Bacterial and viral abundance in Ross Sea summer pack ice communities

Abstract

Abundance of single, non-attached bacteria and viruses <110 nm (likely to have infected bacteria) were determined for surface, interior and bottom ice microhabitats between 66 and 75°S in the Ross Sea during the austral summer of 1999. Emphasis was on sites of ice algal blooms, and bacterial abundance was examined with respect to physical characteristics, chlorophyll a, phaeophytin and, in particular, microbial communities. Bacterial abundance ranged from 1.5 × 10 5 to 6.7 × 10 6 ml -1 melted sample and viral abundance from 6.3 × 10 6 to 1.19 × 10 8 ml -1 melted sample over all the microhabitats. Neither bacterial nor viral abundance differed among microhabitats, and bacterial abundance was not related to physical characteristics of the habitats. Although bacterial abundance was positively correlated with chlorophyll a and phaeophytin concentrations, only chlorophyll a was significant in explaining a small (28%) degree of the variability in bacterial abundance. Abundance of diatoms, heterotrophic dinoflagellates and other flagellates, however, explained 85% of the variability in bacterial abundance; these groups were positively correlated with bacterial abundance. Neither viral lysis nor grazing by bacteriovores appeared to be strong controls of bacterial abundance. Community analysis showed that samples were > 90% similar with respect to abundance of bacteria, viruses, and microeukaryote groups. Distinct clusters could be attributed to different algal bloom stages, with relationships to Phaeocystis spp. blooms being particularly apparent, indicating the strength of algal blooms as processes structuring microbial communities. Microbial communities in Ross Sea summer ice microhabitats could furthermore be viewed within the same general successional sequence characteristic of algal blooms in polar and temperate marine waters.

Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition

“…Bacterial abundances in the sea ice on the Mackenzie Shelf were within the range previously observed for Antarctic (Gowing et al 2004 and references therein) and Arctic sea ice (Bunch & Harland 1990, Gradinger & Zhang 1997. Bacterial abundances from the ice-water interface were also comparable with previous estimates for surface waters in the same area (Garneau et al 2006).…”

Exopolymer particles: microbial hotspots of enhanced bacterial activity in Arctic fast ice (Chukchi Sea)

“…High virus concentrations affecting both eukaryote and prokaryote populations have been reported from the sea-ice habitat (Maranger et al 1994, Borriss et al 2003, Gowing 2003, Gowing et al 2004 and are suggested to significantly affect sea-ice bacterial populations in winter and early spring (Wells & Deming 2006). …”

Sea-ice microbial communities in the Ross Sea: autumn and summer biota

“…such as chl a measurements). Our studies of ice communities in the Ross Sea have included the consideration of a range of microbial forms from viruses (Gowing et al 2002, Gowing 2003 and bacteria (Stewart et al 2001, Gowing et al 2004) to protists. Here, we describe the community composition of the ice biota in pack ice regions of the Ross Sea during the autumn to winter transition and during the summer.…”