Spatial distributions of bacterio- and virioplankton in the Chukchi Sea during summer 2012

Abstract

Bacteria and viruses are at the bottom of the marine food web and play important roles in

biogeochemical cycles of organic matters and nutrients. In the Chukchi Sea, there are 4 distinct

water masses during summer; surface mixed layer water, Pacific summer water, Pacific winter water

and Atlantic water. These water masses can be distinguished by its unique hydrographical

properties, hypothesizing that spatial distributions of bacteria and viruses may be reflected by

these different ecological regimes. To test this hypothesis, we investigated 35 depth-profiles of

bacterial (BA) and viral abundances (VA) in an area covering ca. 900x400 km2 in the Chukchi Sea

(73-82oN, 173oE-153oW) during the icebreaker R/V Araon expedition (Aug 1 to Sep 10 in 2012). To

avoid loss of microbes due to long-term storage, bacteria and viruses were counted within a day of

sampling on aboard using an epifluorescence microscope isolated from the vibrations of the

research vessel. BA ranged from 0.1×105 cells ml-1 to 16.4×105 cells ml-1 in the study area. In

most stations, BA showed the maximum value at the surface or at the subsurface chlorophyll maximum

depth, and tended to decrease with depth in water column. VA was on average 19-fold higher than

BA, but depth profiles of VA showed similar patterns to those of BA. Our results showed that there

was spatial heterogeneity in bacterial and viral abundances among staater, Pacific summer water, Pacific winter water

and Atlantic water. These water masses can be distinguished by its unique hydrographical

properties, hypothesizing that spatial distributions of bacteria and viruses may be reflected by

these different ecological regimes. To test this hypothesis, we investigated 35 depth-profiles of

bacterial (BA) and viral abundances (VA) in an area covering ca. 900x400 km2 in the Chukchi Sea

(73-82oN, 173oE-153oW) during the icebreaker R/V Araon expedition (Aug 1 to Sep 10 in 2012). To

avoid loss of microbes