Abyssopelagic

Abyssopelagic, or the abyssopelagic zone, is the deepest layer of the pelagic ocean. It lies roughly from 4,000 to 6,000 meters below the surface, with some classifications extending into the hadalpelagic zones found in deep trenches. The environment is characterized by perpetual darkness, near-freezing temperatures around 2–3 °C, and very high hydrostatic pressure, typically about 400–600 atmospheres.

Nutrient input is limited, and food comes mainly from falling marine snow, dead organisms, and occasional currents that transport organic matter from upper layers. Most abyssopelagic regions lack sunlight and plant life; primary production is virtually absent, and ecosystems rely on detritus-supported communities and, where present, hydrothermal or cold seep habitats that can supply energy through chemosynthesis.

Organisms living here are adapted to extreme pressure, cold, and scarce food. Common groups include crustaceans such as amphipods and isopods, echinoderms like holothurians and brittle stars, polychaete worms, and various slow-moving fishes such as rattails (grenadiers), cusk-eels, and deep-sea anglerfishes. Many species have large mouths and expandable stomachs to maximize food intake, reduced skeletal structures, and enzymes adapted to high pressure. Bioluminescence occurs in some abyssopelagic species, though not as universally as in shallower zones.

Due to the extreme conditions, abyssopelagic life is studied mainly through deep-sea sampling with submersibles and remotely operated vehicles, revealing a diverse but sparsely populated community with notable regional differences across ocean basins.