Explain how light and depth determine the distribution of organisms in marine ecosystems.

The marine animals rely on the primary productions for energy sources. So, we can map the global distributions of marine life based on the distribution of chlorophyll (through sunlight) and primary produces like food for animals.

The animals are divided in terms of temperature, salinity and light availability in the ocean. Hence the ocean has 3 parts- Euphotic zone, Twilight zone and deep sea zone.

Life in the euphotic zone is very diverse due to presence of sunlight where it permeates the water column making photosynthesis possible. Some examples of animals living here are- jellyfish, sharks, sea turtles etc.

The twilight zone is 1000 - 4000 meters below the surface of the ocean. Since there is no sunlight, a lot of animals in this zone don't have eyes. Examples- algae, coelacanths, copepods, crabs and other crustaceans.

The deep sea zone is the zone where water pressure is so high that the marine life that live here need to be able to withstand the pressure. For example-  flashlight fish, cookiecutter shark, bristlemouths etc.

the cell cycle is the final answer! : )