Vertical Distribution of Photosynthetic Pigments and the Penetration of Light in Marine Sediments

Methods for studying the vertical distribution of some photosynthetic pigments in marine sediments (chlorophyll a, bacteriochlorophyll a, phycocyanin and a watersoluble cryptomonad pigment) are described and examples of their vertical distribution and of absolute counts of microalgae from various types of shallow water sediments are given. In all types of sediments many pigmented cells are found below the photic zone. Light penetration in different kinds of sediment was measured for white and colored light. In pigment-free sand long waved light penetrates furthest; this is of significance for the photosynthetic bacteria which live deeper in the sediment than algae and utilize near-infrared light for photosynthesis. The photic zone of very fine sand is of half the thickness of that found in coarse sand. The percentage of light absorbed by the photosynthetic pigments was estimated to be less than 10-20% of the total incident light in rich localities, a low value compared to other plant communities. The amount of chlorophyll a per unit area of the photic zone of different sediments was estimated and found to be lower than estimates from other plant communities.