Community and pigment structure of Arctic cyanobacterial assemblages: the occurrence and distribution of UV-absorbing compounds

Three groups uf cyanobacterial communities were widely distributed ill the benthic environment of lakes, ponds and streams on Ellesmere Island and Cornwallis Island in the Canadian High Arctic: (1) sheets or spherical colonies of Nostoc (up to 20 mm diameter): (2) biofilms up to 7 mm thick, dominated almost exclusively by Oscillatoria; (3) microbial mars up to 8 mm thick containing several taxa, particularly Scytonema and Phormidium. The abundance of heterocystous genera (communities 1 and 3) implies that N-2 fixation plays an important role in the nitrogen economy of these ecosystems. Most of the communities were rich in pigments absorbing in the UV-blue end of the spectrum, such as scytonemin and mycosporine-like amino acids. Spectroradiometric analyses of sections of the communities showed that short wavelength radiation did not reach the bottom layer where phycobiliprotein-rich cells were located. This lower community experienced low irradiance in the photosynthetically active radiation band (400-700 nm), restricted to the wavelengths of the yellow-red waveband (550-650 nm). The surface screening of high energy wavelengths may confer an adaptive advantage to these communities which grow under continuous light during the polar summer. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.