Pelagic Zone

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Pelagic Zone Definition

“Pelagic zone is the region of the ocean outside the coastal areas and is also known as the open ocean.”

What is Pelagic Zone?

The pelagic zone is that region of lake, river or ocean that is not associated with the shore or the bottom. The pelagic zone organisms inhabiting the zone do not come in contact with the bottom or the shore throughout their lives. The pelagic zone is nutrient-poor. The large fish find their food by swimming long distances or drifting with currents and feeding on nutrient-deficient organisms.

Sub-Zones of Pelagic Zone

The pelagic zone is further divided into the following sub-zones based on the penetration of light.

Epipelagic Zone

  • This zone stretches from the surface to a depth of about 200 metres.

  • It is the surface zone where sufficient light penetrates for photosynthesis.

  • This region is dominated by phytoplankton, diatoms, and dinoflagellates.

  • Large fishes such as tunas and sharks are found in this zone. That is why the smaller animals come up to this zone only at night to stay away from the large predators around.

Mesopelagic Zone

  • This zone extends from 200-1,000 metres below the epipelagic zone.

  • This is known as the twilight zone.

  • Although some light reaches the region, it is not sufficient for photosynthesis.

  • Some animals found in this zone have large eyes to make the best use of limited light.

  • The oxygen concentration is also very low here.

  • The organisms such as squids, nautilus shells, swordfish, etc. have the capacity to survive in low oxygen concentrations.

Also read: Ecosystem

Bathypelagic Zone

  • This is known as the dark zone where no light can reach.

  • This zone extends from 1,000-4,000 metres below the continental slope.

  • This is the zone of high pressure. The organisms with special features to withstand such high pressures can survive in this zone. E.g., the fishes found here lack a swimbladder.

  • The organisms here stay still to conserve energy.

  • The fishes exhibiting bioluminescence are prominent in this zone.

  • The temperature here stays between 2-4℃.

  • Giant squids and sperm whales are found in this zone.

Abyssopelagic Zone

  • This zone extends from 4,000- 6,000 metres and is the region where the continental slope levels off.

  • It comprises more than 30% of the bottom ocean.

  • The organisms here are colourless and blind.

Hadopelagic Zone

  • This zone extends from 6,000-11,000 metres.

  • Very few species are observed in this zone.

  • Food availability is very low here.

  • Many organisms found here live in hydrothermal vents.

The epipelagic and mesopelagic zones are the photic zones, while all the other zones are the aphotic zones with no light penetration.

Also Read: Benthic Zone

Pelagic Zone Animals

The organisms in the pelagic zone range from tiny planktons to large mammals like whales. Phytoplanktons provide oxygen for humans and food for many animals.

Zooplanktons are also found in this zone. These are heterotrophic planktons that include most of the micro and macroorganisms.

Invertebrates like jellyfish, squids, octopus and krill are also found in the pelagic zone.

Large ocean vertebrates such as crustaceans, sharks, bluefin tuna, and sea turtles live or migrate through the pelagic zone. Seabirds such as shearwaters, petrels and gannets can be found above the pelagic zone.

Challenges in the Pelagic Zone

The species in this zone might be affected by the wave and wind activity, pressure, availability of prey, and temperature of the water. The pelagic zone is spread over a wide area. The prey might be scattered over some distance and the animals might have to travel very far in search of it.

Some animals have to travel miles between the breeding and feeding grounds. They encounter changes in the water temperature, human activities and types of prey. Thus, the animals in the pelagic zone face a few challenges.

Also read: Aquatic Ecosystem

For more information on Pelagic Zone and related topics, keep visiting BYJU’S Biology website or go to BYJU’S app for further reference.

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