Deep Sea
Earth's Largest and Least Explored Ecosystem
The deep sea is the largest and most mysterious ecosystem on Earth, stretching thousands of meters below the ocean’s surface. Despite covering more than half (66%) of the planet, this dark, cold, high-pressure world remains largely unexplored. Scientists estimate that only 0.001% of the seafloor below 200 meters has been observed by humans.
At MarAlliance, we study the deep sea to reveal its biodiversity and ensure that even the most remote marine life is included in global conservation efforts. Our research focuses on the nearshore deep waters from around 200 to 500 meters, which are accessible to small-scale fishers. This depth zone holds remarkable biodiversity, including commercially important species of groupers and snappers, and more than a dozen species of sharks. Most species that live deeper than 200 meters migrate daily to shallower waters, including long-lived sharks, putting them at risk from fisheries and habitat destruction. Our research aims to shed light on this mostly unknown environment.
What Is the Deep Sea?
Life in the Deep Ocean: Adaptations for Extreme Conditions
Surviving Without Sunlight
Below 200 meters, light is scarce. By 1,000 meters, it’s completely dark, a zone often referred to as the midnight zone. Without sunlight, deep-sea animals rely on other strategies to find food and communicate.
Many species use bioluminescence, a chemical process that produces light. This glowing adaptation helps animals:
- Camouflage against faint light from above
- Attract prey with glowing lures
- Communicate to other animals or confuse predators
Bioluminescent organisms like jellyfish, squid, lanternsharks, and lanternfish make the deep sea come alive with flickers of blue and green light.
Adapting to Crushing Pressure
At the average depth of 4,000 meters, and much deeper in ocean trenches, pressure is hundreds to over a thousand times greater than at sea level. To survive:
- Many species have large eyes to maximize their vision in near total darkness. Yellow filtering pigments and lenses likely enhance contrast with ambient daylight.
- Deep-sea species have flexible cell membranes and pressure-tolerant proteins
- Some produce unique molecules that stabilize their bodies under stress
- Many species can’t survive in shallower waters due to these specialized adaptations
- Temperatures below 200 meters drop quickly. Many deep-sea species thrive at cold temperature thresholds and cannot tolerate warmer waters
From ghostly deep-sea sharks to gelatinous fish, evolution has shaped a range of creatures found nowhere else on Earth.
Deep-sea habitats are vulnerable to threats like deep-sea mining, overfishing, pollution, and climate change. With so much of this realm still undiscovered, protecting this delicate ecosystem before it's exploited is essential for global ocean health.
How Deep-Sea Ecosystems Work?
Oxygen Levels and Ocean Currents
Though mostly cut off from sunlight, the deep ocean often has enough oxygen to support life. This is thanks to global deep-sea currents, sometimes called the ocean conveyor belt, that transport cold, oxygen-rich water from polar regions into the ocean’s depths.
However, oxygen minimum zones (OMZs) exist between 500 and 1,000 meters deep. These areas are low in oxygen due to poor circulation and no photosynthesis. Life here is rare and uniquely adapted to survive under extreme stress.
And yet, many species thrive in this environment, and even move easily between the OMZ and more oxygen-rich waters.
Finding Food in the Deep
Without plants or sunlight, food in the deep sea is limited. Many organisms survive on:
- Marine snow: a constant rain of dead plankton, fecal matter, and organic particles falling from the surface
- Whale falls: dead whales and other large marine species sink to the seafloor, becoming long-term food sources for entire ecosystems
- Diurnal (daily) vertical migrations: food is more readily available in the shallower depths, so many deep sea species travel upwards at night to take advantage of the increased productivity. Some animals, like sharks, travel up along the seafloor, while invertebrates and planktonic fishes move directly upward in the water column.
Many deep-sea animals are scavengers or hunters, evolved to detect and consume scarce food in total darkness. Some species, once plankton feeders in shallow waters, have adapted into carnivores in the deep.
Other Ecosystems
Why the Deep Sea Matters?
Despite its inaccessibility, the deep-sea ecosystem plays a crucial role in regulating Earth’s climate, cycling nutrients, and supporting fisheries and biodiversity. Deep-sea sediments store carbon, helping to mitigate climate change. Currents influence global weather and nutrient flow.
Yet, deep-sea habitats are vulnerable to threats like deep-sea mining, overfishing, pollution, and climate change. With so much of this realm still undiscovered, protecting this delicate ecosystem before it’s exploited is essential for global ocean health.
