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 Cor nwallis Island in the Canadian High Arctic: (1) sheets or spherical colonie s of Nostoc (up to 20 mm diameter): (2) biofilms up to 7 mm thick, dominate d almost exclusively by Oscillatoria; (3) microbial mars up to 8 mm thick c ontaining several taxa, particularly Scytonema and Phormidium. The abundanc e of heterocystous genera (communities 1 and 3) implies that N-2 fixation p lays 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. Spectroradio metric 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 photo synthetically active radiation band (400-700 nm), restricted to the wavelen gths of the yellow-red waveband (550-650 nm). The surface screening of high energy wavelengths may confer an adaptive advantage to these communities w hich grow under continuous light during the polar summer. (C) 1999 Federati on of European Microbiological Societies. Published by Elsevier Science B.V . All rights reserved.