The Habitats in the Ocean

The ocean provides a variety of habitats where marine organisms can thrive. An ocean habitat is the environment where a number of organisms can live.  Ocean habitats are usually divided into two distinct habitats; the coastal habitat and the open ocean habitat. Within these marine habitats, there are other smaller habitats, all of them providing a home for certain species of marine plants and animals. Some marine organisms depend so much on one another, such that they may form mutualistic relationships among them, with the larger organisms providing a habitat to a smaller organism, such as in a symbiotic relationship. The ocean provides various habitats, some of them close to the coast and others far away from the coast.

The coastal habitat

A wide variety of marine organisms are found along the coast. The coast contains a number of habitats (life zones), all of them, with distinct species of animals. Coastal habitats extend from the point where the high tide reaches the coast to as far as the limits of the continental shelf, usually 70 km (43 miles) on average away from the coast. The coastal environment provides the habitat for a wide variety of organisms, including crustaceans, mollusks, sand shrimp, spider crabs, worms, snails, sea stars, shellfish, turtles, sponges, sandpipers, pelicans, barnacles and fish. In the coastal habitat, it is customary to find shrubs, grasses and trees, as well as rockweed and seaweed, which is carried to the coast during a high tide.

Estuary habitat

Estuaries, also known as the nurseries of the sea, are some of the most biologically rich habitats in the planet. An estuary is a coastal body of water where fresh water and ocean salty water converge, creating nutrient-rich water and soil. Phytoplankton are the primary producer organisms in estuaries, moving in and out of the estuaries by the continuous flux of ocean tides. Estuaries provide habitat for a great variety of invertebrates, mammals, birds and fish. Within estuaries, there are other habitats, including mangrove forests, salty marshes, sea grass meadows, river deltas, sandy beaches, rocky shores, salt and fresh water marshes and mud flats, all of them with their own diversity of life.

Kelp forests

Kelp forests are under water habitats that provide the ideal environment for a great variety of marine life. Kelp forests occur where there is an abundance of nutrients, hard substrate to which kelp can attach and sufficient light. Kelp thrives best where there is a high level of nutrients, such as those found in upwelling regions, where deep ocean waters bring nutrients to the ocean’s surface layer. Giant kelp can grow from 30-60 cm (11.8-23.6 inches) a day, given there is sufficient light penetration in the water column. The marine environment created by kelp forests provides the habitat for a great variety of organisms. The organisms thriving in the kelp habitat can further create the right habitat for other marine species.

Sea grass meadows

This habitat grows in large meadows, resembling those of grassland. Sea grass meadows need sunlight for photosynthesis, thus, they thrive in the photic zone, near shallow coastal waters. Sea grass meadows provide the habitat for many species of fish, micro and macroalgae, mollusks, bristle worms and nematodes. Sea grass is an important source of food in the aquatic food chain. Many marine species, such as turtles, manatees, crabs, sea urchins, geese, and fish, feed on sea grass meadows, Sea grasses provide protection to coastal communities against the power of ocean waves, and coastal erosion.

Continental shelf

A continental shelf is the region in the ocean, extending for about 70 km (43 miles) beyond the coastline. The continental shelf is on average less than 200 meters (656 ft.) deep and it provides the right conditions for photosynthetic organisms, such as phytoplankton, to survive. Phytoplankton are microscopic marine plants that form the base of the marine food web. Typically, continental shelves are rich in nutrients from both, land runoff into coastal waters and upwelling of nutrients from the deep ocean. Most phytoplankton often forms algal blooms in these rich-nutrient waters; however, the continental shelf can be subjected to tides, storms and currents, carrying a whole habitat within them.

Ocean currents

When the population of phytoplankton has become denser in an ocean current, the current becomes the right habitat for other marine organisms, such as zooplankton.  Zooplankton, which are marine animals, feed on phytoplankton. After zooplankton has populated their habitat in the water current, the current begins to be inhabited by other organisms, such as fish that feed on them, and soon other organisms move into the habitat, such as larger predatory fish, and even larger marine animals, including whales and sharks. Over time, the current can become a drifting habitat for a wide variety of marine life.

Coral reef habitat

Coral reefs are amongst the most diverse habitats in the world. Coral reefs are marine structures made of calcium carbonate that is secreted by corals. They provide the habitat to approximately ¼ of the world’s marine species. Coral reefs are found most commonly in the tropical waters of the world, where ocean water is clear and shallow, allowing the penetration of sunlight for the reproduction of zooxanthellae, the microalgae that grows within the coral polyps, which is responsible for the building of coral reefs. Coral reefs support a wide variety of marine organisms, including fish, sea stars, sea urchins, clown fish, crabs, flatworms, shrimps, parrotfish, butterfly fish, triggerfish, moray eel, angelfish, sponges, anemones, zooplankton, algae and bacteria.

Open Ocean

The open ocean habitat comprises the region beyond the continental shelf, and can be divided into the pelagic habitat and the demersal habitat. The pelagic habitat is that one found on the water column, including the surface of the ocean, but not the bottom, while the demersal habitat if found near or on the bottom of the ocean. Pelagic habitats depend on the ocean currents behavior for nutrients; therefore, pelagic habitats can be short-lived. Unlike the coastal habitat, the ocean habitat is not as rich in nutrients; therefore the ocean ecosystem depends on the nutrients, much of which come from land runoff as dissolved nutrients. It is estimated that only 10 percent of marine life live in the open ocean.

Pelagic habitat

The ocean water contained in the first 200 meters (656 ft.) comprises the epipelagic zone. This is the zone where enough sunlight must enter allow photosynthetic organisms to thrive. Most habitats only form in rich-nutrient waters, such as those near the continental shelves, where nutrients usually are brought up from the deep ocean or are distributed by the ocean’s currents. Given there are enough nutrients and sunlight penetration, phytoplankton are the first organisms to multiply, turning the ocean water into a greenish water and forming the base of a food chain in which larger organisms feed, including seabirds, fish, sardines, whale sharks, manta rays, squid, dolphins and toothed whales, among many others.

Deeper beyond the epipelagic zone are other habitats, each supporting different kinds of marine organisms. The aphotic zone, which is where sunlight is unable to penetrate, can be divided into the mesopelagic, bathypelagic an abyssopelagic layers. The majority of nutrients needed by organisms living in these layers fall from above the ocean in the form of detritus (dead remains of marine animals). Most organic matter is consumed by microbes, zooplankton, and other organisms within the epipelagic zone. Due to the lack of sunlight in these zones, many organisms have developed bioluminescence, such as the lantern fish,

Sea floor habitat

Another type of life form exists in the deep ocean floor, where extreme pressures and the lack of sunlight might suggest the contrary. Hydrothermal vents are fissures in the sea floor crust where heated water emerges, creating the habitat for complex marine communities which are able to survive due to the chemicals dissolved in their fluids. Many new microbes and other life forms have been discovered in hydrothermal vents. Chemosynthetic bacteria are at the base of the food chain in this habitat, supporting larger organisms, including giant tube worms, limpets, clams and shrimp.

The ocean is very diverse and it hosts a wide variety of living organisms. While the smallest organisms inhabit the coastal ecosystem, the largest animals inhabit the open ocean waters, and might come as close as the continental shelves to feed on phytoplankton, creating ephemeral habitats within that region of the ocean. According to, the oceans have unique habitats that are not like those found on freshwater bodies.