CHARACTERISTICS OF ZEBRA MUSSEL (DREISSENA-POLYMORPHA) BIODEPOSITS INA TIDAL FRESH-WATER ESTUARY

Zebra mussels are now a major component of the benthos in the tidal fr eshwater Hudson River. Their filtering activity has had a wide range o f ecosystem-level effects. Zebra mussel biodeposits (feces and pseudof eces) were sampled in in situ chambers containing mussels attached to artificial substrates. The biodeposits collected were analyzed for org anic matter (OM), chlorophyll-a, phaeopigments, C, N, bacterial cell d ensities, and bacterial production rates. Relative to control sediment s (sediments passively collecting in the chambers), biodeposits were s ignificantly enriched in all measures except bacterial cell densities. Biodeposits were estimated to contain 9.5 % OM and 3.9 % live algae b y weight, while values in passive deposits were 7.8 % and 1.1 %, respe ctively. The C:N ratio of biodeposits was estimated at 8.3, and bacter ial production was estimated at 14.6 x 10(7) cells gOM(-1) h(-1), whil e passive deposit values were 9.8 and 7.4 x 10(7) cells gOM(-1) h(-1), respectively. When subjected to a range of mixing energies, biodeposi t mixtures (feces, pseudofeces and passive deposits) were resuspended at a bed stress that was approximately 50 % lower than the bed stress required to resuspend the passive deposits. Although biodeposits were shown to be enriched in the above measures, their resuspension by wate r currents in a system like the tidal freshwater Hudson River will red uce their residence time at the river bottom, possibly reducing their ecological impact on the benthos.