Planèt'eau > Oceans > 2 - About ocean's diversity
2 - About ocean's diversity
The rolling waves, glassy stillness, or frosty ice we see on the ocean’s surface hide an amazing variety of underwater worlds - from sunlit coral reefs to dark abyssal canyons, from forests of giant kelp to mussel communities clustered around scorching hydrothermal vents, from tidal mangroves to the vast open ocean.
Discover some of the ocean's secrets :
2.a. Coasts
The coastal zone - such as tropical coral reefs, seagrass meadows, mangrove forests, and kelp forests - makes up only 10% of the ocean environment, but is home to over 90% of all marine species. For example, of the 13,200 known species of marine fish, almost 80% are coastal.
The coastal zone has the most nutrients of all marine environments. Sunlight can penetrate the shallow waters above continental shelves (land that slopes gently down from the coastline of most continents to a depth of around 200m) meaning that plants can grow, while the sea floor provides an anchor for many organisms. As a result, a number of extremely productive and complex coastal ecosystems have evolved.
Not only do these ecosystems support a huge variety of life, many also serve as nurseries for much of the biodiversity of the entire oceanic system. These ecosystems also help protect coastal land from erosion due to storm surges and other large waves, such as tsunamis.
The coast also has a huge influence on people. According to the UN, around 3.6 billion people, or 60% of the world’s population, live within 60km of the coast. And 80% of all tourism takes place in coastal areas. Most of the goods we extract from the ocean - from fish to oil and gas - come from coastal regions. Coastal ecosystems also provide a range of services that benefit people around the world.
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Sally lightfoot crab on Galapagos Islands Ecuador
2.b. Open oceans
Even it might look uniform from the air, but the open ocean is extremely varied. The open ocean is enormous. Also called the pelagic zone, it includes all the world’s oceans except for coastal waters and the sea floor.
Pelagic waters are not all the same. Some areas are teeming with life, while others are nearly lifeless. Enormously long currents flow like rivers under the surface, influencing everything from the concentration of marine life to weather systems on land. There’s also a huge 'vertical' variety, from sunlit surface waters down through the twilight zone to almost complete darkness and crushing pressures below 1000 m.
Despite its vastness, only around 10% of all marine species live in the open ocean. But these include the world’s biggest, fastest, deepest diving, furthest travelling ... and, to our eyes, most alien-looking animals. And some of these are of immense commercial value to people.
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Bigeye trevalli in Fiji
2.c. Deep seas
60% of our planet is covered by water over 1,600m deep, and nearly half the world's marine waters are over 3,000m deep.
The deep sea starts where the sunlight starts to fade, around 200m below the surface of the ocean. A twilight zone extends down to 1,000m, after which almost no light penetrates. The water is cold, reaching 3ºC, and contains very little oxygen. And the weight of the water above creates enormous pressures, up to 1,000 times that at the surface.
With no sunlight, plants cannot grow in the deep sea. And while animals and bacteria have been found wherever people have looked, we know very little about these dark, cold depths. More people have travelled into space than have ventured into the deep.
The deep sea is home to weird and wonderful creatures and a variety of habitats, from abyssal plains to hydrothermal vents to underwater mountains covered in cold-water coral.
Incredible biological discoveries have been made in the last 30 years. These include entire new ecosystems such as cold-water coral reefs and vibrant communities based around chemicals pouring from the Earth's crust, as well as a whole host of alien-looking fish and other animals. Scientists now think there may be more species in the deep sea than in all the other environments on Earth combined - by some estimates, as many as 100 million species may live there.
The deep sea is beyond most people's direct experience - but you may be more familiar with some of its creatures than you think. Fishers are increasingly targeting deep-water fisheries around the world.
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Amphipod resting on a deep sea coral Throndheim Fjord Norway