Light absorption and size scaling of light‐limited metabolism in marine diatoms

Previous studies have found that the size‐scaling exponent of metabolic rates in unicellular algae often deviates from the exponent of −1/4 usually found for heterotrophs. This study confirms a significant linear relationship between log cell volume (mm 3 ) and log intrinsic growth rate (h −1 ), carbon‐normalized photosynthetic capacity and performance (h −1 ), and carbon−normalized respiratory rate (h −1 ) for eight marine centric diatoms under nutrient−saturated, light‐limited conditions. The intrinsic growth rate and carbon‐normalized respiratory rate have size‐scaling exponents not significantly different from −1/4, whereas the carbon‐specific photosynthetic rates deviate from −1/4. The size dependence of the optical absorption cross section (m 2 mg chlorophyll a −1 ) due to the package effect provides a mechanistic model that explains the anomalous size scaling of the anabolic rates of unicellular phytoplankton.