LIGHT-ABSORPTION AND QUANTUM YIELD FOR GROWTH IN 5 SPECIES OF MARINE MACROALGAE

Light utilization efficiency in five species of marine macroalgae was measured in laboratory growth experiments (13-41 days duration) at different irradiances at 7-degrees-C. All species acclimated to irradiance by changing their light absorption, resulting in a peak in light absorption between 2 and 15 mumol.m-2.s-1. Light absorption increased with thallus-specific chlorophyll and carbon content according to linear inverse relationships between chlorophyll content (chl.area-1) and log[transmission] and between log[carbon content, C.area-1] and log[transmission]. Quantum yields for light-limited growth and estimated gross photosynthesis were calculated based on incident and absorbed light. Quantum yield for photosynthesis based on light absorbed by pigments was high (mean = 114 mmol C.mol-1 photons) and similar among the species. Quantum yield for net growth based on incident light was also high but more variable, between 22 and 75 mmol C.mol-1 photons. Differences among species were mainly due to differences in light absorption. In conclusion, all species acclimated to low light by increasing light absorption to the maximum attainable, and growth efficiencies based on absorbed light were close to the maximum theoretically possible.