LIGHT-ABSORPTION BY SEAGRASS POSIDONIA-OCEANICA LEAVES

We examined the importance of pigment content and packaging within plant tissues for light absorption by Posidonia oceanica leaves from different locations along the Spanish Mediterranean coast. Pigments of P. oceanica leaves absorbed 70.5 to 97.1 % of incident light (at 675 nm); the light absorbed by pigments increased with increasing chlorophyll density. The efficiency of chlorophyll a in absorbing light (i.e. the chlorophyll a-specific light absorption) also decreased significantly (p < 0.001) with increasing pigment packaging (i.e. concentration) within the leaves, although the light absorbed per unit biomass increased with increasing pigment concentration. The positive trend between light absorption and chlorophyll density found for P. oceanica leaves was also found to apply to 12 other seagrass species from the Atlantic, Pacific, Caribbean, South China and Mediterranean Seas. The similarity between the patterns in light absorption by seagrass leaves described here and those previously described for phytoplankton suggests that these patterns reflect constraints on light absorption by phototrophic organisms which may apply to most aquatic plants.