Photoacclimation of four marine phytoplankton species to irradiance and nutrient availability

Photoacclimation to different light and nutrient regimes was studied in 4 common marine phytoplankton species from northern European coastal waters. Significant changes were observed for all species in their cellular nutrient content, pigment packaging and composition, and chl a-specific in vivo light absorption (a*_chla(¿)). From exponential to stationary growth, the C:N and carotenoid:chl a ratios increased, while the cellular chl a content decreased. All phytoplankton species acclimated to increasing irradiance by reducing their cellular chl a content and increasing the carotenoid:chl a ratio, resulting in higher chl a-specific absorption coefficients (a*_chla). Similar results were observed for N-depleted cultures. Although acclimation to different irradiance and nutrient conditions introduced a substantial variability in pigment composition and intracellular pigment concentration, significant interspecies differences in a*_chla were still apparent. The interspecies differences were primarily due to differences in cell size, which covaried with pigment packaging and composition. On this basis, we suggest that optical acclimation (i.e. changes in pigment composition and packaging) to the prevailing growth conditions (light, temperature and nutrient availability) is less important than differences in phytoplankton composition (dominant cell size and pigment composition) for the variation in a*_chla(¿) of natural phytoplankton communities.