Aquatic ecology and Biodiversity

Unit 5- Productivity

5.2.3. Light
Photosynthesis is directly proportional to the light intensity of solar radiation. About 80% incident visible light reaches 120m. depth in a clear offshore waters and 10-20 m. in turbid inshore waters. Of the incident light that falls on the surface of the sea only 0.02 to 2% of light will be used by most plants. Light inhabitation occurred at light greater than saturation levels. In bright light (12hrs.) plants receive more illumination than saturation level at the surface of water. During day hours, max photosynthesis occurs below the surface between 5-20 meters. The high phytoplankton biomass found in the euphonic zone by shade plankton. Light does not limit photosynthetic production in tropical water, while in temperate regions where spring production is due to increase of solar radiation. Light saturation point of different plankton by Ryther ( 1956)