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Estuary

Characterized by the mixing of freshwater streams with ocean tides
Great blue herons are only one of the animals that benefits from a healthy Willapa Bay Estuary/Photo Courtesy of Curt Stephens

Willapa Bay is a major estuary on the Pacific Coast and at mean high tide encompasses approximately 70,400 acres (28,500 hectares). An estuary is defined as the area near the mouth of a river, or rivers, in the case of Willapa Bay, where oceanic tidal waters and freshwater currents collide and mix. Biologically, estuaries are among the most productive environments on earth and provide important habitat for a large variety of organisms. This high productivity is due basically to physical and biological processes unique to estuaries. Dissolved organic nutrients from detrital (dead plants and animals, and excrement) material enter the estuary from inflowing rivers. Saltwater pushed along the estuary bottom by the incoming tide brings in other nutrients of marine origin. Currents and tides circulate fresh and salt water, distributing and, to a certain extent, trapping dissolved and suspended matter. Deposition of these substances fertilizes the estuary and plant life flourishes. This plant life includes grasses, rushes, sedges  of estuarine marshes, benthic algae (diatoms), epi-benthic algae, and eelgrass on intertidal sediments. Some plants are fed upon directly by fish and wildlife but most die and enter the food chain in the form of detritus or partly decomposed plant material. This detritus, suspended in the water and deposited on the bottom, is a high-quality food for consumers because of its high nutritional value. A number of studies have shown that many species of fish and invertebrates feed wholly or partially on detritus. Therefore, detritus feeders are the critical link between plant production and the production of higher consumers. Consequently, the ultimate ecological value of primary production in marshes occurs when detritus of marsh plant origin enters the food web of the estuary.

Estuaries include three habitat types: open water, intertidal mudflats and salt marshes which are discussed separately.

Discover how the refuge is working to conserve estuarine habitat...

Facts About Estuary

One of the most productive environments on earth

Encompasses ~70,400 acres (28,500 hectares) at mean high tide

Has three major habitat types – salt marsh, intertidal flats and open water

Last Updated: Mar 18, 2013
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