Light- Almost all forms of life in aquatic habitats are either directly or indirectly influenced by light, because primary production is mainly through photosynthesis. Since algae and photosynthetic bacteria are involved in photosynthesis, they are the most important forms with respect to light. Light is also important in the spatial distribution of microorganisms, especially the photosynthetic forms.
Photosynthetic micro-organisms are mainly restricted to the upper layers of aquatic systems, the photic zone, where effective penetration of light occurs. Although photosynthesis is confined to the upper 50 to 125m of the water bodies, the depth of the photic zone may vary depending upon the latitude, season and turbidity. Apart from the decrease in the quantity of light with depth there is also a change in the color of the light. Blue light is transmitted most while the red is the least.
