Estuaries

Adaptations to Life in the Estuary

mangrove trees | blue crabs

Pickleweed (Salicornia sp.) is an edible halophylic (salt-loving) plant that tolerates the unique and constantly changing environment of the salt-marsh estuary. Click on image for more details and a larger view.

Mangrove trees and blue crabs are some of the estuarine species that have adapted to unique environmental conditions. In almost all estuaries the salinity of the water changes constantly over the tidal cycle. To survive in these conditions, plants and animals living in estuaries must be able to respond quickly to drastic changes in salinity.

Plants and animals that can tolerate only slight changes in salinity are called stenohaline (Sumich, 1996). These organisms usually live in either freshwater or saltwater environments. Most stenohaline organisms cannot tolerate the rapid changes in salinity that occur during each tidal cycle in an estuary.

Plants and animals that can tolerate a wide range of salinities are called euryhaline. These are the plants and animals most often found in the brackish waters of estuaries. There are far fewer euryhaline than stenohaline organisms because it requires a lot of energy to adapt to constantly changing salinities. Organisms that can do this are rare and special. Some organisms have evolved special physical structures to cope with changing salinity. The smooth cordgrass (Spartina alterniflora) found in salt marshes, for example, has special filters on its roots to remove salts from the water it absorbs. This plant also expels excess salt through its leaves.

Oysters can live in the brackish waters of estuaries by adapting their behavior to the constantly changing environment. Click on image for more details and a larger view. (Photo: Apalachicola NERRS site)

Unlike plants, which typically live their whole lives rooted to one spot, many animals that live in estuaries must change their behavior according to the surrounding waters' salinity in order to survive. Oysters and blue crabs are good examples of animals that do this.

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