Marine Ecosystem
A marine ecosystem is a community of living organisms — including phytoplankton, zooplankton, fish, marine mammals, and benthic organisms — interacting with each other and their physical environment (water, light, temperature, salinity, nutrients) in the ocean. Marine ecosystems range from shallow coastal zones and estuaries to the open pelagic ocean, deep-sea hydrothermal vents, and polar seas, with each zone characterized by distinct biological communities adapted to its conditions. These ecosystems provide critical services including oxygen production (phytoplankton generate ~50% of Earth's oxygen), carbon sequestration, food security for billions of people, and climate regulation.
Major Marine Ecosystem Zones and Their Characteristics
| Zone | Depth | Light | Primary Producers | Representative Species |
|---|---|---|---|---|
| Intertidal zone | 0 m (shoreline) | Full sunlight | Algae, seagrass | Barnacles, mussels, crabs |
| Neritic zone | 0–200 m | Photic zone | Phytoplankton, kelp | Herring, cod, dolphins |
| Pelagic zone | 200–3700 m | Decreasing with depth | Phytoplankton (upper) | Tuna, sharks, squid |
| Bathypelagic zone | 1000–4000 m | No sunlight | Chemotrophs (vents) | Anglerfish, viperfish |
| Abyssal zone | 4000–6000 m | None | Bacteria, detritus | Sea cucumbers, brittle stars |
| Hadal zone | >6000 m (trenches) | None | Bacteria | Amphipods, snailfish |
Interactive Tools
NOAA National Marine Sanctuaries
Educational resources and data on US marine ecosystem biodiversity and conservation
Open ToolOcean Biodiversity Information System
Global database of marine species distribution and biodiversity records
Open ToolKhan Academy: Marine Ecosystems
Overview of marine ecosystem types, food webs, and the impact of human activities
Open Tool
Wikimedia Commons, CC BY-SA
Related Terms
Coral Reef
A coral reef is an underwater ecosystem built by colonies of tiny marine animals called coral polyps, which secrete calcium carbonate (CaCO₃) to form hard, branching skeletons that accumulate over thousands of years into complex three-dimensional reef structures. Coral reefs require warm (23–29°C), clear, shallow, sunlit waters with normal marine salinity, as the polyps depend on photosynthetic algae called zooxanthellae living symbiotically within their tissues. Coral reefs cover less than 1% of the ocean floor yet support approximately 25% of all known marine species, making them the most biodiverse marine ecosystems on Earth.
Ocean Salinity
Ocean salinity is the concentration of dissolved salts in seawater, primarily sodium chloride (NaCl), along with chloride, sulfate, magnesium, calcium, and potassium ions. Average ocean salinity is approximately 35 parts per thousand (ppt) or 35 g of salt per kilogram of seawater, though it varies regionally due to evaporation, precipitation, river input, sea ice formation, and melting. Salinity directly affects seawater density and is a key driver of thermohaline circulation, marine organism physiology, and the freezing point of seawater.
Coastal Upwelling
Coastal upwelling is an oceanographic phenomenon in which wind-driven surface water is pushed away from the coast, causing cold, nutrient-rich water from deeper ocean layers to rise and replace it at the surface. This process is driven by the combined effects of prevailing winds blowing parallel to the coastline and the Coriolis effect, which deflects the surface water offshore — a process described by Ekman transport. Coastal upwelling regions are among the most biologically productive ocean areas on Earth, supporting major fisheries such as those off Peru, California, and West Africa.
From Greek "marinus" (of the sea, from "mare" meaning sea) and "oikos" (house, dwelling) + "systema" (organized whole). The term "ecosystem" was coined by British ecologist Arthur Tansley in 1935. The systematic study of marine ecosystems accelerated with the Challenger expedition (1872–1876) and has grown with satellite oceanography in the modern era.