Estuaries can be found all over the world; both inland and on the coast. This is in all different climates and climatic zones. In estuaries found in temperate or polar regions, there are high temperature differences which can result in a low number of plants and animals. In tropical areas, an estuaries water temperature is much more stable and the number of plants and animals is less affected.
Tides
Tides are the main factor that affect estuaries. Tides are a vital role in having a healthy estuary. They flush out the systems and provide nutrients to keep the food webs functioning. On the other hand, tides create constantly changing conditions of the exposure to air and also the inundation of water.
Earth’s gravity holds our oceans to its surface. At the same time, the sun and moon’s gravity forces pull on the oceans. Water on one side of the Earth is pulled towards the moon creating a tidal bulge. On the opposite side of the Earth, another tidal bulge occurs because the water on that side is further away from the moon, therefore is not pulled as strongly towards it as the Earth is. As the Earth rotates, different parts on the planet’s surface experience the tidal bulge. This means the water level changes. The daily rise and fall of the oceans are called tides.
When the waters rise along the coast, tides push seawater into estuaries. When tides ebb, the water flows back out to sea. Tides rise and fall on a 24 hour cycle. Each day, estuaries can have one or two high tides, as well as one or two low tides. Animals and plants in estuaries have to adapt to the daily change of water levels, otherwise they won’t survive.
As the tides rise and fall, the foreshore is exposed to the elements and are flooded by tidal waters. This is an alternating wet and dry condition. Organisms must also adapt to the waves that are in a constant action in this zone.