Virus-like particle distribution and abundance in sediments and overlying waters along eutrophication gradients in two subtropical estuaries

Viruses are recognized as ubiquitous components of marine ecosystems howeve r, there has been limited study of viral abundance and its ecological role in sediments. Viral abundance was determined in both the water column and s ediments of a eutrophic (Brisbane River/Moreton Bay; 27 degrees 25'S, 153 d egrees5'E) and oligotrophic (Noosa River, 26 degrees 15'S, 153 degrees0'E) estuary in subtropical Queensland, Australia. Viruses, bacteria, and microa lgae from both water column and extracted sediment samples were enumerated using SYBR Green I staining and epifluorescence microscopy. Sediment viral abundance ranged from 10(7) to 10(9) particles cm(-1) of sediment. bacteria l abundance ranged from 10(7) to 10(8) cells cm(-1) of sediment, and microa lgal abundance ranged from 10(4) to 10(5) cells cm(-1) sediment. Pelagic ab undances for all microorganisms were 10-1,000-fold lower than sediment abun dances. Correlations between viral abundances and suspended solids suggest that viruses sorbed to suspended material in the water column may settle ou t and contribute to the benthic viral population. Virus production was meas ured by a time course increase of viral abundance in seawater using a dilut ion technique. Virus production was highest in eutrophic waters of the Bris bane River, and addition of inorganic nutrients (NO3- + NH + PO43- + SiO3) stimulated viral production rates at all stations by 14-52% above ambient, suggesting that inorganic nutrient availability may play a key role in aqua tic viral abundance.