Effects of Deposit-Feeder Activity on Bacterial Production and Abundance in Profundal Lake Sediment

Abstract

Effects of the amphipod Monoporeia affinis, the oligochaete Tubifex tubifex and the chironomid Chironomus riparius on the production ([³H]-thymidine incorporation) and abundance (acridine orange direct counts) of sediment bacteria were studied in a series of microcosm experiments. Measurements were performed on the visually distinct sediment zonation generated by oxygen penetration and influenced by deposit-feeder activity. All three species at higher densities caused an increase in the depth of the light-colored surficial sediment layer in the microcosms. Bacterial production in surficial sediment increased by factors as high as 3.2× (Monoporeia experiment), 1.4× (Tubifex experiment), and 4.4× (Chironomus experiment) compared with controls. Physical disturbance of sediment through invertebrate activity was concluded to be the main causal mechanism for increases in bacterial production. Changes in bacterial abundance appeared to be zoobenthos species-specific, reflecting differences in feeding and/or foraging behavior of the animals. Bacterial abundance was negatively affected by mechanical stirring and by the activity of Tubifex tubifex, a subsurface deposit-feeder known to gain a large proportion of its energy demand from sediment bacteria. Monoporeia affinis and Chironomus riparius did not affect bacterial abundance; apparently their surficial feeding activity resulted in a compensation of bacterial losses. In subsurface sediment layers neither bacterial abundance nor production was affected by any of the three species.