Distinguish Between Biota of the Pelagic and Benthic zones of the Oceans

What is Benthic 

Benthic means living or occurring at the bottom of the water body. The benthic zone includes the water layer present just above the bottom. Hence, the water in the benthic zone always contacts the bottom of the lake or ocean. The location of the benthic zone depends on the depth of the water body. In the deep ocean, sunlight may not reach the benthic zone, leaving it darker. Therefore, the temperature of the benthic zone is also low. Also, due to the weight of the large volume of water above, the benthic zone has to withstand great pressure.

The organisms that live at the bottom are called benthos. Benthos are adapted to different features in the benthic zone including low light and temperature as well as high pressure. Due to the lack of sunlight, photosynthetic organisms cannot survive in the benthic zone. Therefore, benthos depend on the organic matter drifted down from the above water layers. Mainly scavengers and detrivores live in the benthic zone. Benthos includes sea stars, oysters, clams, snails, crustaceans, cephalopods, sea cucumbers, brittle stars, and sea anemones. Most benthic organisms serve as a food source for fish.

What is Pelagic

Pelagic means occurring or living in the open area of the water body. The pelagic zones include the topmost layers of the water body, which perform important ecological functions such as heat absorption, oxygen absorption, and food production through photosynthesis. As the availability of sunlight, oxygen, and temperature decrease and the pressure increases with the increasing depth of the water body, the pelagic zone can be subdivided based on the fluctuation of the factors.

Main Difference - Benthic and Pelagic

The pelagic zone is rich in resources to sustain life; hence, most of the ocean life, both flora, and fauna is found in this zone. Photosynthetic organisms from the microscopic level (diatoms, plankton, microalgae) to the macroscopic level (large algae and seaweed) occur in this zone. Also, due to the availability of plants, herbivores, as well as carnivores, are active in the pelagic zone.

Following are the differences between the Benthic and Pelagic zone:

• Benthic zone is the layer closer to the bottom of a water body, whereas the pelagic zone refers to the uppermost layers of a water body.

• Organisms that live in the benthic region are coined as ’benthos’, and organisms found in the pelagic zones are referred to as pelagic organisms.

• Referring to the open sea, the benthic zone is characterized by low temperatures, low dissolved oxygen levels, low/no light, and high pressures. However, there is a gradient of these in the pelagic zone from top to bottom.

• If we compare the diversity in these zones, resource-rich pelagic waters harbor higher diversity than the benthic zone that has lower resources.

• Photosynthesis does take place in the epipelagic zone, but the benthic zone does not get enough light for this.

• Pelagic food webs are powered by photosynthesis whereas benthic communities are normally powered by detritus drifted from the upper layers.

• No photosynthetic organism can be found in the benthic region; it is dominated by detritivores and scavengers. In the pelagic zone, photosynthetic organisms, as well as active predators, are dominant.

• All most all the creatures in the benthic zone are bottom-dwellers or sessile animals whereas all the creatures in the pelagic zone are free-living.

Example: Benthic- crabs, fishes, prawns, and lobsters; Pelagic- mackerel, sardine, tuna

Similarities Between Benthic and Pelagic

  • Benthic and pelagic are two types of organisms classified based on the zone of the water body they live.
  • Each type of organism is adapted to the environment they live.

Difference Between Benthic and Pelagic


Benthic means relating to, or occurring at the bottom of a body of water while pelagic means relating to, or living or occurring in the open sea. This is the basic difference between benthic and pelagic. Based on this basic difference between benthic and pelagic, the features of these two zones to vary.

Light and Temperature

Benthic zones are darker and colder while pelagic zones are lighter and warmer.


Benthic zones have a poor oxygen content while pelagic zones have a good oxygen content.


Benthic zones encounter tremendous pressure while the pressure of the pelagic zone is not more than atmospheric pressure.

Nourishment and Resources

Benthic zones are rich in nutrients and resources while pelagic zones are poor in nutrients and resources.

Because of the above featural difference between benthic and pelagic zones, the features of the organisms that make these two zones as their habitat to vary.

Types of Organisms

Benthos are mainly scavengers and detritivores while pelagic organisms are mainly plants, herbivores, and carnivores.

Food Sources

Benthos depend on decaying organic matter while pelagic organisms depend on plants.


Benthic refers to occurring or living in the bottom of the water body or the benthic zone, which is darker, colder, and pressurized. But, pelagic refers to living in the topmost regions of the water body or the pelagic zone, which is lighter and warmer. Scavengers and detrivores live in the benthic zone while plants, herbivores, and carnivores live in the pelagic zone. The main difference between benthic and pelagic is the features of the zone and the type of organisms that live.

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