Dolphins can be found on continental shelves.
Contrary to popular belief, most of the seafloor, known as the “open ocean,” is not really a habitat for animals, but rather a place they pass through on their way to somewhere else. In most of the world, the ocean floor is very deep, with an average depth of 3,790 meters (12,430 feet). Nearly half of the world’s seafloor is more than 3,000 meters (9,800 feet) deep. In total, the seafloor makes up around 71% of the world’s oceans, with shallow waters such as continental shelves making up 29%.
Jellyfish live at the bottom of the sea.
Animal life at the bottom of the sea is very different depending on whether it is the continental shelf or the deep ocean. The continental shelves are where the greatest biodiversity is found. Many plants and animals live here: kelp forests, large amounts of algae, sharks, fish, crustaceans, brachiopods, bivalves, sponges, cnidarians (jellyfish and allies), echinoderms (starfish, sea urchins and allies), cetaceans (whales, dolphins, porpoises) and many more. Of the 38 animal phyla, all but one, the velvet worms, have a marine version. This is why the field of marine biology is so large.
Bioluminescent jellyfish produce their own light and are most often found in the aphotic zone of the ocean.
Although continental shelves are technically the “bottom of the sea,” sometimes when the word is used, it refers specifically to the bottom of the sea. The deep sea is almost completely devoid of life, as the aphotic (lightless) zone of the ocean begins at a depth of 0.9 km (15,000 ft) and continues to the bottom. As the lightless regions cannot support plants or photosynthetic bacteria, the ecosystem in the aphotic zone depends mainly on organic debris falling from above. Many animals that are in the aphotic zone are capable of producing their own light, called bioluminescence.
Starfish call the ocean floor home.
At the bottom of the deep sea, an area less than 1% of which has been explored by humanity, key ecosystems are built around seamounts, where animals tend to congregate, and cracked valleys, where geological activity can provide warmth. and chemicals to sustain a mini-ecosystem. Two famous deep-sea ecosystems are those built around hydrothermal vents and cold springs. None of these ecosystems depend on the sun for energy. The producers of these ecosystems are chemotrophic bacteria, which oxidize inorganic chemical substances to obtain energy.
The most abundant animals on the seabed are probably nematodes, also known as flatworms. They have an average size of 1 mm and can be found in the deepest trenches of the ocean, where the pressure exceeds 1,000 atmospheres. Echinoderms (starfish and relatives) can also be found on the ocean floor, as can fish such as flounder and plaice. The shrimp was reportedly present at the bottom of the Mariana Trench, the deepest ocean trench on the planet. One strange creature found at the bottom of the ocean is the giant isopod, which looks similar to a wood louse but can be a foot long.