Coral reefs provide a habitat for a wide variety of life forms.
The oceans form a vast marine environment that covers more than 70% of the Earth’s surface. In this immense landscape, a wide variety of habitats are found, from tidal communities close to the coast to deep, cold ocean trenches long considered devoid of life. While not divided into biomes like terrestrial habitats, ocean habitat is divided into regions and habitats based on water depth and other characteristics. Two major divisions are coastal habitats, which range from the coast to the edge of the continental shelf, and the open ocean environment, encompassing the area that extends beyond the continental shelf. Within a vertical column of ocean water, habitats can be divided into near-surface pelagic and deep-water demersal habitats.
Because of the waves, underwater life near the ocean shore can be harsh.
While some of the same factors affect ocean habitat that affect terrestrial environments, many factors are unique to the marine environment. Wave action and tides can make the near-shore environment harsh, with widely varying conditions. Salinity ranges from estuary habitats, where salt water from the ocean combines with fresh water, to the more stable salinity of open ocean habitat. Currents affect temperature and food availability in many of the underwater habitats. The amount of light that penetrates the water determines whether phytoplankton and ocean plants can survive and form the basis of various food chains.
The amount of light that penetrates the ocean’s surface determines the type of plants and animals that live at certain depths.
Demersal or benthic habitats are found on the ocean floor. They are divided into shallow coastal benthic and deep ocean benthic habitats found beyond the continental shelf. Coral reefs are a benthic habitat in shallow, warm waters where an abundance of light penetrates. Known for its great biodiversity, this ocean habitat depends on coral colonies that build reefs. Within the reef, microenvironments are found supporting distinct communities in front of the reef, where wave action is greatest, and in the calmer areas behind the reef.
A very different type of benthic habitat is found in the abyssal plains of the ocean floor. Here, no light penetrates and plants are not found. The organisms that live in this oceanic habitat are primarily debris eaters, subsisting on organic matter that floats to the sea floor. Little studied due to the difficulties involved, it is believed that this deep area is rich in biodiversity. Chemosynthesis forms the basis of life in the unique environments found near cold springs and hydrothermal vents.
Kelp forests and anchored kelp beds exist in coastal areas where enough light penetrates the water to support plant life. These habitats are mostly found in the polar and temperate zones. Rich habitats that support diverse communities of marine creatures, kelp forests provide a vertical underwater environment. This ranges from the canopy at the surface to the benthic environment at the base of the kelp forest, each zone supporting a unique community of organisms. This ocean habitat has been extensively researched and is also economically important.