Search for a command to run...
Although cyanobacteria are often thought of as warm water organisms. they are the predominant biota in cold polar environments such as ice shelves. glaciers. glacial meltwater streams and ice-capped lakes. Cyanobacteria are the primary colonizers of glacial moraines after the retreat of ice sheets. and they play an important role in the carbon and nitrogen economy of tundra and polar desert soils. Various communities dominated by cyanobacteria inhabit exposed rock surfaces. while others occur within fissures and the interstitial spaces between crystals in certain Arctic and Antarctic rock types (See Chapter 13). Highly pigmented microbial mats dominated by Nostoc or oscillatorians (Oscillatoriaceae) are a feature of streams. lakes and ponds in both polar regions. with extreme accumulations up to 90 cm thick and >40 μg Chla cm-2 at some sites. Picocyanobacteria often dominate the phytoplankton of polar and subpolar lakes. In the coastal saline lakes of Antarctica picocyanobacteria achieve some of the highest natural concentrations on record. up to 8 x 106 cells mL-1. However. picocyanobacteria are conspicuously absent or rare in the adjacent polar oceans. The ecophysiological characteristics of high-latitude cyanobacteria that contribute to their success and dominance include: an ability to grow over a wide temperature range (but at slow rates); tolerance of desiccation, freezing and salinity stress; a variety of adaptive strategies against high levels of solar radiation (including ultraviolet radiation) in exposed habitats; and acclimation to shade allowing net growth in protected dim light environments. In many polar habitats, the large standing stocks of cyanobacterial biomass are the result of gradual accumulation over many seasons, with only minor losses via biotic and abiotic removal processes. Cyanobacteria are not successful in the polar oceans where slow, temperature-depressed and light-limited growth rates are unable to keep pace with the continuous losses due to grazing, advection and mixing.