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 on Euphotic Zone
1. What is the euphotic zone in geography?
The euphotic zone, also known as the sunlight or photic zone, is the uppermost layer of a body of water (like an ocean or lake) that receives enough sunlight for photosynthesis to occur. The name comes from the Greek 'eu' meaning 'well' and 'photos' meaning 'light'. This is where the vast majority of marine life and primary productivity is concentrated.
2. What is the typical depth of the euphotic zone?
The depth of the euphotic zone can vary significantly, but it typically extends from the surface down to about 200 metres (660 feet) in clear, open ocean waters. In coastal or murky waters with high turbidity, its depth can be much shallower, sometimes only a few metres.
3. What kinds of animals and plants live in the euphotic zone?
The euphotic zone is teeming with life. Its base is formed by phytoplankton (microscopic plants) which perform photosynthesis. These primary producers support a vast food web that includes:
- Zooplankton: Microscopic animals that feed on phytoplankton.
- Fish: A wide variety of species, from small fish like sardines to large predators like tuna and sharks.
- Marine Mammals: Whales, dolphins, and seals that come to the surface to breathe and feed.
- Sea Turtles and Jellyfish: Other common inhabitants of this sunlit layer.
4. What is the main difference between the euphotic zone and the photic zone?
While often used interchangeably, there is a technical difference. The photic zone refers to any depth where any amount of sunlight penetrates. The euphotic zone is a more specific sub-layer within the photic zone where the light is intense enough for the rate of photosynthesis to be greater than the rate of respiration. Essentially, it's the zone where net primary production can happen.
5. Why is the euphotic zone considered the most important oceanic zone for life on Earth?
The euphotic zone is fundamentally important because it is the location of nearly all oceanic primary productivity. Phytoplankton in this zone generate a massive amount of organic carbon through photosynthesis, forming the base of the entire marine food web. Furthermore, this process releases a significant portion of the Earth's oxygen, making it crucial for the planet's atmosphere.
6. What factors can change the depth of the euphotic zone?
The depth of the euphotic zone is not constant and is influenced by several factors, including:
- Water Turbidity: Suspended sediments, pollutants, or dense blooms of phytoplankton can block sunlight and make the zone shallower.
- Season and Latitude: The angle of the sun changes with seasons and latitude, affecting how deeply light penetrates the water. The zone is deeper in the tropics and shallower at the poles.
- Weather Conditions: Cloud cover can temporarily reduce the amount of light reaching the water's surface.
7. How do the euphotic, disphotic, and aphotic zones of the ocean compare?
These three zones are defined by the amount of sunlight they receive.
- The Euphotic Zone ('well-lit'): From the surface to about 200m, it has enough light for photosynthesis and supports most marine life.
- The Disphotic Zone ('poorly-lit'): From about 200m to 1,000m, it receives some sunlight, but not enough for photosynthesis. It is often called the twilight zone.
- The Aphotic Zone ('no light'): Below 1,000m, it is in complete darkness. Life here relies on consuming organic matter that drifts down from above or on chemosynthesis near hydrothermal vents.
