Predation and depth effects on abundance and size distribution of an invasive bivalve, the golden mussel Limnoperna fortunei, in a dam reservoir

We investigated the predation and depth effects on abundance and size distribution of an invasive freshwater bivalve, Limnoperna fortunei, post-larvae using screened (5-, 25-, and 50-mm mesh openings) and unscreened cages at three depths (6, 12, and 1 m above the bottom) in a dam reservoir, Lake Ohshio of Japan. The densities of L. fortunei on the unscreened cages were much lower than those of the 5-mm mesh screened cages at any depth. The predation rates estimated by dividing the density of the unscreened cage by that of the 5-mm mesh screened cage were 97.3% at 6 m depth, 96.6% at 12 m depth, and 95.8% at the bottom. Shell lengths of L. fortunei post-larvae were small on bottom cages, and their size distribution was significantly different from those at other depths. These results suggest that predation and depth affected the abundance and size distribution of L. fortunei in the lentic environment. The impact of L. fortunei invasion on the food web and the possibility of regulating their population by predation pressures are also discussed.