DIEL PATTERNS IN LIGHT ABSORPTION AND ABSORPTION EFFICIENCY FACTORS OF<i>ISOCHRYSIS GALBANA</i>(PRYMNESIOPHYCEAE)¹

Abstract

The chl a specific absorption coefficients [ a * (λ), m 2 ·mg chl a − 1 ] were examined in chemostat culture of the Prymnesiophyceae Isochrysis galbana (Parke) under a 12:12‐h light:dark cycle at low light (75 μmol photons·m − 2 ·s − 1 ) and high light (500 μmol photons· m − 2 ·s − 1 ) conditions. Other associated measurements such as pigment composition, cell density, and diameter as the measure of cell size were also made at the two light regimes every 2 h for 2 days to confirm the periodicity. A distinct diel variability was observed for the a * (λ) with maxima near dawn and minima near dusk. The magnitude of diel variation in a * (440) was 15% at low light and 22% at high light. Pronounced diel patterns were observed for cell size with minima near dawn and maxima near dusk. The magnitude of diel variation in cell size was 9.3% at low light and 21% at high light. The absorption efficiency factors [ Q a (440)] were determined by reconstruction using intracellular concentrations of pigments and cell size. The Q a (440) also showed a distinct diel variability, with minima near dawn and maxima near dusk. The diel variation in a * (λ) and Q a (λ) was primarily caused by changes in cell size due to growth, although there was some influence from diel variations in the intracellular pigment concentrations. The results presented here indicated that diel variation in a * (λ) was an important component of the optical characterization of phytoplankton.