below sea level can be broken up into different "life zones" as follows:
The neritic zone is a region of open water directly above the continental shelf, and is the most productive area in the ocean. It is on the epipelagic level.
The oceanic zone is the water that spreads out from beyond the continental shelf.
The epipelagic zone is one of the highest and most photic (well-lit) zones. Sunlight allows organisms to thrive such as zooplankton or phytoplankton. This, in turn, attracts many fish and other marine life that would feed on plankton.
The mesopelagic zone is a euphotic (semi-lit) one where the collection of organisms mentioned above feed on plankton. The usual depth for ambient light to start fading from the water is about 1000 meters below the surface. The first visible color to fade is the red spectrum.
The bathypelagic level is another euphotic zone that starts at about 4000 meters under sea level. The water starts to become colder, and the last colors to fade are green and blue. Photosynthesizing plankton begins to absent itself as darkness sets in, and modified creatures that don't solely eat plankton or need light habit this zone.
The abyssopelagic zone is typically 9000 meters underwater and is completely aphotic (devoid of light). Sea life that requires no light lives down here, and can usually make its own light through a process known as bioluminescence. Autotrophic organisms that dwell around deep-sea vents are found instead of photosynthetic ones.
The benthic zone is composed of the ocean floor and upper sediment, and also completely aphotic.