Abstract
Primary production models and pigment algorithms for remote optical systems including satellites, moorings, or drifters depend on an improved understanding of the relationship between spectral light absorption, pigments, and photosynthesis for species of phytoplankton that are widespread and numerically abundant. Cultures of colonial Phaeocystis antarctica , a prymnesiophyte that can dominate the phytoplankton community in the Southern Ocean, were grown under blue light at seven different levels ranging from 14 to 542 µmol quanta m −2 s −1 at 4°C under nutrient‐replete conditions. Chlorophyll‐specific absorption (a * ph ) at 436 nm increased linearly from 0.03 to 0.11 m 2 mg chlorophyll a −1 with increasing light intensities. This variability is attributed to pigment packaging effects and pigmentation. The 2.5‐fold range in the values of a * ph (676 nm) demonstrates significant pigment packaging effects due to the intracellular pigment content, single cell diameter within the colony, and thylakoid stacking. Quantum yield for growth (Φ μ ) varied 30‐fold, ranging from 0.003 to 0.09 mol carbon fixed (mol quanta absorbed) −1 . Under low light conditions, the relatively high (Φ μ ) and high a * ph (λ) may enable Phaeocystis to accumulate a seed population to initiate blooms at the beginning of spring when light levels are low, mixed layers are deep, and sea ice is still significant. These aspects of its photophysiology may contribute to the ecological success of Phaeocystis in polar regions.