It’s the small things that count

This article was part of the original Looking South magazine

Microscopic viruses are the most abundant biological agents in antarctic waters occurring in concentrations of over 100 million per millilitre (ml) of water. They have a very important, if little-understood, role in the biological processes of the Southern Ocean.

In temperate marine microbial food webs, viruses are believed to cause about 50 percent of the mortality of bacteria, inhibiting oceanic productivity by up to 78 percent. They are also believed to affect nutrient flow and microbial community structure. Viruses therefore influence the food available to grazing animals and those marine processes which affect climate.

Although viruses have been found in Antarctic waters, little is known about their distribution and abundance in the Southern Ocean or their role in antarctic marine ecosystems. Biologists from the Australian Antarctic Division and James Cook University have been investigating their abundance, and their association with microorganisms in surface waters between Tasmania and Antarctica and in the sea-ice zone. The concentration of viruses varies substantially with latitude across the Southern Ocean and also differs between winter and spring. Their abundance ranges between about half a million per ml in winter to over four million per ml near Tasmania and in the pack ice zone in spring.

Other researchers have found that viral abundance is related to bacterial concentration in temperate waters with about ten virus particles for every bacterium. However, in springtime in the Southern Ocean the relationship between the number of viruses and bacteria is highly variable and dramatically different in the sea-ice zone.

Early investigations suggest that while the role of viruses in the Southern Ocean is likely to be similar to that in other parts of the global ocean, interactions between viruses and bacteria in the sea-ice zone may differ from those in the open ocean. Knowing how they function in Southern Ocean ecosystems will help us understand the biological processes that control the food availability for krill and other grazers as well as the ways in which Southern Ocean living systems affect world climate.

For more information, email: bio@aad.gov.au

See more information on the Australian Antarctic Research Biology program