• acclimation;
  • field investigation;
  • light dose;
  • light intensity;
  • Palmaria palmata;
  • photosynthesis;
  • pigmentation;
  • Rhodophyta;
  • zonation

The acclimation of the photosynthetic apparatus of Palmaria palmata (L.) to light intensity was examined in the field and under laboratory conditions. Algae from 3 different shore levels and from laboratory cultures adapted to 6 different photon flux densities were compared. This was done on the basis of light doses, which were delivered by different light regimes in the field and in the laboratory. Laboratory samples were adjusted to constant photon flux densities between 7 and 569 μmol photons·m2·s1 in a 16:8 light:dark photoperiod. Under field conditions the daily amplitudes reached up to approximately 2000 μmol photons·m2·s1 within a natural daily light course. Over the course of 14 days the light doses resulting from those different regimes are similar for both treatments. An increasing growth rate per day with increasing light doses was observed in the laboratory. Growth was saturated at 113 mol photons·m2·14 d1. Light saturation points (Ek) of photosynthesis increased with increasing light doses for both field and laboratory samples, and all Ek values were significantly related to the growth light dose. A correlation between fresh weight-related lutein content and growth light dose was found for laboratory samples only, whereas the lutein:chlorophyll a (chl a) ratio was strongly correlated with Ek for laboratory and field samples. The content of chl a and phycoerythrin (PE) per fresh weight decreased significantly with increasing light doses under field conditions. Simultaneously, the PE:chl a ratio increased, whereas this ratio was not influenced by laboratory treatments. The correspondence of Ek values for field and laboratory treatments indicated that they were affected mainly by light dose. However, the variability in pigmentation was mainly dependent on temporal variability in light intensity (the amplitude of variations in incident light).