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Articles

Photoadaptation in Marine Phytoplankton ¹

Changes in Spectral Absorption and Excitation of Chlorophyll a Fluorescence

Food Chain Research Group, Scripps Institution of Oceanography, University of California, La Jolla, California 92093, Department of Biological Sciences, University of Southern California, University Park, Los Angeles, California 90089-0371

The optical properties of marine phytoplankton were examined by measuring the absorption spectra and fluorescence excitation spectra of chlorophyll a for natural marine particles collected on glass fiber filters. Samples were collected at different depths from stations in temperate waters of the Southern California Bight and in polar waters of the Scotia and Ross Seas. At all stations, phytoplankton fluorescence excitation and absorption spectra changed systematically with depth and vertical stability of the water columns. In samples from deeper waters, both absorption and chlorophyll a fluorescence excitation spectra showed enhancement in the blue-to-green portion of the spectrum (470-560 nm) relative to that at 440 nm. Since similar changes in absorption and excitation were induced by incubating sea water samples at different light intensities, the changes in optical properties can be attributed to photoadaptation of the phytoplankton. The data indicate that in the natural populations studied, shade adaptation caused increases in the concentration of photosynthetic accessory pigments relative to chlorophyll a. These changes in cellular pigment composition were detectable within less than 1 day. Comparisons of absorption spectra with fluorescence excitation spectra indicate an apparent increase in the efficiency of sensitization of chlorophyll a fluorescence in the blue and green spectral regions for low light populations.

¹ Supported in part by grants to D. A. K. from the National Environmental Satellite Service (04-7-158-44123) and the National Aeronautics and Space Administration (NAGW-317), by a grant to O. H. H. from the National Science Foundation (DPP79-21295) and by United States Department of Energy Contract DE-AM03-76SF00010. A. N. was supported by the G. Meyerbaum Fund for Oceanography and by the Solar Energy Institute, Contract No. XK-0-9111-1 (W. H. Thomas, P. I.).