In the maritime Antarctic the cyanobacterial lichen puberulum prefers habitats that are water-supplied by snowmelt at least for a part of the year. In springtime thalli of L. puberulum can be found fully hydrated for extended periods of time even during clear days with strong irradiance. Although the combination of low thallus temperatures and strong sun radiation is generally known to be injurious to the photosy stem II none of the established indicators of photoinhibition were observed. During and subsequent to a 3 h treatment with 1600 pmol m'2 s'1 PPFD CO:-gas exchange and Chl-a- fluorescence remained stable on the same level. This elucidates that L. puberulum is well adapted to tolerate extreme irradiance conditions likely to impact lichens growing in meltwater flurries without any need for damage-repair-cycles