In contrast to land-based terrestrial ecosystems, an aquatic ecosystem is one that exists in and around a body of water. Aquatic ecosystems are made up of communities of organisms that are reliant on one another and their surroundings. This article will explain to you about Aquatic Ecosystem which will be helpful in preparing the Environment syllabus for the UPSC Civil service exam.

Aquatic Ecosystem

Aquatic Ecosystem - Concept

• An aquatic ecosystem is one that is based on water.
• The word 'aquatic' is derived from the Latin word 'aqua', which means water.
• So, in a water-based setting, an aquatic ecosystem is a community of species that live together, interact, and to some extent rely on one another.
• Aquatic ecosystems are divided into the following subcategories based on the concentration of salt content.
  • Freshwater ecosystems: Rivers, lakes and ponds.
  • Brackish Water Ecosystems: Mangroves, Estuaries, etc.
  • Marine ecosystems: Oceans, Seas, etc.

Zones of Aquatic Ecosystem

Freshwater Ecosystems

• Freshwater ecosystems are made up of water on land that is constantly cycling and has a low salt content (always less than 5 ppt).
• Freshwater ecosystems are divided into two categories:

Lentic Ecosystem

• They include all ecosystems with static or still water.
• Lakes and ponds are among the most common examples of the Lentic Ecosystem.
• Algae, crabs, shrimp, and amphibians like frogs and salamanders also live in these habitats.
• It is also called the lacustrine ecosystem or the still water ecosystem.

Lotic Ecosystem

• These primarily relate to fast-moving water bodies that run in one direction, such as rivers and streams.
• Furthermore, these settings support a diverse range of organisms, including beetles, mayflies, stoneflies, and a variety of fish species, including trout, eel, and minnow.
• It is also called the riverine ecosystem.

Marine Ecosystems

• Marine ecosystems are defined as bodies of water with a salt concentration equal to or greater than that of seawater (i.e., 35 ppt or above).
• Marine ecosystems are the largest of the Earth's aquatic ecosystems, and they exist in salty waters.
• As said earlier, freshwater ecosystems have a lower salt content than saltwater ecosystems.

Brackish Water Ecosystems

• When freshwater joins seawater, brackish water is found.
• Brackish water ecosystems have a salt level of 5 to 35 parts per million.
• Estuaries, salt marshes, mangrove swamps, and forests are just a few examples.
• The River Thames, which runs through London, is an example of a traditional river estuary.

Aquatic Organisms

• The aquatic organisms are categorized according to their occurrence zones.
• Neuston: These species, such as floating plants, live at the air-water interface.
• Periphyton: Organisms that attach to the stems and leaves of rooted plants or substances that emerge above the mud's surface, such as sessile algae are called periphyton.
• Plankton: Plankton refers to microscopic floating organisms such as algae, diatoms, protozoans, and larvae.
• Both microscopic plants like algae (phytoplankton) and animals like crustaceans and protozoans are included in this category (zooplankton).
• Since planktons' locomotory strength is limited, their dispersion is mostly governed by currents in aquatic habitats.
• Nekton: This group consists of strong swimmers who can swim against the currents.
• Benthic: These species live at the bottom of a water mass and are known as benthic organisms.

Factors Limiting the Productivity of Aquatic Habitats

• The most important limiting variables in aquatic environments are sunlight and oxygen.

Sunlight

• As sunlight moves through the water column, its penetration decreases fast.
• The extent of plant dispersal is determined by the depth to which light penetrates a lake.
• The water becomes murky due to suspended particulate matter such as clay, silt, phytoplankton, and so on.
• Turbidity significantly reduces the amount of light that can penetrate and the amount of photosynthetic activity that can occur.
• They are divided into photic and aphotic zones based on light penetration and plant distribution.

Photic Zone

• The photic (or "euphotic") zone is defined as the area between the lake's surface and a light level that is 1% of that at the surface.
• The transparency of the water determines the depth of this zone.
• The photic zone is where photosynthetic action takes place.
• Both photosynthesis and respiration occur.

Aphotic Zone

• The aphotic zone is formed by the bottom layers of aquatic environments, where light penetration and plant growth are restricted (profundal zone). This zone is occupied solely by respiratory activities.
• The aphotic zone spans from the end of the photic zones to the bottom of the lake.

Dissolved Oxygen

• The average dissolved oxygen concentration in freshwater is 10 parts per million by weight.
• This is 150 times lower than the oxygen concentration in the same amount of air.
• Through the air-water contact and the photosynthetic activity of aquatic plants, oxygen enters the aquatic ecosystem.
• Through the air-water interface and organism respiration, dissolved oxygen departs the water body (fish, decomposers, zooplankton, etc.).
• Many aquatic creatures die when the dissolved oxygen content goes below 3-5 ppm.

Winterkill A layer of ice on the surface of a body of water can effectively block light. In such a water body, photosynthesis ceases while respiration continues. If the water body is shallow, the fish will die due to a lack of oxygen. Winterkill is the term for this condition. Fish Winterkill

Temperature

• Aquatic creatures have a narrow temperature tolerance limit because water temperatures are less susceptible to change.
• As a result, as compared to variations in air temperatures in terrestrial creatures, even minor changes in water temperature pose a significant hazard to aquatic organisms' existence.

Significance of Aquatic Ecosystems

• The health of aquatic ecosystems is critical to the planet's overall health.
• Our planet isn't named the blue planet for nothing: the seas, with their fish, weeds, invertebrates, and mammals, as well as the rivers, lakes, streams, marshes, and ponds of the world, are all valuable biodiversity reservoirs.
• The seas also play a role in regulating global temperature and locking carbon out of the atmosphere.
• Though we should all attempt to reduce our consumption of fish, there is no denying that fish and other aquatic species are essential food sources for many terrestrial animals (i.e. animals that live on land).
• Aquatic ecosystems recycle nutrients, purify water, reduce flooding, increase and maintain streamflow, replenish groundwater, and provide wildlife habitat and recreational opportunities.
• They provide a number of functions for human populations, including water for drinking and irrigation, recreational activities, and habitat for economically important fisheries, in addition to contributing to biodiversity and ecological production.

Conclusion

There are many different types of aquatic habitats around the world, each of which is home to some incredible animals. As our marine ecosystems are so vast and mysterious, scientists believe they have only documented around 10% of the organisms that reside there. However, pollution, carbon emissions, and overfishing pose severe threats to these aquatic ecosystems. The Great Barrier Reef, one of the world's natural beauties, is already withering in front of our eyes. It is critical that we all act today to protect the aquatic ecosystems of the world for future generations. We can achieve this by lowering our emissions, eliminating the use of toxic chemicals that can seep into the oceans and rivers, and removing fish from the food chain.

GS Mains Questions and Model Answers

Q1: Discuss the significance of aquatic ecosystems in maintaining ecological balance.

Answer: Aquatic ecosystems are crucial for maintaining ecological balance as they provide essential services that support both biodiversity and human well-being. These ecosystems act as natural filters, purifying water and regulating nutrient cycles. They support diverse communities of organisms, including phytoplankton, zooplankton, fish, and invertebrates, which form intricate food webs. The health of aquatic ecosystems directly influences the global climate, as they play a significant role in carbon sequestration. Furthermore, they provide resources such as food, recreation, and medicinal compounds. Their ability to support diverse life forms contributes to the resilience of our planet, underscoring the importance of protecting these ecosystems from threats like pollution, habitat loss, and climate change. Effective management and conservation strategies are essential to ensure that aquatic ecosystems continue to thrive and provide vital services to the environment and society.

Q2: Analyze the threats facing aquatic ecosystems and suggest measures to mitigate these threats.

Answer: Aquatic ecosystems face numerous threats, including pollution, overfishing, climate change, and habitat destruction. Pollution from agricultural runoff, industrial discharges, and plastic waste can severely degrade water quality, impacting the health of aquatic life. Overfishing disrupts the balance of food webs and threatens species' survival, while climate change alters water temperatures and hydrological cycles, further stressing these ecosystems. To mitigate these threats, comprehensive strategies must be implemented. These include enforcing stricter pollution controls, promoting sustainable fishing practices, and restoring natural habitats. Moreover, raising public awareness about the importance of aquatic ecosystems and their conservation is vital. Policies encouraging the use of biodegradable materials and reducing plastic consumption can significantly diminish pollution levels. Collaborative efforts involving government, local communities, and conservation organizations can create effective frameworks to protect aquatic ecosystems, ensuring their sustainability for future generations.

Q3: Evaluate the role of aquatic ecosystems in supporting economic activities.

Answer: Aquatic ecosystems play a significant role in supporting various economic activities that are vital for the livelihoods of millions globally. These ecosystems provide essential resources such as fish and shellfish, which are crucial for the fishing industry, contributing to food security and employment. Additionally, aquatic environments support aquaculture, allowing for sustainable fish farming practices that meet the growing demand for seafood. Tourism and recreation are also significantly influenced by healthy aquatic ecosystems, attracting visitors for activities such as fishing, boating, and wildlife observation. Furthermore, these ecosystems offer services like water purification and flood control, which reduce economic losses from environmental degradation. However, to maintain these economic benefits, it is essential to adopt sustainable practices and implement conservation strategies that protect aquatic ecosystems from overexploitation and pollution. By prioritizing the health of these ecosystems, we can ensure that they continue to provide valuable resources and services that underpin economic stability and growth.

Previous Year Questions on  Aquatic ecosystem

1. UPSC CSE Prelims 2020

Question: Which of the following is NOT a component of an aquatic ecosystem?

a) Phytoplankton

b) Zooplankton

c) Biomes

d) Benthos

Answer: c) Biomes

Explanation: Biomes are large ecological areas on the earth's surface, whereas phytoplankton, zooplankton, and benthos are specific components of aquatic ecosystems.

2. UPSC CSE Mains 2019

Question: Explain how human activities impact aquatic ecosystems and suggest measures to protect these ecosystems. (200 words)

Answer: Human activities significantly impact aquatic ecosystems through pollution, habitat destruction, and overfishing. Pollution from agricultural runoff introduces excess nutrients and toxins into water bodies, leading to problems such as eutrophication and biodiversity loss. Habitat destruction, caused by urban development and dam construction, disrupts the natural flow of rivers and the integrity of wetlands. Overfishing depletes fish populations, undermining the balance of aquatic food webs and threatening species extinction. To protect these ecosystems, it is essential to implement sustainable practices. This includes establishing marine protected areas, enforcing fishing quotas, and promoting best management practices in agriculture to reduce runoff. Restoration projects, such as wetland rehabilitation and riverbank restoration, can help recover degraded habitats. Additionally, public education and community engagement in conservation efforts can foster a culture of respect for aquatic environments. By addressing these human-induced threats, we can enhance the resilience and health of aquatic ecosystems, ensuring they continue to thrive and provide vital services.