The Open Ocean

The pelagic zone is the area of the ocean outside of coastal areas. This is also called the open ocean. The open ocean lies over and beyond the continental shelf. It's where you’ll find some of the biggest marine life species.

The sea floor (demersal zone) is not included in the pelagic zone.

The word pelagic comes from the Greek word pelagos meaning "sea" or "high sea". 

Different Zones Within the Pelagic Zone

The pelagic zone is separated into several subzones depending on water depth:

• Epipelagic zone (ocean surface to 200 meters deep). This is the zone in which photosynthesis can occur because light is available.
• Mesopelagic zone (200-1,000m) - This is also known as the twilight zone because light becomes limited. There is less oxygen available to organisms in this zone.
• Bathypelagic zone (1,000-4,000m) - This is a dark zone where water pressure is high and the water is cold (around 35-39 degrees). 
• Abyssopelagic zone (4,000-6,000m) - This is the zone past the continental slope - the deep water just over the ocean bottom. This is also known as the abyssal zone.
• Hadopelagic zone (deep ocean trenches, greater than 6,000m) - In some places, there are trenches that are deeper than the surrounding ocean floor. These areas are the hadopelagic zone. At a depth of over 36,000 feet, the Mariana Trench is the deepest known point in the ocean. 

Within these different zones, there can be a dramatic difference in available light, water pressure and the types of species you'll find there.

Marine Life Found in the Pelagic Zone

Thousands of species of all shapes and sizes live in the pelagic zone. You'll find animals that travel long distances and some that drift with the currents. There is a wide array of species here as this zone includes all of the ocean that is not either in a coastal area or the ocean bottom. Thus, the pelagic zone thus comprises the largest volume of ocean water in any marine habitat.

Life in this zone ranges from tiny plankton to the largest whales.

Plankton

Organisms include phytoplankton, which provides oxygen for us here on Earth and food for many animals. Zooplankton such as copepods are found there and also are an important part of the oceanic food web.

Invertebrates

Examples of invertebrates that live in the pelagic zone include jellyfish, squid, krill, and octopus.

Vertebrates

Many large ocean vertebrates live in or migrate through the pelagic zone. These include cetaceans, sea turtles and large fish such as ocean sunfish (which is shown in the image), bluefin tuna, swordfish, and sharks.

While they don't live in the water, seabirds such as petrels, shearwaters, and gannets can often be found above, on and diving under the water in search of prey.

Challenges of the Pelagic Zone

This can be a challenging environment where species are affected by wave and wind activity, pressure, water temperature and prey availability. Because the pelagic zone covers a large area, prey may be scattered over some distance, meaning animals have to travel far to find it and may not feed as often as an animal in a coral reef or tide pool habitat, where prey is denser.

Some pelagic zone animals (e.g., pelagic seabirds, whales, sea turtles) travel thousands of miles between breeding and feeding grounds. Along the way, they face changes in water temperatures, types of prey, and human activities such as shipping, fishing, and exploration.