Temporal variations in viral distributions in the anoxic Cariaco Basin

Virus-like particles (VLP), collected from the permanently anoxic Cariaco Basin between 10 October 1996 and 2 November 1999, were enumerated in water column and sediment trap samples. Vertical distributions of VLP from 18 depths between 7 and 1310 m generally corresponded to those of bacterial abundance and bacterial net production (BNP), with primary maxima consistently found in surface waters and midwater maxima near the O-2/H2S interface. Temporal variations in VLP concentrations (0.81 to 630 x 10(8) VLP l(-1)) were highly correlated with chlorophyll a (chl a), bacterial abundance and BNP in the upper 250 m. In the redox transition zone (RTZ = 250 to 450 m), VLP abundance covaried with bacterial growth rates, but not bacterial abundance nor chemoautotrophic production. In the anoxic layer (>450 m), temporal variations in VLP abundance were not significantly correlated with any measured variable. In the RTZ, the median VLP:bacteria ratio (VBR = 3) was significantly lower than in the oxic (VBR = 16) and anoxic (VBR = 31) layers for all observations, suggesting varying relationships between viruses, hosts and environment among these layers. Vertical fluxes of VLP associated with sedimenting debris varied between 0.39 and 520 x 10(9) VLP m(-2) d(-1), a range similar to bacteria (0.88 to 330 x 10(9) bacteria m(-2) d(-1)). VBRs in the sinking inventories were very low, varying from 0.01 to 1.2 and averaging 0.60, suggesting that VLP are not as numerically important in sinking particles as they are in suspended communities. Comparisons of sinking fluxes with suspended VLP inventories indicate that vertical transport is relatively unimportant in redistributing viruses in the water column. Estimated removal rates by sinking from the oxic, transition and anoxic layers averaged 0.11% mo(-1) (n = 16) for apparent VLP.