Energy Flow and Productivity
Transition Habitats
Subtidal Ecosystems

Fjords, another estuary type, are formed by sediment and other material left behind by retreating glaciers. Like rivers, glaciers create valleys along the coast that are filled when the sea level rises.

Others, known as bar-built estuaries, are formed when sand and sediment build up along coastlines and create giant sand bars or barrier islands that form semi-enclosed basins.

Finally, near active continental margins, tectonic estuaries are formed from the sinking of land caused by the movement of the earth crust rather than a change in sea level. San Francisco Bay is an example of a tectonic estuary.

Transition Habitats - Estuaries
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