An Oceanographic Perspective on Microbial Life at Low Temperatures

At the typical subzero temperatures of polar oceans, neither the growth nor survival strategies of heterotrophic microorganisms, in particular bacteria, are well understood. Protistan and viral predation on bacteria in high-latitude seas is a subject of current interest, but the potential inhibition of bacterial acquisition of food by very low temperatures remains the most debated issue in polar marine microbiology. If significant limitations are imposed on bacterial heterotrophy in seawater by nearfreezing temperatures, then the flow of organic matter through the microbial loop and associated respiratory loss of carbon from the system (Yager, 1996) will also be limited. If the temperature limitations are differential (if phytoplankton growth can outcompete bacterial growth at subzero temperatures), as documented by Pomeroy and Deibel (1986), then the highly efficient food webs, often weighted towards higher trophic levels, that characterize polar marine ecosystems (Petersen and Curtis, 1980) are mechanistically explained.