Distribution and life-history traits of Unionoid mussels in floodplain waterbodies of the Ishikari River

Despite of the importance of floodplain waterbodies for biodiversity and ecosystem services, human activities have degraded their quality as habitat for biological communities. Detailed understanding of life-history traits and population dynamics of organisms is crucial to the development and realization of effective management practices for the conservation of biodiversity. This study examined the distribution, reproductive traits, and host-fish utilizations of Unionoid mussels in floodplain waterbodies of the Ishikari River, northern Japan, and highlighted challenges in ecosystem management. Three target species exhibited the differences in habitat preferences, with Anemina arcaeformis（Heude, 1877）being disproportionately most abundant in marsh-type waterbodies. Two species, Sinanodonta lauta Martens, 1877 and Unio douglasiae nipponensis Martens, 1877, were gravid in summer（July and August）while A. arcaeformis was more gravid in fall and winter（October and November）. The low abundances of immature small individuals and the absence of parasitic attachments of mussel larvae to field-collected fish suggested the reduced levels of recent recruitments. The proliferations of invasive fish species such as Rhodeus ocellatus ocellatus, which comprised 30―70% of the total abundances of fish and were not suitable as host for the parasitic larvae of mussels, might be a possible cause of poor recruitment rates. Recognition of the diversity of waterbody types as a driver of species diversity, continued monitoring of population sizes and further elucidations of habitat quality as well as other aspects of life-history processes will contribute to improved ecosystem-based management of floodplain waterbodies in the Ishikari River.