Variability in chlorophyll α specific absorption coefficient in marine phytoplankton as a function of cell size and irradiance

Size-dependence of chlorophyll a (Chl a) specific absorption coefficient a*(lambda) for six irradiances ranging from 25 to 750 mumol m(-2) s(-1) was quantified for six species of phytoplankton Of varying size. These included Bacillariophyceae Thalassiosira weissflogii, Chaetoceros gracilis and Coscinodiscus sp., Chlorophyceae Dunaliella tertiolecta, and Prymnesiophyceae Isochrysis galbana and Pleurochrysis carterae. For the six irradiances, statistically significant relationships were obtained between cell volume and a*(675), which decreased significantly with increasing cell volume at all irradiances. However, a*(440) showed a statistically significant relationship between cell volume and a* at only 25, 40 and 90 mumol m(-2) s(-1). The relative contributions of several pigments were estimated using the pigment-based reconstruction technique. At high irradiance, absorption by photoprotective pigments increased in relative importance. Under high light conditions, size-dependence of absorption at 440 nm weakens due to the effects of absorption by photoprotective pigments in the blue region of the spectrum. Thus observed variability in a* is dependent on the physiological characteristics of marine phytoplankton, the result of this study indicates that size-dependence of absorption is a robust characteristic of phytoplankton under low light conditions.