Evaluating Underwater Light Availability for Phytoplankton: Mean Light Intensity in the Mixed Layer versus Attenuation Coefficient

The use of several light-related variables, such as the Secchi disc depth, euphotic and in particular, diffuse attenuation coefficient (Kd), is deeply rooted phytoplankton research, but these are not most appropriate indicators amount light available for photosynthesis. We argue that variable interest mean intensity mixed layer (Im), which represents to cells exposed throughout their life cycle, while being continuously layer. empirical data collected different coastal ecosystems southern Portugal demonstrate why Im should be preferred metric instead Kd. show that, although relationship between Kd inversely proportional, it always strong or even significant. Different values can associated with same Kd, distinct have physiological effects phytoplankton. Therefore, does capture photosynthesis, given unlike Im, calculation consider depth we urge researchers measurement when evaluating processes ecology.