Open Ocean

The open ocean, also called the pelagic zone, is the biome of the water column beyond the continental shelf, extending from the sunlit surface down through progressively darker and colder layers to the deep sea floor. Unlike coastal and reef biomes, it offers no fixed substrate to live on, so its animals are either strong swimmers, such as tuna and whales, or drift with the currents as plankton; sunlight only penetrates the uppermost few hundred metres, so nearly all food in the deeper pelagic zone ultimately depends on organic matter sinking from that thin lit layer above. Covering the majority of the planet's surface, the open ocean is the largest biome on Earth by area, though its resources are far more sparsely and unevenly distributed than in a coastal or reef biome of comparable size.