Light Zones in Aquatic Habitats There is a light zonation in deep lakes and oceans

$(i)$ Littoral Zone It is shallow coastal region. Light is able to pass through shallow water and reach the bottom. Therefore, producers occur throughout from surface to bottom

$(ii)$ Limnetic Zone It is open water zone where water is very deep. Amount of oxygen and light decreases with depth.

Limnetic zone has following three parts

Photic Zone It is upper part of limetic zone to which light can penetrate. Depth is up to $200 \,m$. The upper part of photic zone, called euphotic zone, receives light more than the compensation point. Its depth is $20-80 \,m$. The lower part of the photic zone, called disphotic zone (twilight zone), receives light at or below the compensation point.

Blue light being made of short wave radiations can reach the deepest. Red light has poor penetrability. In sea the green algae remain near the surface, brown algae in intermediate depths, while red algae flourish the deepest in the photic zone

Aphotic$/$Profundal Zone It is zone of deep water below the photic zone and above the bottom to which light does not penetrate. The zone is, therefore, in perpetual darkness. Producer to not occur in this part. Instead only consumers are found

Benthic Zone It is the bottom zone. In deep lakes and seas, the bottom is also in perpetual darkness but in shallow waters, light does penetrate