In the Pacific Northwest, some salmon species, which mature as a saltwater species but reproduce in freshwater, will use estuaries and other nearshore areas for long periods.
There are also many species, like blue crab, that live most of their lives in the estuary and then go out into the open ocean to reproduce. Estuaries have supported, and continue to support, the development of human societies for thousands of years. All this ecological diversity and productivity has supported humans for millennia. In south Louisiana, the Chitimacha tribes lived for thousands of years on the rich soils, prolific fisheries and game found in the Mississippi River Delta region.
Before roads were reliable means of transportation, rivers were often the safest and most efficient means of moving people and goods from place to place. It is no surprise then that many of our major modern — and ancient — cities are located on estuaries, with access to both land and sea making them centers of production and trade.
At least 30 species of fish use estuaries at some stage in their life cycle including snapper, flounder, mullet, sole, rockfish, kahawai, trevally, parore, red cod, gurnard, eel, salmon, whitebait and sharks. The life is diverse yet connected — interdependent for its own survival. Vital to the interdependence of life in estuaries is the feeding relationship, known as the food web. The estuary food web contains:. Detritus is predominantly made up of rotting plants such as mangroves, seagrass and rushes.
Mud-dwellers such as snails, worms and crabs play an important role in recycling the nutrients from the detritus within an estuary. They consume the detritus material and produce nutrient-rich waste. This causes plants to grow quickly producing more food and then detritus. Larger animals such as fish and birds consume the mud-dwellers, transferring nutrients further afield.
Estuary plants such as mangroves, saltmarsh and seagrass also provide a habitat for a range of organisms. The plants trap sediments coming into the estuary and therefore nutrients.
Filter-feeders such as snails, cockles and oysters live at the base of these plants. Shellfish use siphons, gills and cilia fine hairs to strain out food particles suspended in water. Worms and snails filter out food particles using their tentacles. The plants also provide protection and food the mud-dwellers for a variety of juvenile fish. Estuaries are also rich feeding grounds for migrating birds such as bar-tailed godwits, lesser knots and plovers. The kuaka or Godwit is found in a number of New Zealand estuaries.
As the water flows through the marshes, much of the sediments and pollutants are filtered out. This filtration process creates cleaner and clearer water, which benefits both people and marine life. Wetland plants and soils also act as a natural buffer between the land and ocean, absorbing flood waters and dissipating storm surges. This protects land based organisms as well as valuable real estate from storm and flood damage.
Salt marsh grasses, mangroves and other estuarine plants also help prevent erosion and stabilise the shoreline. Estuaries provide people with many opportunities for recreation including boating, fishing, swimming, diving, windsurfing and bird watching. Historically, estuaries have developed as urban centres because of their location on historical transport and shipping routes.
Estuaries are often the cultural centres of coastal communities and serve as the focal point for local commerce, tourism and recreation activities. Many also have special significance for local indigenous people. As transition zones between land and water, estuaries are invaluable laboratories for scientists and students studying the complexity of biology, geology, chemistry, physics, history and social issues.
These unique coastal environments also provide aesthetic enjoyment and the proven health benefits of green space for the people who live, work or visit estuaries for the many recreational activities. Tourism, fisheries, and other commercial activities thrive on the wealth of natural resources estuaries supply. The protected coastal waters of estuaries also support important public infrastructure, serving as harbours and ports vital for shipping, transportation and industry.
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