Sub-Zones of Pelagic Zone

The Pelagic zone can be divided into five sub-zones according to their depths. These are as follows:

Epipelagic Zone

The Epipelagic zone is the first layer of the Pelagic zone and can be characterized as follows:

• This uppermost layer extends from the ocean’s/lake’s surface to about 200m.
• The epipelagic zone is also called the sunlight of the surface zone, as it receives the most sunlight, allowing for photosynthesis and supporting a high concentration of phytoplankton.
• It is also home to most oceanic/pond/lake biodiversity, including plankton, surface plants, fish, sharks, dolphins, and marine birds.
• Epipelagic waters are generally warmer than deeper layers, and the wind actively mixes the water in these layers, keeping it warm.
• It is commercially the most important layer, harboring a significant portion of the Earth’s edible fish stocks.

Mesopelagic Zone

The features of the mesopelagic sub-zone can be summarized as follows:

• The zone of the oceanic water column between 200-1000 meters is known as the mesopelagic zone.
• It is also known as the Twilight Zone, as it receives reduced sunlight, creating a dimly lit environment.
• In adaptation to dimly-lit conditions, marine life usually consists of organisms with large eyes like Squids and Octopuses.
• As the mesopelagic zone receives little light photosynthesis is reduced, leading to a reliance on organic material falling from upper layers.
• There is a steep decrease in the temperature of water at the end of the epipelagic zone and in the mesopelagic zone called the thermocline.

Bathypelagic Zone

Bathypelagic sub-zone is the largest layer among the five subzones of the Pelagic Zone. It has the following characteristics:

• The pelagic zone between the depths of 1000-4000 meters is referred to as the Bathypelagic zone.
• As no sunlight reaches this zone, it results in a pitch-black environment and thus, this sub-zone is also called the midnight zone.
• To adapt to the darkness, many organisms exhibit bioluminescence as a form of communication, camouflage, or attracting prey.
• Species in these zones have also evolved to withstand extreme pressure conditions found at these depths, are mostly flattened, and have thick skin.
• Organisms in this zone often have slow metabolic rates to conserve energy, as lack of photosynthesis makes it a low-resource environment. It entirely depends on nutrients coming from the upper layers.

Abyssopelagic Zone

The abyssopelagic layer of the abyss is the dark, deep part of an ocean that is generally species-poor. The important features of this layer are:

• This is the layer of the pelagic zone that ranges from 4000-6000 meters deep.
• This layer is entirely dark and nutritionally poor.
• The abyssopelagic zone experiences intense water pressure due to its depth, with organisms adapted to withstand these conditions.
• Water temperatures in this region is consistently near freezing point.
• Very few organisms are found in these depths. Those that are found in this depth have unique adaptations, such as transparent bodies, bioluminescence, or elongated shapes, to thrive in this challenging environment.

Hadalpelagic Zone

The bottom layer of a deep ocean, which includes the water found in trenches and other sub-oceanic landforms, consists of this layer. It can be described as:

• This extends from below 6,000 metres to the ocean floor.
• Deep oceanic trenches, such as the Mariana Trench, and caves represent the deepest parts of the ocean.
• This layer experiences the highest water pressure and extremely low temperatures just above the freezing point of water.
• Due to the different landforms at the bottom, this zone has distinct geological formations.
• The Hadalpelagic Zone harbours limited but specialised extremophiles and adapted organisms, especially organisms that rely on chemosynthesis, which allows them to use chemical energy from the seafloor rather than photosynthesis, to produce food.

The pelagic zone is the open ocean’s water column, which extends from the surface to the bottom. Another name for it is the wide ocean. The phrase “open sea” (pélagos) in Ancient Greek is where the word “pelagic” originates. The five depth zones that make up the pelagic zone each have unique marine life and environmental characteristics.

The pelagic zone consists of pelagic zone animals and plants. In this article, we will study the definition of the pelagic zone, the different layers of the pelagic zone, the flora and fauna found in the pelagic zone, the human impact, and its conservation.