photic zone

The surface waters of seas, oceans, and lakes penetrated by light and inhabited by plankton. In clear water light at the red end of the spectrum is absorbed and only blue light penetrates to lower levels. However in turbid water blue light is preferentially absorbed. The depth at which the rate of production of carbohydrates by photosynthesis is equalled by the rate of utilization by respiration is termed the compensation level. Most of the plankton is found in the top 10 m.