How does the photic zone differ from the aphotic zone?

In an oceanic environment, the photic zone is the zone where light can be received, it's usually from 0 to 200 m deep, but this depth can be modified by the turbidity of the water.

The aphotic zone is the zone where no light is received, it goes from 200 to the bottom of the sea.

The difference is about the primary production and the oxygen concentration and so the pH of the water.

In the photic zone, there is light, so vegetal organism (micro and macro algae) can grow and realize the , and so produce compounds and Oxygen from the CO2 in the water.

In the aphotic zone, there is no light, so vegetal organism can't grow and realize the photosynthesis, the CO2 is accumulated, there is less Oxygen and the pH is lower than in the photic zone.

All the living organism develop adaptation to the lack of light like bigger eyes for the abyssal fish and cephalopods, light emission for the abyssal fish and shrimps to mate, defend, or attack and the tapetum lucidum, which is a structure in the eyes that reflect the incoming light, the cat got one.

Hope this helps you, have a good day!