The oceans form a vast marine environment that covers more than 70 percent of the earth’s surface. Within this immense environment is a wide range of habitats, from tidal communities near the coast to deep, cold ocean trenches, considered for a long time lifeless. Although it is not divided into biomes like terrestrial habitats, oceanic habitat is divided into regions and habitats based on water depth and other characteristics. Two major divisions are coastal habitats, which extend from the coast to the edge of the continental shelf, and the open oceanic environment, which encompasses the area extending beyond the continental shelf. In a vertical column of ocean water, habitats can be divided into near-surface pelagic habitats and deep-water demersal habitats.
While some of the same factors affect oceanic habitat that affect terrestrial environments, many factors are unique to the marine environment. The action of waves and tides can hinder the environment close to the coast with very variable conditions. Salinity ranges from estuarine habitats where salt water from the ocean combines with fresh water to the most stable salinity of open ocean habitat. Currents affect temperature and food availability in many underwater habitats. The amount of light that enters the water determines whether phytoplankton and ocean plants can survive and form the basis of various food chains.
Demersal or benthic habitats are found at the bottom of the oceans. They are divided into shallower coastal benthic habitats and deep oceanic benthic habitats that lie beyond the continental shelf. Coral reefs are benthic habitat in warm, shallow water where much light enters. Known for its great biodiversity, this oceanic habitat depends on coral colonies that build reefs. Within the reef, there are microenvironments that support different communities at the front of the reef where the action of the waves is strongest and in the quieter areas behind the reef.
A very different type of benthic habitat is found in the abyssal plains of the deep ocean floor. No light enters here and the plants are not found. The organisms that live in this oceanic habitat are mainly debris eaters, which live on the organic matter that floats on the seabed. Little studied by the difficulties encountered, this deep area is considered rich in biodiversity. Chemosynthesis forms the basis of life in unique environments that are close to cold leaks and hydrothermal vents.
Kelp forests and anchored kelp beds exist in coastal areas where enough light enters the water to sustain plant life. These habitats are found mainly in the polar and temperate zones. Rich habitats that support diverse communities of sea creatures, algae forests provide a vertical underwater environment. This ranges from the canopy to the surface to the benthic environment at the base of the algae forest, each area supporting a unique community of organisms. This oceanic habitat has been extensively researched and is also economically important.