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H1130 - Estuaries

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Estuaries are the downstream parts of a river valley, subject to the tide and extending from the limit of brackish waters. Contrary to the habitat type H1160 - Large shallow inlets and bays, there is a substantial freshwater influence. The mixing of freshwater and sea water results in a salt and fresh gradient. The farthest upstream influence of salt water forms the boundary of the estuary, the farthest influence of downstream fresh water forms the boundary of the marine system. An estuary forms an ecological unit with the surrounding terrestrial coastal habitat types (salt marshes and tidal marshes). These habitats, located at the boundary of the estuary, have been described as independent habitat types (H1310 - Salicornia and other annuals colonizing mud and sand, H1320 - Spartina swards and H1330 - Atlantic salt meadows) and are thus not considered under the type "estuary".
Estuaries contain a large variety of plants and animals thanks to the fresh and salt gradient and the mostly sheltered location. Estuaries contain more species than accompanying coastal areas, due to the environmental variation, the large amount of food and, a lower predation pressure for fish. Examples of species who are dependent on this brackish transitional environment are the worms Tubifex costatus_ and Paranais litoralis. #1.

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