Factors affecting distribution of freshwater shrimps and prawns in the Hiwasa River, southern central Japan

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Distribution of freshwater shrimps and prawns and its relationship with environmental factors were studied in the Hiwasa River, Tokushima Prefecture, southern central Japan, to provide information needed for conserving or propagating them more effectively. Eleven species of decapod crustaceans consisting of three palaemonids, six atyids, and two crabs were collected, of which eight species were diadromous. Results of canonical correspondence analysis showed that substrate coarseness in addition to conventional longitudinal variables largely affects overall decapod distribution. Differences in distribution patterns among amphidromous species were mainly explained by riverbank vegetation coverage and the two aforementioned variables. In contrast, distribution of a non-diadromous atyid, Neocaridina denticulata, was suggested to be determined by relative ease for them to resist flood in that habitat, rather than by longitudinal factors. These results insist on importance of coarse boulder bed and riverbank vegetation as shrimp and prawn habitats at reach scale. The range of Caridina typus within a river differed between the Japanese Archipelago and the Ryukyu Archipelago, and may be explained by limited low-temperature tolerance of this species. Incorporating these results and life history traits of the collected species, we propose a new classification system of distribution patterns for freshwater decapods on the Japanese Archipelago.
2012-12-20