Some of the animals that swim in the sunlit surface waters of the ocean, or live on the seabed in shallow waters. Although the oceans make up by far the largest biome on Earth, only about 20% of Earth’s species live in the oceans, of which about 90% are bottom-living, shallow-water species. With the abundance of microscopic plants in sunlit, shallow waters, taken together with nutrients washed out to sea from the land or brought to the surface by upwelling currents, coastal marine life is by far the most abundant of all ocean habitats. In the rest of the ocean, especially the zone below a depth of 1000 metres (3300 feet) where no light penetrates at all, life is extremely sparse.
There are two main ocean habitats: the water itself, the pelagic habitat, and the ocean floor, the benthic habitat. Both are divided into several zones, according to the amount of sunlight that reaches down through the water. Most life is concentrated in the upper 200 metres (660 feet) in the relatively shallow waters of the continental shelf, where plankton, a rich source of food, is plentiful.
Plankton seen through a microscope
Only about 5% of ocean waters have been explored.
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