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11.2.1. Aquatic ecosystems

Aquatic ecosystems

The main characteristics of aquatic ecosystems are:

Marine ecosystems (saltwater ecosystems)

The main characteristics of marine ecosystems are:

  • The average temperature of the great oceanic masses varies little, from 31 ºC on average in the equatorial zones, to -2 ºC in the polar zones.
  • Salinity is usually about 35 grams of salts per liter of water, an amount that remains fairly constant.
  • Marine currents, tides and waves condition the life of the marine ecosystem.
  • These ecosystems include the oceans, seas, marshes, etc., but can also appear salt water in the interior of the continents, such as the Dead Sea.

Some of the main saltwater ecosystems are:

  • Ecosystems on the cliffs. The waves hit the rocks and, together with the sea currents, make the organisms that are adapted to live there have to attach themselves strongly to the rocks, with sticky filaments like mussels or with suckers like limpets.
  • Ecosystems on the beaches  Live filter feeders, such as clams and other molluscs , which feed by filtering the water. There are also aquatic plants , such as Posidonia.
  • Ecosystems in the high seas. It is the largest zone, and animals are usually in the photic zone, the zone illuminated by the sun's rays. There is a lot of diversity of species : whales, dolphins, fish, etc.
  • Ecosystems in coral reefs. In shallow areas of tropical regions there may be coral reefs with great biodiversity, with spongespolypsfishcrustaceansmolluscs, etc.
  • Abyssal Plain Ecosystems. At the bottom of the sea, where sunlight does not reach, the animals have to adapt to total darkness. Some have organs that produce light.

Answer in your notebook

Why do you think there is more biodiversity in coastal areas than in very deep areas?

Freshwater ecosystems

The main characteristics of freshwater ecosystems  are:

Some of the main freshwater ecosystems are:

  • Ecosystems in rivers. In the upper reaches of the rivers, the water circulates at high speed along the steep slope. The organisms have to be strongly attached to the substrate or swim upstream. In the middle and lower reaches, the waters are calmer and there is a greater diversity of species, with many invertebrates and fish. In addition, the riparian forest is also home to numerous fauna and flora whose life depends on the river.
  • Ecosystems in wetlands. They are wetlands with stagnant waters, shallow, but with a great biodiversity  of birdsinvertebratesamphibians, etc.
  • Ecosystems in the lakes. Great diversity of species in these bodies of water that can be quite extensive and deep.

Brackish water ecosystems

The main characteristics of brackish water ecosystems are:

  • Brackish water is water that has more dissolved salts than  fresh water, but less than seawaterBrackish water is considered to be that which has between 0.5 and 30 grams of salt per liter of water (about 10 g/l on average). They are formed by the mixture of fresh water and salt water.
  • The vegetation and animals that live in these waters are adapted to this salinity.

Some of the main brackish water ecosystems are:

  • Ecosystems in the marshes. They are continental lands that are frequently flooded with seawater. The vegetation is herbaceous and there is a great diversity of migratory birds.
  • Ecosystems in estuaries. At the mouth of the rivers there can be mixtures of fresh and salt water, mainly due to the action of the tides . Species that tolerate a certain amount of salt usually live in these ecosystems .
  • Ecosystems in the deltas. They are formed by the accumulation of sediments at the mouth of some rivers in which there are not enough currents to transport said sediments. They have great biodiversity.
  • Ecosystems in the mangroves. They are tropical forests near the mouth of the rivers with trees that tolerate salt. They have a great biodiversity.

Answer in your notebook

Choose an aquatic ecosystem and explain what its biotope is like, its biocenosis, and some examples of the relationships that occur between the elements of the ecosystem.