Coral reefs, the so-called "rainforests of the sea"

A large proportion of all life on Earth exists in the oceans, which provide about 300 times as much habitable volume as terrestrial habitats. Marine habitats range from surface water to the deepest oceanic trenches, including coral reefs, kelp forests, seagrass meadows, tidepools, muddy, sandy and rocky seabeds, and the open pelagic zone. The organisms living in the sea range from microscopic phytoplankton and zooplankton to whales up to 30 metres (100 ft) long. Marine life is economically important to humans, especially the fish used for food, and provides support for the carbon cycle.[41][42]

Life probably originated in the sea and all the major groups of animals are represented there. Scientists differ as to in which part of the sea life arose: the Miller-Urey experiments suggested a dilute chemical "soup" in open water, but more recent suggestions include volcanic hot springs, fine-grained clay sediments, or deep-sea "black smoker" vents, all of which would have provided protection from damaging ultraviolet radiation which was not blocked by the early earth's atmosphere.[43]

Marine habitats[edit source | editbeta]

Main article: Marine habitats
Marine habitats can be divided (horizontally) into coastal and open ocean habitats. Coastal habitats extend from the shoreline to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only 7 percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf. Alternatively, marine habitats can be divided (vertically) into pelagic (open water), demersal (just above the seabed) and benthic (sea bottom) habitats. A third division is by latitude: from polar seas with ice shelves, sea ice and icebergs, to temperate and tropical waters.[42][44]

Coral reefs, the so-called "rainforests of the sea", occupy less than 0.1 percent of the world's ocean surface, yet their ecosystems include 25 percent of all marine species.[45] The best-known are tropical coral reefs such as Australia's Great Barrier Reef, but cold water reefs harbour a wide array of species including corals (only six of which contribute to reef formation)

Categories: