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Intertidal distribution of Haustorioides amphipods were studied in relation to the tidal fluctuation at four sandy beaches in Japan and Korea, to understand their behavioral responses to environment during tidal fluctuations. Presence or absence of Haustorioides individuals (including four species: H. japonicus, H. koreanus, H. munsterhjelmi, and H. nesogenes) were generally recorded at 2 m intervals from the drift line to the swash zone at various tidal conditions including high tides and low tides. Generalized linear mixed models demonstrated that the occurrence of Haustorioides amphipods at the sampling points were best described by a model with suction (the tension of moisture in the sediment) as an explanatory variable. Other environmental variables at the sampling points (slope angle, distance from the shoreline at the sampling time, and height from the sea level at the sampling time) were relatively poor predictors. The model showed that the probability occurrence of the amphipods was highest at the suction value of 0.76 kPa. Thus, the tidal migration behavior of these Haustorioides amphipods can be explained by suction dynamics rather than the swash conditions. This response was common to all four species and appears to be consistent over various tidal conditions. [ABSTRACT FROM AUTHOR]

Sandy beach habitats are mainly controlled by the physical environmental factors. This study investigated the effects of winter storms on populations of sandy beach infaunal peracarids. Two contrasting areas on the Japan Sea coast were selected: exposed sandy beaches in Niigata and protected sandy beaches in Sado. Regional differences in the mortality rate of two species of peracarids, Haustorioides japonicus and Excirolana chiltoni, were examined over two years, focusing on periods of high storm intensity (fall and winter) when sandy beach habitats are frequently disturbed. The results demonstrated that: (1) the mortality rate on the exposed beaches (Niigata) was significantly higher than that on the protected beaches (Sado); (2) the mortality rate in 2009-2010 was significantly higher than that in 2008-2009; and (3) the mortality rates were not significantly different between the two species. Sediment grain size, sorting coeffi- cient, and beach slope were not different between the two study areas. Dominant waves during the stormy seasons were from the northwest, to which the beaches in Niigata were directly exposed. Moreover, mean wave height was higher in 2009-2010 than in 2008-2009. Therefore, the variations in wave disturbances were herein considered to be the major cause of the mortality variations in the two species. According to the predicted scenarios of climate changes, wave intensification will likely increase in the future, therefore increasing the mortality and the potential risk of local extinctions of these sandy beach infaunal animals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Zonation has been a major focus of intertidal ecology. In general, sandy beaches are thought to have three zones (supralittoral, littoral, and sublittoral zones). In the present study, 41 areas of sandy beaches were surveyed along the Japan Sea coast of Honshu (from Aomori to Yamaguchi Prefectures) characterized by a small tidal range, large seasonal fluctuations in the mean tide level, and harsh wind-driven waves in winter, and the applicability of the three-zone scheme was examined. Overall, a total of 316 beach stations were surveyed, 28 taxonomic units were identified, and the most abundant species was the amphipod Haustorioides japonicus. The taxonomic units were grouped using multivariate techniques into a total of 7 assemblages, and the relationship of these assemblages to zonation was examined. Investigation of the indicator species of the 7 assemblages and their vertical position on the beaches showed that one assemblage corresponded to the supralittoral zone (indicators were talitrid amphipods and the isopod Tylos granuliferus). Another assemblage corresponded to the sublittoral zone, and the other five assemblages to the littoral zone. The assemblage of the sublittoral zone tended to disappear on the northern beaches, while one of the littoral assemblages whose indicators included a mysid species, Archaeomysis kokuboi, tended to occur on the northern beaches. Thus, the three-zone scheme can be applied to sandy beaches of the Japan Sea, but there are large variations among the beaches. [ABSTRACT FROM AUTHOR]