Introduction

Aquatic ecosystems are habitats in which living species interact. Marine organisms are living species with an aquatic environment for their food, habitats, reproduction, and other vital functions. They need water to survive.Water has characteristics that reflect the quality of the water body. An aquatic ecosystem’s physicochemical qualities dictate its functions and how long it can support living forms. Sediments in aquatic ecosystems provide substrate, nutrients, and a habitat for live aquatic resources in the same way that soil does in terrestrial environments. Sediments play a key role in environmental food cycles as well as the two water quality dynamics.

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 colonies of creatures that are reliant on one another and their surroundings. Marine ecosystems and freshwater ecosystems are the two main types of aquatic ecosystems. There are three types of freshwater ecosystems: lentic, lotic, and wetlands.

Freshwater Ecosystem

Freshwater is land-based water that is constantly cycling and has a low salt content Ex: Pond ecosystem. The study of freshwater and marine ecosystems is called Limnology.  Freshwater habitats cover 0.80% of the Earth’s surface area and contain 0.009% of the world’s total water. The net primary production is over 3%. They are home to 41% of the world’s recognized fish species.

Freshwater habitats are classified into three categories

• Lentic: Pools, ponds ecosystems, and lakes are examples of still or slow-moving water, and it is home to both floating and rooted plants, algae, and animals. Lentic ecosystems comprise all standing water environments, such as lakes and ponds. These ecosystems are home to algae, rooted and floating-leaved plants, and crustaceans such as crabs and shrimp. Here you’ll find frogs and salamanders, as well as reptiles like alligators and water snakes
• Lotic: rapidly moving water, for example, rivers and streams. They are home to a broad range of insects, including beetles, mayflies, and stoneflies. River dolphins, beavers, otters, eels, minnows, and trout are among the creatures that call it home
• Wetlands: The soil is inundated or saturated for at least a portion of the year. These are marshy areas that are frequently flooded and are home to a wide variety of plants and animals. Wetlands are home to water lilies, marshes, swamps, Northern Pikes, dragonflies, and Green Heron

Physical characteristics

• The concentration of dissolved salts in freshwater is minimal
• The temperature varies during the day and throughout the year. The surface temperature of tropical lakes is never below 40 °C in the case of freshwaters, it never goes above or below 40 °C, and in polar lakes, the temperature is never above 4 °C
• In temperate climates, the water surface layer freezes, but species live underneath the frozen surface
• Light has a great influence on freshwater ecosystems. Many suspended materials obstruct the penetration of light in water
• Certain animals float up to the water surface to take up oxygen for respiration. Depending on their size and habits, aquatic organisms may float in water, swim freely, or be sedentary (fixed)
• Photosynthesis is carried out by aquatic plants using carbon dioxide dissolved in water
• Depressions containing standing water are known as ponds and lakes. Lake Superior is the largest lake in the world in North America. Lake Baikal in Siberia is the deepest lake. Chilika Lake (Odisha) is the largest lake in India.

Marine Ecosystem

It includes oceans and seas, including organisms. The marine ecosystem occupies about 71 percent of the earth’s surface, with an average depth of around 4000 meters. Freshwater rivers gradually drain into the ocean, and various species live at various depths of the sea or ocean. The components of the marine ecosystem are:

1. Ocean Ecosystems: The Pacific Ocean is the largest ocean on Earth. The Atlantic Ocean is the second largest. The Indian Ocean is the third largest. The Arctic Ocean is the fourth largest. And the Southern Ocean is the fifth largest. Turtles, crabs, krill, shrimp, clams, oysters, octopus, jellyfish, snakes, eels, fish, whales, dolphins, turtles, crocodiles, sea urchins, starfish, coral, molluscs, sharks, rays, skates, squid, chimaera, lobsters, turtles, frogs, salamanders, lizards, geckos, snakes, eels and other creatures live in the ocean.
2. Estuaries:  Estuaries are places where salt water mixes with freshwater. This mixture causes salinity levels to rise. Saline water is less dense than freshwater. Therefore, estuaries are biologically productive because they trap plant nutrients. Examples of estuaries include – tidal marshes, river mouths, and coastal bays.
3. Coral Reefs: These are fondly referred to as the Rain Forest of Oceans, as they harbour a wide variety of aquatic flora and faunas. A coral reef is an aquatic ecosystem made up of corals. Coral polyps are held together by calcium carbonate in the formation of reefs. Stony corals, whose polypus clusters in groups, make up most of the coral reefs. The animal phylum Cnidaria includes sea anemones and jellies, and coral is part of Anthozoa. Unlike sea anemones, corals secrete a hard carbonate exoskeleton that supports and protects them. Warm, shallow, clear, sunny, agitated water is ideal for coral growth.
4. Coastal Ecosystem: Coastal ecosystems are unique in their structure, variety, and movement. Plant life dominates the bottom of the ecosystem. Fauna includes insects, snails, crabs, shrimp, and other species. Fish, lobsters, and shrimps live in these coastal areas.

Physical characteristics

• The open sea has a steady salinity of 3.6 percent
• The temperature range in the sea is much smaller than it is on land. In oceans, hydrostatic pressure increases with depth due to the water column
• Near the surface, it is 1 atm, and at the deepest point, it is 1000 atm
• Deeper-layer animals have adapted to high pressure
• Tides are a natural characteristic in marine environments due to the moon’s gravitational pull.

Conclusion 

In this article, we learned about various aquatic ecosystems. Freshwater and marine ecosystems are the two types of aquatic ecosystems.