Effects of nutrient-limitation and irradiance on marine phytoplankton pigments

Effects of nutrient and light regimes on the pigment composition of 12 species of marine phytoplankton, representing eight algal classes, were examined in batch cultures. During exponential growth, significant differences in pigment ratios caused by light were found for several pigments in six species. Cellular contents of lutein increased with increasing irradiance in Pyramimonas disomata andBrachiomonas sp. indicating a photoprotective role of this pigment. Nutrient regimes had a significant effect only on fucoxanthin:Chl a in Ditylum brightwellii. During stationary growth phases, fewer pigment to Chl a ratios were significantly affected by irradiance, but significant effects from nutrient-limitation were found on the ratio of most marker pigments to Chl a. In four cryptophytes, the alloxanthin:Chl a ratio increased from 1.3-fold up to 9-fold from exponential growth phase to N-limited stationary phase, illustrating different stability of the marker pigment to Chl a ratio within the same phytoplankton group and even within the same genus. Pigment ratios obtained from exponential and stationary growth phases and from low and high light conditions were applied to pigment data from natural phytoplankton populations from two Danish fjords using the matrix factorization program CHEMTAX. Comparison of calculated phytoplankton compositions with direct phytoplankton counts showed the best agreement for exponential growth phase ratios from medium or low light intensities. Discrepancies between community structure described by microscopy and by using pigment analysis are discussed.