MEPS 279:3-12 (2004)  -  doi:10.3354/meps279003

Bacterial and viral abundance in Ross Sea summer pack ice communities

Marcia M. Gowing1,6,*, David L. Garrison1,3, Angela H. Gibson1, Jonathan M. Krupp2, Martin O. Jeffries4, Christian H. Fritsen5

1Institute of Marine Sciences, and
2Microscopy and Imaging Laboratory, University of California, Santa Cruz, California 95064, USA
3Division of Ocean Sciences, National Science Foundation, 4201 Wilson Boulevard, Arlington, Virginia 22230, USA
4Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA
5Desert Research Institute, Division of Earth and Ecosystem Sciences, Reno, Nevada 89512, USA
6Present address: 11513 Stone Avenue North, Apartment D-227, Seattle, Washington 98133, USA

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 × 105 to 6.7 × 106 ml-1 melted sample and viral abundance from 6.3 × 106 to 1.19 × 108 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.

KEY WORDS: Bacteria · Viruses · Pack ice · Algal blooms · Ross Sea

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