Scientists at the Marine Biological Laboratory (MBL) have found "bipolar" species of bacteria that occur in the Arctic and Antarctic, but nowhere else. The discovery is reported this week in Proceedings of the National Academy of Sciences. Their study shows that marine bacteria are not just homogenous populations in the ocean, but they are more selective than that. Different bacteria prefer certain temperatures, levels of nutrients, light and salinity. Understanding their distribution is really important because bacteria play crucial roles in the ocean ecosystem services we rely upon, such as providing food stocks, and in climate. As our environment changes and global temperatures become warmer, we have to pay attention to shifts in bacterial distributions, as well as flora and fauna.

Bacteria and other microbes are essential catalysts for all of the chemical reactions that shape planetary change and habitability, such as cycling of carbon, nitrogen, oxygen, sulfur, iron, and manganese through the environment. Marine microbes regulate the composition of the atmosphere, influence climate, recycle nutrients, and decompose pollutants. Without microbes, multicellular animals on Earth would not have evolved or persisted over the past 500 million years.

The study is one of many born from the gigantic database on marine microbes created during the International Census of Marine Microbes (ICoMM), a part of the Census of Marine Life. It also contains data from MIRADA‐LTERS (Microbial Inventory Research Across Diverse Aquatic Long‐Term Ecological Research Sites). Over a six‐year period (2004 to 2010), ICoMM scientists from many nations collected water samples and, crucially, related environmental data from a broad range of marine ecosystems, from open ocean to undersea volcanoes, densely populated coastlines to Polar seas. MIRADA‐ LTERS also contributed to the census.

Rather than buttressing what is known as the Baas‐Becking tenet in microbial ecology ("Everything is everywhere, but the environment selects") the present study suggests dispersal limitation plays an important role in marine bacterial distributions before environmental selection makes a difference. The ocean currents that occur on the equator may be physical and in some cases geochemical barriers that limit the distribution of certain types of bacteria. This means a warming climate, which affects ocean temperature, salinity, pH levels, and circulation patterns, can significantly impact marine microbial distributions.

Journal Reference: Sul WJ, Oliver TA, Ducklow HW, Amaral‐Zettler LA, and Sogin ML. Marine bacteria exhibit a bipolar distribution. PNAS, January 14, 2013 DOI: 10.1073/pnas.1212424110.