The deep sea includes the bathypelagic and abyssal zones. Because of its depth and associated light deprivation, the bathypelagic zone is also known as the midnight zone. Virtually no sunlight penetrates into the ocean at these depths. As such, the animals that live here are bioluminescent. This adaptation is the result of low predator density and reduced visibility. Without any appreciable sunlight, the bathypelagic zone lacks photosynthetic plants and primary productivity. Species present in this zone are limited to: (a) Detrivores who feed on the downward drizzle of moulted exoskeletons, mucus sheets, fecal pellets, organism corpses and other organic debris falling from the mesopelagic zone; (b) Resident carnivores; or (c) other resident scavengers.
In the abyssal zone, water is very cold (around 3° C), highlypressured, high inoxygencontent, but low in nutritional content. The abyssal zone supports many species of invertebrates and fishes. Mid-ocean ridges (spreading zones betweentectonic plates), often with hydrothermal vents, are found in the abyssal zones along the ocean floors. Chemosynthetic bacteria thrive near these vents because of the large amounts of hydrogen sulfide and other minerals they emit. These bacteria are thus the start of thefood webas they are eaten by invertebrates and fishes. These bacteria thus allow a thriving ecosystem to exist in this tough environment.