Marine ecosystem

Introduction
Origins of marine life
The marine environment
- Geography, oceanography, and topography
- Physical and chemical properties of seawater
- Ocean currents
Marine biota
- Plankton
- Nekton
- Benthos
- Links between the pelagic environments and the benthos
- Organisms of the deep-sea vents
Patterns and processes influencing the structure of marine assemblages
- Distribution and dispersal
- Migrations of marine organisms
- Dynamics of populations and assemblages
Biological productivity
- The pelagic food chain
- Upwelling
- Seasonal cycles of production

References & Edit History Quick Facts & Related Topics

Images & Videos

Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters.

Diagram showing the cycling of silica in the marine environment, with arrows illustrating processes such as river influx, inorganic adsorption, biological fixation by radiolarian and diatom skeletons, dissolution, deposition as opaline skeletal debris, upwelling, and hydrothermal activity, all within labeled ocean zones.

A diagram of a generalized aquatic food web shows various marine organisms connected by arrows indicating predator-prey relationships. Top predators like large sharks, smaller sharks, and marlin are at the top, followed by predators such as tuna, squid, lancet fish, and mackerel. Filterers like lantern fish, amphipods, and ocean sunfish occupy the next level, with zooplankton such as shrimp, copepods, and pteropods below them. At the base, phytoplankton including dinoflagellates and diatoms prov

Clusters of hydrothermal mussels with white Galatheid crabs and shrimp grazing on bacterial filaments near a deep sea vent at the Northwest Eifuku submarine volcano in the Mariana Trench.

Illustration comparing a complex ocean food web, with interconnected feeding relationships among marine animals and plankton, to a simple linear food chain showing energy flow from sun to producers, primary consumers, and up to top predators.

Two diagrams compare coastal upwelling during normal conditions and an El Nino event. The top shows strong upwelling with nutrient-rich water and high plankton near the coast, while the bottom shows weak upwelling, a thicker nutrient-poor surface layer, and reduced plankton during El Nino.

Illustration of an ocean food chain showing sunlight supporting one-celled life like dinoflagellates and diatoms, which are eaten by shrimplike copepods. These are consumed by small fish, which are then eaten by mackerel, followed by tuna, and finally a large shark at the top of the food web.

Learn about microplastic and its harmful effect on marine animals

Quizzes

Chutes d'Ekom - a waterfall on the Nkam river in the rainforest near Melong, in the western highlands of Cameroon in Africa.

Ecosystems

Related Questions

How are marine organisms affected by ocean currents?
How can large jellyfish populations reduce fish populations in enclosed seas?
How can ocean acidification disrupt marine food chains?
How can pollutants become more concentrated at higher levels of marine food chains?
How can the order in which organisms colonize an intertidal reef change the community that develops there?
How do changes in salinity affect marine organisms living in estuaries?
How do deep-sea animals use bioluminescence to find prey or avoid predators?
How do fertilizer runoff and untreated sewage change coastal marine ecosystems?
How do fish and cephalopods achieve neutral buoyancy in seawater?
How do food webs show more feeding relationships than single food chains?
How do hurricanes alter coral reef communities and their recovery?
How do hydrothermal vents support ecosystems without sunlight?
How do ice ages cause sea levels to fall?
How do mangrove roots protect coastlines and improve water quality?
How do marine animals form mutualistic relationships with bacteria near hydrothermal vents?
How do meroplankton and holoplankton differ over their life cycles?
How do mid-ocean ridges create new oceanic crust?
How do nutrients control phytoplankton growth in coastal waters?
How do ocean currents and food supplies affect the survival of marine larvae?
How do oil spills harm phytoplankton and zooplankton in marine ecosystems?
How do organisms such as tripod fish survive in permanent deep-sea darkness?
How do pelagic organisms provide food for benthic animals?
How do phytoplankton and zooplankton differ in marine food webs?
How do river runoff and sediments affect organisms on the continental shelf?
How do salmon and eels control salt levels in their bodies when moving between fresh water and seawater?
How do some dinoflagellates obtain food without relying only on photosynthesis?
How do sulfur-oxidizing bacteria provide energy for organisms near hydrothermal vents?
How does Earth’s rotation influence ocean currents through the Coriolis effect?
How does marine snow provide food for animals on the ocean floor?
How does the euphotic zone support photosynthesis in the ocean?
Which human activities threaten mangrove forests?
Which marine animals migrate from the aphotic zone to the photic zone at night?
Why are many tropical surface waters less productive than colder ocean waters?
Why are plankton important to marine food chains?
Why can larval crabs and lobsters look very different from adult animals?
Why can ocean acidification threaten cold-water coral communities at great depths?
Why do waters above continental shelves often contain more nutrients than open-ocean waters?
Why does photosynthesis stop below certain depths in the ocean?
Why does upwelling make some ocean regions highly productive for fisheries?
Why is less energy available to organisms at higher trophic levels in a marine food chain?
Why was the Great Barrier Reef’s continental shelf above sea level during the last Pleistocene Ice Age?

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External Websites

Defenders of Wildlife - Basic Facts About Marine Habitats
National Center for Biotechnology Information - Recovery of Marine Ecosystems
ABC listen - Ockham's Razor - Understanding change in marine ecosystems: a grand challenge for science
Science Learning Hub - Marine ecosystem

Marine ecosystem

ecology

Also known as: ocean ecosystem, sea ecosystem

Written by

Michael John Kingsford

Professor and Head of the School of Marine Biology and Aquaculture, James Cook University, Queensland, Australia.

Michael John Kingsford

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 12, 2026 •History

Marine ecosystem, complex of living organisms in the ocean environment. Marine waters cover two-thirds of the surface of the Earth. In some places the ocean is deeper than Mount Everest is high; for example, the Mariana Trench and the Tonga Trench in the western part of the Pacific Ocean reach depths in excess of 10,000 metres (32,800 feet). Within this ocean habitat live a wide variety of organisms that have evolved in response to various...

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