shari beach in Hokkaido, Japan for H. munsterhjelmi; and Samyang beach on Jeju Island, South Korea for H. koreanus. The field sites had different tidal ranges, from 0.2 to 2.81 m. The obtained results showed that the suction governed the variations of the habitat geophysical environments (degree of saturation, sediment compaction, water content, and sediment hardness) of surficial sediments in sandy beaches, and the distributions of the three Haustorioides species are associated with particular suctions, irrespective of the differences among the three Haustorioides species, the differences in tidal ranges, and the variations in tidal level. In addition, the tidal migrations of H. japonicus and H. munsterhjelmi were caused by shifts in their suitable zones for burrowing.