Aquatic Ecosystem

An Aquatic ecosystem is a habitat comprising of living beings residing within a water body. This water body can include marine and fresh water bodies. The aquatic system consists more than 70% of the earth. Aquatic ecosystems are systems composed of living organisms and non-living elements interacting in a watery environment. An aquatic ecosystem is a community of plants and animals that primarily depend on water.

Types of Aquatic ecosystems

Marine Ecosystems
Freshwater Ecosystems

Marine Ecosystem

Marine ecosystems cover approximately 71% of the Earth's surface and contain approximately 97% of the planet's water. They generate 32% of the world's net primary production. They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts, in the water. Approximately 85% of the dissolved materials in seawater are sodium and chlorine. Seawater has an average salinity of 35 parts per thousand (ppt) of water. Salinity varies among different marine ecosystems.
Different habitats ranging from coral reefs to estuaries make up this largest aquatic ecosystem in the planet. Classes of organisms found in marine ecosystems include brown algae, dinoflagellates, corals, cephalopods, echinoderms, and sharks.

Main examples of marine ecosystems include:

Ocean: Main body of salty water that is further divided into important oceans and smaller seas. Major oceans include the Pacific Ocean, Indian Ocean, Arctic Ocean, Atlantic Ocean and Southern Ocean.
Intertidal zone: Area which remains underwater at high tide and remains terrestrial at low tide. Different types of habitats including wetlands, rocky cliffs and sandy beaches fall under intertidal zones.
Estuaries: Areas between river and ocean environment that are prone to tides and inflow of both freshwater and saline water. Due to this inflow, estuaries have high levels of nutrients. There are different names of estuaries such as inlets, lagoons, harbours etc.
Coral Reefs : Often referred as the “rainforests of the sea", coral reefs are mounds found in marine waters as a result of accumulation of calcium carbonate deposited by marine organisms like corals and shellfish. Coral reefs form the most varied marine ecosystems in the planet, but cover less than one percent of the world’s ocean. Nevertheless, around 25 percent of marine animals including different types of fishes, sponges and mollusks are found in coral reefs.

Freshwater Ecosystem

Freshwater ecosystems cover 0.80% of the Earth's surface and inhabit 0.009% of its total water. They generate nearly 3% of its net primary production. Freshwater ecosystems contain 41% of the world's known fish species. The water in freshwater ecosystems is non-saline which means water has no salt content. It includes Standing Water like lakes and ponds and Moving Water like rivers and streams.

Freshwater ecosystem is further divided into three basic types of freshwater ecosystems:

Lentic: slow moving water, including pools, ponds, and lakes.
Lotic:faster moving water, for example streams and rivers.
Wetlands:areas where the soil is saturated or inundated for at least part of the time.

Lotic ecosystems refer to systems with rapid flowing waters that move in a unidirectional way. Best examples are rivers and streams, which harbour several species of insects and fishes. Crayfish, crabs, clams and limpets are commonly found in streams and rivers. Various mammals such as beavers, otters and river dolphins also inhabit lotic ecosystems.
Lentic Ecosystem are still waters such as lakes and ponds that have a community of biotic and abiotic interactions. Ponds and lakes have a diverse variety of organisms including algae, rooted and floating-leaved plants, invertebrates such as crabs, shrimps, crayfish, clams etc, amphibians such as frogs and salamanders; and reptiles like alligators and water snakes.
Wetlands: The best examples of wetlands include swamps and marshes, where the water is completely or partially shallow. Biologically, wetlands are known to be too diverse as it harbours numerous animals and plant species. Plants such as black spruce, water lilies, mangrove, tamarack and sedges are commonly found in wetlands. Various species of reptiles and amphibians are also found in wetlands.

Apart from this wide variety of natural aquatic ecosystems, humans continue to build and develop a large number of artificial aquatic ecosystems. These range from reservoirs, canals, channels for irrigation and drainage, and paddy fields for the production of rice, through lakes and ponds built for landscaping and fish culture, down to the decorative home aquarium. Human populations have always lived close to water. The ecosystems on seacoasts, by lakes, and in the river valleys are under tremendous pressure from urbanization, industrialization, and commerce.