Potential impact on bacteria of grazing by a macrofaunal deposit-feeder, and the fate of bacterial production

Bacterial biomass and production were compared to the carbon requirement and sediment processing capability of the deposit-feeding polychaete Euzonus mucronata (Treadwell) on a sand beach in Oregon, USA. Mean bacterial abundance ranged between sampling dates from 5.2 to 12.0 X 107 cells g-' sediment and mean biomass ranged from 1.5 to 3.4 pg C g-' sediment (0.36 to 0.84 g C m-2 to 15 cm depth). Daily bacterial production based on tritiated thymidme incorporation on 7 December 1982 is approximately 55 mg C m-2 d-'. The carbon requirement of E. mucronata, equal to the sum of annual production and respiratory loss of carbon, was 7.0 to 8.0 g C m-2 yr-l (19.3 to 21.9 mg C m-2 d-'). Although bacterial production exceeded the carbon requirement of E. mucronata, the low bacterial denslty limits direct uhhzation of bacterial carbon to <10% of the average daily carbon requirement of E. mucronata, despite its relatively high sediment-processing capability. Conversely, E. mucronata ingests