Estimates of mortality in sandy beach populations of <i>Haustorioides japonicus</i> (Amphipoda: Crustacea) and <i>Excirolana chiltoni</i> (Isopoda: Crustacea) during winter storm seasons

Abstract

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 coefficient, 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.

Cross‐shore distributions of peracarid crustaceans after changes in beach morphology: The importance of suction as a key geoenvironmental variable

“…Application of the simple Poisson GLM for E. chiltoni indicates its overall low density in both sites, and demonstrates that suction has a consistently larger effect than the other geoenvironment variables and other not-measured factors, such as daily weather or microclimate produced by stranding debris, which may be included in the random date factor. The date factor should also involve temporal factors such as daily swash conditions or seasonal changes of the abundance (Takada et al, 2019).…”

“…On the Japan Sea coast, East Asian monsoons-induced northern winds are predominant in autumn and winter seasons. These monsoonal storms with heavy waves frequently give rise to intense morphological changes in sandy beaches (Mitsuta, Fujii, & Tsukamoto, 1983;Nagamura, 2000) and influence the abundance of H. japonicus and E. chiltoni (Takada et al, 2019).…”