Downward irradiance spectra with depth in microbial mats Nb3 (a) and Nb4 (b) from Nakabusa hot spring. Arrows indicate major attenuation peaks from absorption of photosynthetic pigments (Chl a, 440 and 678 nm; phycoerythrin (PE), 588 nm; phycocyanin (PC), 615 nm; BChl c, 742 nm; BChl a, 802 and 880 nm).