In situ response of phytoplankton fluorescence to rapid variations in light1

Phytoplankton chlorophyll a fluorescence responded to rapid fluctuations in light intensity in Lake Tahoe at three depths: 10, 35, and 60 m. Fluorescence yield was negatively correlated with surface irradiance at all depths, but there was a strong depth dependence in the intensity of this response. Phytoplankton at 35 m reacted more strongly to fluctuations than those at 10 or 60 in and therefore could show a noticeable response to more rapid variations. This may have been due to near‐optimal light levels at 35 m, light inhibition at 10 m, and light limitation at 60 m.