An Estuary is an enclosed body of water along the coast where freshwater from rivers meets salt water from the sea. Estuaries and the lands surrounding are places of transition from land to sea or fresh water to salt water. Although estuaries are influenced
greatly by tides, they are protected by land forms from the full power of ocean waves, winds and storms. Water is continually circulating in and out of estuaries. Tides create the largest flow of saltwater, while river mouths create the largest flow of freshwater.
Estuarine environments are one of the most productive in the world. They create more organic matter each year than the same sized areas of forest, grassland or farm land. The tidal, sheltered waters of estuaries support a wide community of plants and animals that are adapted to the lands edges of the sea. Estuaries provide rich feeding grounds for coastal fish and migratory birds and are spawning areas for fish and shellfish. They are also important in maintaining the quality of coastal waters.
Many different habitats are found in and around estuaries. These include shallow open waters, freshwater and salt marshes, swamps, sandy beaches, mud and sand flats, rocky shores, oyster reefs, mangrove forests, river deltas, tidal pools and sea grasses.
Plants
Plants that are found in estuaries have to adapt to salty conditions. Having too much salt can kill some types of plants. Some plants can absorb salt water and store the salt in special compartments, called vacuoles which are found in the leaves. An example of a plant that uses this is a pickle weed. Other plants like salt grass and alkali heath can push the salt out onto the surface of their leaves. Mangroves, wire rush, sea grass, sea rush, salt marsh ribbonwood, smooth cord grass, purple loosestrife, algae, sea primrose, sea lavender, flax, orchids, glasswort and remuremu.
Animals
A variety of animals are found in estuaries. The complex food web that is found in estuaries helps support a diverse range of animals. Decaying plants are eaten by microorganisms. The microorganisms are eaten by small invertebrates. Fish like carp and stickleback then eat these invertebrates. Many of the fish we eat depend on estuaries to keep their population growing. They are sheltered places where fish can have their young and let them grow before going out into the open ocean. Without estuaries, the number of fish in our oceans would decrease greatly. Sometimes water in certain parts of estuaries can dry up into mud flats. These areas are still home to mussels, shrimp, worms and other invertebrates.
They are also home to birds looking for a feed. Migrating birds such as geese use estuaries to feed and rest. Birds who are permanent residents of estuaries include the Great Blue Heron and the Great Egret. The Great Egret has long legs that they use to wade through the water. They are excellent hunting fish, wiggling their toes to attract fish. Different types of birds have different lengths of beaks, depending on what types of food they eat. This allows more birds to live in the same area because there is little competition for the same types of food.
Other marine life and wildlife found in estuaries include marine worms, shellfish, crabs, oysters, mud shrimps, harbor seals, river otters, Pacific staghorn sculpin, star fish, salmon, trout, crocodiles, snakes, dolphins, sharks, dugongs and perch.