As part of a clarification of the response mechanisms of beach ground arthropods to the 2011 Tohoku-oki tsunami, a pit-fall trap survey was conducted in August and September 2012 and 2013 on four relatively flat sandy beaches in northern Tohoku region (i.e., northern Iwate to southern Aomori Prefecture) in Japan. At each beach surveyed, eight clean plastic cups with no baits were put for two days on each of the five beach zones (i.e., wrack, non-vegetated, short-herbaceous, tall-grass, and shrub zones). Among the ground arthropods in this study, we report the differences in susceptibility of two sandhoppers (Trinorchestiatrinitatis and T. longiramus), which dominate on the beaches and play an important role as prey for beach predators, to the tsunami, through monitoring their population dynamics. Although the abundance of the two species increased with time after the disturbance, T. trinitatis had a higher population growth rate than T. longiramus. In 2012, these two talitrid amphipods were collected mostly in the wrack zone, where the seaweed and driftwood accumulated, and on the non-vegetated zone near the shoreline, whereas they occurred in all beach zones in 2013. Since T. trinitatis burrows near the beach surface during its reproductive period in spring, this species might have suffered a large impact from the tsunami’s coastal erosion. On the other hand, our findings suggest that Trinorchestia species rapidly recolonize coastal regions in a short period of time (within a year), due to their reproductive ability and the accumulation of sea wrack, which provides food and habitat to these sandhoppers.
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