The shapes of excitation spectra for chlorophyll a fluorescence in the far-red (730 nm) were compared under physiological conditions to those for chlorophyll a fluorescence in the red (685 nm) and to action spectra for photosynthetic oxygen production in diversely pigmented algae. Species examined as representatives of the prominent oceanic light harvesting systems were Chaetoceros graciljs, Glenodinium sp., Ulva sp., Porphyrid~um cruentum and Chroomonas sp. Qualitatively, for any one alga, all 3 action spectra exhbited broadly similar spectral features, suggesting initial light harvesting for photosynthesis by the same major pigments, i.e. those commonly associated with photosystem 11. As such, measurement of fluorescence (in preference to may provide a useful and facile alternative to oxygen action spectra in assessing the full photosynthetic spectral performance (320 to 700 nm) of individua! phy!opl=nkta~ species er =ssernb!-.ges.