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Important Facts on Marine Biomes

Earth's marine biomes were the origin of the planet's life, providing the aquatic habitat for the single-celled organisms which eventually evolved into more complex life forms. Earth's marine biomes cover approximately 75 percent of the planet's surface and consist of oceans, estuaries and coral reefs. Marine biomes sustain all life on Earth, providing much of the planet's oxygen through the photosynthetic processes of plankton and algae.

Euphotic Zone
- The euphotic zone consists of the ocean's upper waters, which receive enough sunlight to support photosynthesis and allow phytoplankton to thrive. This light absorption makes the euphotic zone the warmest and most hospitable ocean layer to life, supporting most of the ocean's marine mammals, fish and plant life. Phytoplankton describes a number of single-celled organisms such as diatoms, cyanobacteria and dinoflagellates. In addition to creating oxygen through photosynthesis, phytoplankton convert carbon dioxide into carbohydrates and are the primary food source for whales, fish and the ocean's larger zooplankton.
Benthic and Abyssal Zones
- The benthic zone is separated from the pelagic by a thermocline layer, a belt marking an abrupt transition from warm to frigid waters. Sunlight doesn't penetrate these waters, consigning them to perpetual darkness and making marine life uncommon at this depth. The abyssal zone contains the deepest ocean waters, with deep-sea life that clusters around geothermal vents embedded in the ocean floor. These vents release a chemical soup that can support micro-organisms and the larger organisms that prey upon them, such as sea worms, arthropods and fish equipped to withstand the crushing pressures of these depths.
Estuaries
- Estuaries mark the juncture where Earth's freshwater and marine biomes meet, and estuary types such as river mouths, marshes and lagoons contain a mix of fresh and salt water. Estuary water salinity varies considerably depending on tidal action, rainfall and freshwater flow into the estuary. The water is typically murky due to the large sediment volume deposited into the estuary by rivers and streams. Organic matter within the sediment that sinks to the bottom is decomposed by bacteria, a process that consumes a great deal of oxygen, making the deeper waters inhospitable for larger forms of marine life.
Coral Reefs
- Corals, algae and other organisms produce calcium carbonate and silica to construct the reef's vast structure, which provide a home for polyps that affix themselves to the reef and extend tentacles to snare their prey. Coral reefs are also habitats for octopi, shellfish and starfish, and the phytoplankton and algae living within the corals produce the oxygen necessary to sustain its marine life. Coral reefs can only survive in brightly lit, highly oxygenated environments and are only found within shallow waters, typically running parallel to continental land masses or encircling islands.

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