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Definition of Euphotic Zone

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The layer which is closer to the surface of the earth is called the Euphotic Zone. This zone receives abundant light for the process of photosynthesis to take place.  Beneath this zone is the disphotic zone, which is poorly illuminated, and thus the rate of respiration exceeds those of the photosynthesis process.

The upper surface of the ocean which is of 200 meters (656 feet) is called the euphotic, also known as the "sunlight," zone. In this zone particularly the majority of the fisheries activities are done and it is home to many protected marine mammals.


Definition of Photic Zone

In this zone, which is called the photic zone, here the photosynthesis rate exceeds the respiration rate. This occurs because of the abundant availability of solar energy, which acts as a great energy source for the process of photosynthesis. This process helps mainly the primary producers like the phytoplankton. 

Phytoplankton grows extremely quickly as the sunlight's heavy influence enables the plant process to be at a fast rate. For the fact, even ninety-five percent of the photosynthesis occurs in the photic zone in the ocean. Hence, if we go deeper, beyond the photic zone, which is called the compensation point there live negligible phytoplankton due to insufficient sunlight. 


About Eutrophic Zone

The euphotic zone is described as the layer which is closer to the surface, this receives quite enough amount of light for the process of photosynthesis to occur. Under this zone lies the disphotic zone, which is not illuminated properly and hence the rates of respiration exceed those of photosynthesis. 

The real depth of these zones depends on the local conditions like cloud cover, water turbidity, or the ocean surface. Generally, the euphotic zone extends to a depth of about 80 to 100 meters while the disphotic zone measures in depths of about 80 to 700 meters. All kinds of marine organisms are found abundantly in the photic zone, mainly in the euphotic portion. Another fact of these organisms is that they inhabit in the aphotic zone, while they migrate vertically in the photic zone in the night time. Other organisms like the tripod fish and other species stay in darkness all their lives.


Euphotic Zone Organisms

Euphotic zone organisms mainly include most of the ocean fishes like sharks and rays, man o war, jelly fishes, sea turtles, corals, seals and zooplankton. 

Some of these animals in this zone adapt to the technique of countershading. Countershading is done when an animal is light on its underside while dark on its upper parts. In this case, when a predator looks down at this animal it mixes with the darker waters and when a predator looks at this animal from below, the light under their belly disappears into the lighted area. This countershading adaptation helps camouflage the organism; they hide from their predators. Sharks use this adaptability the most. 


Aphotic and Photic Zone

The ocean with the largest aquatic biome can be categorized into these different zones. The Photic zone and the Aphotic zone are two oceanic zones that can be classified vertically based on the amount of sunlight that can be penetrated. The Photic zone receives the sunlight that penetrates in the photic zone, this enables the process of photosynthesis. Here the diversity of organisms is quite high in the photic zone as here in this zone life is more favourable for animal life.

Whereas, the aphotic zone is that portion of ocean that does not receive any sunlight. In this zone, sunlight does not penetrate. All the photosynthetic organisms die in this zone for the lack of sunlight. The diversity of organisms is quite low here and a few organisms live in this aphotic zone.


Euphotic Zone Plants

A huge variety of oceanic vegetation and its types and all other types of plants can grow in this sunlit area. Plants include marine algae, plankton and surprisingly, even the mangroves can grow here. The plants modified themselves to allow them to float in the ocean. In addition to this, these plants have a special ability to carry out the process of photosynthesis and in turn, serves as a diet for the other marine animals.

FAQs (Frequently Asked Questions)

1. What is Phytoplankton?

Ans.  Phytoplanktons are marine algae that are microscopic in size. They are also known as microalgae, which is quite similar to terrestrial plants. Here they contain chlorophyll and they require sunlight to help support them live and grow. Most of the phytoplankton are buoyant and they float in the upper part of the ocean, where they can find sunlight and where the sunlight penetrates the water, in the euphotic region.


Plankton majorly includes plants and animals which can float along with the sea's tides and ocean currents. Their name means drifter or wanderer in Greek terminology. There are two types of plankton – the tiny plants which are known as phytoplankton, and others are the weak-swimming animals known as the zooplankton.

2. What Do You Mean By Photosynthesis Rate?

Ans. Photosynthetic rate means the capacity which is a measure of the maximum rate which indicates how it leaves and can fix the carbon during the process of photosynthesis. This is typically measured as the amount of carbon dioxide which is fixed per meter squared as per second.


The rate of photosynthesis can be defined as the terms of the rate of oxygen that is the production either per unit mass (or an area) of the green plant tissues or measured as per unit weight of the total chlorophyll.

3. Who are Primary Producers?

Ans. Green plants and certain types of bacteria are able to convert the inorganic matter into biomass by using energy from solar radiation or by chemical energy. The primary producers are the first to come in connection with the food chain and thus they are called the primary producers, known as autotrophs.


Two major types of primary producers are phototrophs and chemotrophs. Phototrophs are those who use the energy from the sun, to convert carbon dioxide into carbohydrates. This process is called photosynthesis.

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