The effect of water motion on short-term rates of photosynthesis by marine phytoplankton.

Phytoplankton respond to variations in light intensity as they are mixed through the water column. Changes in pigment content are characteristic of the relatively slow response of 'sun-shade' photoacclimation that occurs on timescales typical of mixing in the open ocean. In estuaries, the variations are much faster and induce correspondingly rapid changes in the activity (rather than abundance) of different components of the photosynthetic apparatus. These components modulate light harvesting and Calvin cycle activity, or protect the pigment bed from excess energy absorption. When the protective capacity is exceeded, photoinhibition occurs. All these mechanisms modulate the rate of photosynthesis in situ.