The effect of water motion on short-term rates of photosynthesis by marinephytoplankton

Phytoplankton respond to variations in light intensity as they are mixed th rough the water column. Changes in pigment content are characteristic of th e relatively slow response of 'sun-shade' photoacclimation that occurs on t imescales 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 appara tus. These components modulate light harvesting and Calvin cycle activity, or protect the pigment bed from excess energy absorption. When the protecti ve capacity is exceeded, photoinhibition occurs. All these mechanisms modul ate the rate of photosynthesis in situ.