Tides are the daily or twice daily movement of water in and out of an estuary or coastal area. There are high and low tides. High tides are determined by the high water mark on the shoreface, the sand on the beach. High tides bring high salinity water and add nutrients to the estuary, flushing away waste products, impurities, or even pollution. As the high tide gradually falls to its lowest point, it becomes the low tide, and the cycle starts over again.
Winds are movements of air which blow from offshore, moving seawater into the estuary.
Winds also blow from the land toward the sea, moving water out of the estuary and drying areas which are normally wet. When an ecosystem or a habitat has many different plants and animals it exhibits biodiversity . Biodiversity contributes to the stability of ecosystems. If there are many producers, consumers and decomposers, there is less chance that loss of one species will impact the entire ecosystem. Estuarine animals and plants must tolerate changing salinities and other conditions such as fluctuating temperature, water level, currents, and levels of oxygen.