A barrier island is a coastal accident composed of sand and other sediments. It might be narrow, of low height, and parallel to the coasts, but separated from them. In general, barrier islands appear like chains that can be composed of a few or several islands. These chains might extend for many kilometers. Their formation depends on many oceanic factors, which can easily form them and then make them disappear, such as waves, tides, streams, and other physical factors of the ocean. They are significant because they protect the coasts and lands from erosion and the damage caused by the storms. Besides, the barrier islands usually provide habitat for many different species. Their shape is very dynamic. They form, get eroded, change position, change their size, disappear and appear again through time.
An estuary is a region where freshwater mixes with seawater. These are unique ecosystems where many different species can live in.
A marsh is a depressed area saturated and cover by water, where many aquatic plants grow.
A sea wall is a structure that is placed on the coasts and that protects them from erosion, specifically, wave erosion. These structures are not separated from the land.
Barrier islands represent a class of coastal landform composed of sand and sediments that forms parallel to the coast. These islands are constantly changing, being shaped by different factors which include water currents (ocean currents), erosion and waves. Some of the most important parameters that influence the length and width of barriers are tidal range (i.e., the height difference between high tide and low tide), wave energy (i.e., the energy restrained from oceanic waves), the amount of sediment supply and sea-level trends.
Five conditions are required which are 1)there must be random mating,2)the population must be very large,3)there cannot be no movement into our out of the population, 4)no mutations,5)no natural selection.
