The pelagic zone is subdivided into five vertical regions. From the top down, these are:
The epipelagic, or sunlight zone, is the ocean's topmost layer and the only one that receives enough sunlight for photosynthesis. It extends from the surface down to about 200 meters and is home to nearly 90% of all marine life. Because of the light and warmth, this zone supports the ocean's primary production and forms the base of the marine food web. It has the lowest water pressure and the highest oxygen levels, allowing a wide variety of species to thrive. Common organisms include plankton, jellyfish, seaweed, tuna, dolphins, whales, and sharks. This zone is also where the ocean interacts directly with the atmosphere, influencing climate and weather patterns.
Beneath the sunlight zone lies the mesopelagic, or twilight zone, where light begins to fade and temperatures drop sharply. Sunlight here is too weak for photosynthesis, and the pressure increases significantly with depth. Many creatures in this layer, such as squid, swordfish, wolffish, and lanternfish, have adapted to the dim environment through bioluminescence—the ability to produce their own light. This glow helps them attract prey or communicate in the darkness. Some species migrate upward at night to feed in the epipelagic zone and return to the depths by day. The mesopelagic zone plays an important role in transferring nutrients downward as organic matter from above sinks slowly through the water column.
The bathypelagic, or midnight zone, lies in total darkness, except for the faint light from bioluminescent organisms. The temperature is near freezing, and pressure is immense—over 400 times that at the surface. There are no plants here, as sunlight cannot reach these depths. Instead, organisms survive by feeding on “marine snow,” a constant drift of dead particles and organic debris from the upper zones. Species like the anglerfish, hatchetfish, and giant squid are found here, adapted with large mouths and expandable bodies to handle scarce food. Despite the harsh conditions, this zone remains surprisingly active with life specially evolved to endure cold and darkness.
The abyssopelagic zone, or abyssal zone, stretches from about 4,000 meters to just above the ocean floor. Conditions here are extremely cold, dark, and high in pressure, with temperatures near freezing. Sunlight never reaches this layer, and oxygen levels are low, yet some life persists. Creatures such as basket stars, sea cucumbers, sea spiders, and certain squid species have evolved to survive these conditions. Many are transparent, eyeless, or slow-moving to conserve energy. The seafloor in this region is shaped by volcanic ridges and hydrothermal vents that release minerals and heat, forming unique ecosystems that support bacteria and specialized organisms.
The hadopelagic, or hadal zone, is the deepest part of the ocean, found in narrow trenches and deep troughs that can reach depths of nearly 11,000 meters. Pressures here exceed 1,000 times that at the surface, and temperatures are influenced by adiabatic heating caused by the immense compression of water. Despite the extreme environment, a few hardy species live here, including worms, amphipods, echinoderms, and mollusks. These organisms are adapted to survive crushing pressure, total darkness, and scarce food. The hadal zone remains one of the least explored regions on Earth.