The photosynthetic activity of endolithic communities at three sites in the Ross Sea Region, including Mt Falconer in the Taylor Valley, Linnaeus Terrace in the Asgard Range, the Nussbaumriegel in the Taylor Valley, Battleship Promontory and Granite Harbour was studied in situ. Microsensors were installed at all field locations in boreholes in sample rocks to measure oxygen concentration, pH and ... chlorophyll fluorescence at various depths. Microclimate sensors were installed and measured ambient air temperature and relative air humidity 30 cm above the rock surface, rock surface temperature, stone temperature, (5cm deep), soil temperature (20cm deep) temperature of the chasmoendolithic habitat at two different points and ambient light intensity (PAR). Rocks with endolithic organisms were sampled and analysed for biodiversity and compared among the different sites. Dry samples were analysed for community structure by microscopical examination (TEM, SEM, fluorescence microscopy and confocal microscopy with and without staining) and compared to the source location to interpret the effects of altitude and rock type. Field experiments were conducted to measure how long photosystem II was active in the chasmoendolithic habitat by measuring photosynthetic yield over 24 hours and generating a light response curve and the photosynthetic activity after the endolithic algae had been uncovered by chiselling. Samples were also analysed for total biomass, chlorophyll a content, 14C age, stable isotopes (nitrogen and carbon), morphological and genetic diversity studies, test for alkalisation, CO2 gas exchange capacity, photosynthetic capacity, radiocarbon dating of age, isolation and cultivation of characteristic species.