Comparison and combination of selective grazing on natural seston by benthic bivalves (Hyriopsis cumingii) and pelagic fish (Hypophthalmichthys molitrix).

Biomanipulation of filter-feeding bivalves or fish can serve as complementary measures to zooplankton manipulation approach in lakes dominated by large-sized algae. A laboratory grazing experiment was conducted to compare the selective grazing of benthic bivalves (Hyriopsis cumingii) and planktivorous fish (silver carp) on particle size and algae species. Their combination grazing effects were also detected. The results showed that the clearance rates of silver carp were higher than that of H. cumingii, and that silver carp preferred particles in the 30-50 and 50-100 μm size fraction whereas H. cumingii did not show a significant selective grazing on seston size. Furthermore, the differences between the selective grazing of H. cumingii and silver carp on algae species were detected. Some algae species, which had not been digested well by silver carp, were not detected in H. cumingii's pseudofeces. Similarly, some algal species in the pseudofeces of bivalves were not detected in the feces of fish. Moreover, the combined clearance rates of H. cumingii and silver carp (ranging from 12.14 to 95.99 mL g DW-1 h-1) were higher than that of single filter feeder (0.47 to 10.18 mL g DW-1 h-1). We suggest therefore that when using biomanipulation measures to control large-sized algal overgrowth, a combination of different filter feeders may be a better way considering their collaborative grazing in both particle size and algae species selectivity.