This video, we're going to talk about estuaries. An estuary is defined as a coastal, transitional area between the end of a river and an ocean. The river is always going to be flowing into the ocean, and estuaries are prevalent as they're found along coastlines worldwide. An estuary is going to contain both freshwater and saltwater, making estuaries somewhat of a unique aquatic biome. It allows estuaries to support a wide variety of species, species that rely on saltwater, but also species that rely on freshwater. Additionally, it supports species that require very specific concentrations of both freshwater and saltwater. Often, in estuaries, the denser saltwater is going to occupy the bottom layer of the water, while the lower density river water, which is freshwater, will be found at the surface of the water.
Notice in this image in the top left, we've got this aerial view of an estuary where you can see that the river is flowing in this particular direction, indicated here, into the ocean. This entire region would be the estuary. During the high tide, the ocean water can kind of come upwards in the river, higher like this, and so there will be higher salt concentrations during the high tides. But then during the low tide, the ocean water kinda falls back down and the freshwater from the river kinda takes over these regions here. As a result, the saltwater in these regions can be quite dynamic.
Now, these estuaries often have a very high aquatic productivity that supports a wide variety of different species. This here concludes our brief lesson on estuaries.