Difference Between Benthic and Pelagic

The main difference between benthic and pelagic is that the benthic means relating to/occurring at the bottom of a body of water while pelagic means relating to/living or occurring in the open sea. Furthermore, benthic regions can be colder and darker while pelagic regions are lighter and warmer.

Benthic and pelagic are two types of aquatic living forms classified based on the zone in which they live.

Key Areas Covered

1. What is Benthic
     – Definition, Features, Types of Organisms Found
2. What is Pelagic
     – Definition, Features, Types of Organisms Found
3. What are the Similarities Between Benthic and Pelagic
     – Outline of Common Features
4. What is the Difference Between Benthic and Pelagic
     – Comparison of Key Differences

Key Terms

Benthic, Benthos, Light, Pelagic, Pressure, Temperatures

What is Benthic

Benthic means living or occuring 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 a great pressure.

Figure 1: Distribution of Organisms in Benthic and Pelagic Zone

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 to 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.

Figure 2: Pelagic Zones

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 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.

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 organisms is adapted to the environment they live.

Difference Between Benthic and Pelagic

Definition

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 too vary.

Light and Temperature

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

Oxygen

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

Pressure

Benthic zones encounter a 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 too 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.

Conclusion

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 live.

Reference:

1. “Understanding the Differences Between Benthic and Pelagic Zones.” ScienceStruck, ScienceStruck, 5 Mar. 2018, Available Here

Image Courtesy:

1. “Scheme eutrophication-en” By © Hans Hillewaert / (Public Domain) via Commons Wikimedia 
2. “Pelagiczone” (Public Domain) via Commons Wikimedia