Aquatic ecosystems

Aquatic Ecosystems are complex environments that play a crucial role in the Earth's hydrological cycle and are home to a diverse array of species. They can be broadly classified into two types: marine ecosystems and freshwater ecosystems.

Marine Ecosystems

Marine ecosystems cover approximately 71% of the Earth's surface and contain more than 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. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the sea where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides; in this figure it is termed the littoral zone.

Freshwater Ecosystems

Freshwater ecosystems cover 0.78% 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. These ecosystems are divided into lentic ecosystems (slow moving water, including pools, ponds, and lakes), lotic ecosystems (faster moving water, for example streams and rivers), and wetlands.

Importance of Aquatic Ecosystems

Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife. Aquatic ecosystems are also used for human recreation, and are very important to the tourism industry, especially in coastal regions.

Threats to Aquatic Ecosystems

The health of an aquatic ecosystem is degraded when the ecosystem's ability to absorb a stress has been exceeded. A stress on an aquatic ecosystem can be a result of physical, chemical or biological alterations of the environment. Physical alterations include changes in water temperature, water flow and light availability. Chemical alterations include changes in the loading rates of biostimulatory nutrients, oxygen consuming materials, and toxins. Biological alterations include over-harvesting of commercial species and the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems. There are many examples of excessive stresses with negative impacts.

See Also

• Marine biology
• Freshwater biology
• Ecology
• Ecosystem

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