Cyanobacteria are an ancient group of photosynthetic microbes that capture sunlight for energy using blue or red coloured proteins (called phycobiliproteins) in addition to chlorophyll a. The exact timing of appearance of the first cyanobacteria-like microbes on Earth is still unclear because of controversy over interpretation of the Precambrian fossil record, however they appear to have achieved much of their present-day diversity by at least 2 billion years ago.
Cyanobacteria include some 2000 species in 150 genera, with a great variety of shapes and sizes. Ecologically there are three major groups in the aquatic environment:
Bloom-formers: These species form large colonies that can produce toxic water blooms. They tend to be found in warm, stable, nutrient-rich lakes and are largely absent from the polar regions.
Mat-formers: These species form mats and films over the surface of submerged rocks and sediment. Some of the most spectacular examples of such mats occur in lakes, ponds and shallow streams in the Arctic and Antarctica. They are typically 1-2 mm in thickness, but in some lakes can form mucilaginous mats up to several cm thick.
Picoplankton: These are the tiniest of cyanobacteria cells, less than one thousandth of a mm in diameter. However, they are also the most abundant. In fact, two of the genera, Synechococcus and Prochlorococcus, are so widely distributed in the ocean that they are probably the most abundant photosynthetic cell types in the whole Biosphere. Picocyanobacteria are typically in low abundance or absent from cold arctic seas, however they are very common in lakes, ponds and even large arctic rivers.
Micrograph of a colony of the nitrogen-fixing genus Nostoc, from the High Arctic.
A continuous mat of orange coloured cyanobacteria coating the base of a pool in the forest-tundra region of subarctic Québec.
Cyanobacterial mats growing in lakes and pools on the surface of the Ward Hunt Ice Shelf.
A thermokarst pond at Bylot Island showing the rich development of microbial mats.
Fluorescence micrograph of the filamentous cyanobacteria (order Oscillatoriales) that often dominate the benthic mats in Arctic lakes and streams.
