Inter- and intra-specific differences in filtering activities between two unionids, Anodonta woodiana and Unio douglasiae, in ambient eutrophic lake waters

Inter-specific and intra-specific differences in the filtering activities of two unionid bivalves, Unio douglasiae and Anodonta woodiana, which thrive in small agricultural canals, were compared using a flow-through chamber system of ambient eutrophic lake water. The mean filtration rates (FRs) of these two species, size-matched for similar shell length, were not significantly different (t-test, t = 0.024, P = 0.981), whereas there were significant differences in the FRs between mussels of different ages (t-test, t = 5.137, P = 0.001), different densities (t-test, t = 8.297, P < 0.0001), and different currents (t-test, t = 3.898, P = 0.005). The FRs of A. woodiana increased significantly more with higher temperatures in younger mussels (P < 0.01, maximum FR = 0.352 ± 0.157 L/h at 13.5–20.4 °C) than in adults. However, the mortality of the mussels was comparatively higher in younger mussels due to a low tolerance to ammonia. Correlation coefficients and PCA results collectively indicate that the two dominant unionid mussels in the canal had a strong relationship with the seston level in the lake (turbidity, suspended solids and chlorophyll-a), resulting in a higher FR, pseudo-faeces production, and ammonia tolerance and a lower mortality. In addition, the validation of the biomanipulation used in the mussel-controlled system is discussed in an effort to improve the water quality of eutrophic lakes and streams and the conservation of the benthic mussel community.