Marine Biomes

The ocean is the largest marine biome. It is a continuous body of salt water that is relatively uniform in chemical composition; it is a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second kind of marine biome. Estuaries, coastal areas where salt water and fresh water mix, form a third unique marine biome.


The largest of all the ecosystems, oceans are very large bodies of water that dominate the Earth’s surface. Like ponds and lakes, the ocean regions are separated into separate zones: intertidal, pelagic, abyssal, and benthic. All four zones have a great diversity of species. Some say that the ocean contains the richest diversity of species even though it contains fewer species than there are on land.

The ocean is categorized by several areas or zones.

  • All of the ocean’s open water is referred to as the pelagic realm (or zone).
  • Within the pelagic realm is the photic zone, which is the portion of the ocean that light can penetrate (approximately 200 m or 650 ft). At depths greater than 200 m, light cannot penetrate; thus, this is referred to as the aphotic zone. The majority of the ocean is aphotic and lacks sufficient light for photosynthesis.
  • The benthic realm (or zone) extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor.
  • The deepest part of the ocean, the Challenger Deep (in the Mariana Trench, located in the western Pacific Ocean), is about 11,000 m (about 6.8 mi) deep.

Coral Reefs

Coral reefs are ocean ridges formed by marine invertebrates living in warm shallow waters within the photic zone of the ocean. They are found within 30˚ north and south of the equator. The Great Barrier Reef is a well-known reef system located several miles off the northeastern coast of Australia. Other coral reef systems are fringing islands, which are directly adjacent to land, or atolls, which are circular reef systems surrounding a former landmass that is now underwater. The coral organisms (members of phylum Cnidaria) are colonies of saltwater polyps that secrete a calcium carbonate skeleton.


Estuaries are areas where freshwater streams or rivers merge with the ocean. This mixing of waters with such different salt concentrations creates a very interesting and unique ecosystem. Microflora like algae, and macroflora, such as seaweeds, marsh grasses, and mangrove trees (only in the tropics), can be found here. Estuaries support a diverse fauna, including a variety of worms, oysters, crabs, and waterfowl.


  • abyssal zone: the deepest part of the ocean at depths of 4000 m or greater
  • algal bloom: a rapid increase of algae in an aquatic system
  • aphotic zone: the part of the ocean where photosynthesis cannot occur
  • benthic realm: (also, benthic zone) the part of the ocean that extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor
  • channel: the bed and banks of a river or stream
  • coral reef: an ocean ridge formed by marine invertebrates living in warm shallow waters within the photic zone
  • cryptofauna: the invertebrates found within the calcium carbonate substrate of coral reefs
  • ecosystem services: the human benefits provided by natural ecosystems
  • emergent vegetation: the plants living in bodies of water that are rooted in the soil but have portions of leaves, stems, and flowers extending above the water’s surface
  • estuary: a region where fresh water and salt water mix where a river discharges into an ocean or sea
  • intertidal zone: the part of the ocean that is closest to land; parts extend above the water at low tide
  • neritic zone: the part of the ocean that extends from low tide to the edge of the continental shelf
  • oceanic zone: the part of the ocean that begins offshore where the water measures 200 m deep or deeper
  • pelagic realm: (also, pelagic zone) the open ocean waters that are not close to the bottom or near the shore
  • photic zone: the upper layer of ocean water in which photosynthesis is able to take place
  • planktivore: an animal that eats plankton
  • source water: the point of origin of a river or stream
  • wetland: environment in which the soil is either permanently or periodically saturated with water

Leave a Reply

Your email address will not be published. Required fields are marked *