Abstract
To detect factors affecting settlement, upward migration, and subsequent survival of diadromous organisms, the relationships between abundance of diadromous invertebrates (decapod crustaceans and a gastropod) and environmental features of various rivers (amount of flow and any artificial structures) was examined among 75 rivers in Fukuoka Prefecture, Japan. Field collection indicated that the shrimp Caridina leucosticta and the snail Clithon retropictus were more abundant in rivers with larger amounts of flow, while Caridina typus occurred only in rivers with smaller flows, suggesting interspecific differences in behaviors of settlement/ upward migration. Further, C. leucosticta and C. retropictus were more abundant in rivers with dams, and C. typus was more abundant in rivers without floodgates, probably due to apparent effects by multiple correlations between the existence/non-existence of dams and floodgates and the amount of flow of each river. Effects of artificiality of riverbed/riverside and the amounts of vegetation on the abundance of each diadromous species were considerably different among species: C. leucosticta was more abundant in rivers having natural riverbeds and a water's edge with abundant vegetation, while C. typus, E. japonica, and C. retropictus were abundant in rivers with artificial riverbeds or shore protections. This interspecific difference is considered to reflect differences in ecology/behavior in freshwater areas. Neocaridina denticulate, a non-diadromous shrimp, was abundant in pools above dams. To assess the effects of artificial structures on diadromous invertebrates, one needs to focus not only on the direct effects of the structures (intercept of migration routes, etc.) but also on the indirect ones due to changes in biological environments (competition, predation, etc.).
