Current reproductive situation in a reduced population of juvenile mussels (Unio douglasiae) at a eutrophic lake

Abstract

 Unionid mussels play an important role in the cycling and removal of suspended substances from freshwater ecosystems. Unfortunately, their populations are declining worldwide. Although the mechanism for that is unclear, one possible reason may be a reproductive disturbance, because previous studies have reported that the numbers of young and juvenile mussels are few. In this study, we focused on Unio douglasiae nipponensis, which inhabit Lake Hachiro in Akita Prefecture; and we identified when and whether larvae were released by parent mussels. Host fish were also identified. As a result, we discovered that larvae were released from June to July, and that the host fish were gobies (Tridentiger brevispinis). However, juvenile mussels were rare in that location. There is another possibility for unionid mussel reduction, such as the muddy lake bed in Hachiro. To conserve Unio douglasiae nipponensis, further surveys are needed.