An estuary is a partly concealed body of water where fresh water from rivers and canals mixes with the salty and brackish waters of the open sea. Estuaries facilitate the development of various land forms at the coast such as bays, lagoons, harbors, inlets and fjords.
Estuaries are usually rich in nutrients due to the mix of fresh and salty waters. This facilitates the thriving of a unique ecosystem comprising organisms such as fish, birds and even plants.
-Estuarine food webs
Because of the confluence between salty and fresh waters in an estuary, the environment is quite hostile. Such environments support the growth of a selected few plants such as seaweeds and photosynthetic phytoplankton that absorb nutrients, produce a lot of food and grow very rapidly. Because of the competition for the oxygen and sunlight, the vegetation usually dies off rapidly, leaving masses of dead plant organic detritus. Bigger microorganisms such as the zooplankton feed on the phytoplankton, reducing their number. In return, bigger estuarine animals such as filter-feeding worms feed on the zooplankton and the decaying organic matter (detritus), thereby closing the food web in the estuarine ecosystem.
According to the Te-Ara Encyclopaedia of New Zealand authored by the New Zealand government estuaries are generally hostile environments because of the high presence of salty water. In order to cope well with this kind of ecosystem, the plants need to be able to:
– Accommodate environments with varying levels of salinity.
– Adjust to strong sea currents and tides.
– Acclimatize to varying exposure to the sunlight and winds.
– Cope with low oxygen (anoxic) levels in muddy soils.
The most common estuarine plants are:
-Sea grass
Sea grasses are flowering plants that are able to live submerged under sea water. These grasses grow and spread in a meadow-like fashion resembling normal grass growing on a rolling hill or plain. Sea grasses are able to photosynthesize. They thus occur in shallow and muddy coastal and estuarine waters anchored in the sand. Sea grasses form extensive beds under the sea water. These beds might be composed of a number of sea grass species. The sea grass also traps sediments due to the slow movement of the water. This benefits the coral reefs since sediments in the water are reduced. Sea grass provides the following benefits to estuarine environments:
– Their leaves slow the fast underwater currents thus promoting sedimentation.
– The sea grass plants stabilize the seabed due to their dense network of roots.
– They also provide a good breeding ground for some species of small fish.
-Mangrove
Mangroves are various species of trees and shrubs that grow to medium height in coastal and estuarine zones in the tropical and subtropical regions of the world. The term “mangrove” is mainly used to refer to all the plants that grow in a region designated as a mangrove swamp. The mangrove swamp biomes or mangals are characteristic in areas where there is a high sediment deposition (such as estuaries). These sediments settle in these ecosystems because they are protected from the violent wave action in the open sea. Mangrove habitats provide the following benefits to the environment:
– The mangrove swamps assist in harboring microorganisms in regions susceptible to high tide fluctuations, due to their resistance to tides.
– The mangrove trees are able to overcome the limitations of growing in anoxic waters.
– Mangrove roots help in slowing water flow, thus promoting sedimentation in these mangal zones.
– Mangrove swamps protect the coastal soils from soil erosion, high tides and even natural phenomena such as hurricanes and strong winds.
-Salt wort
This is a name given to various species of flowering plants that thrive along the coastal waters and the estuarine zones. One of the types of salt worts is salsola. These plants thrive in salty environments. They therefore are plentiful in coastal environments.
-Cord grass
Cord grass is also known as Spartina. They are a number of grass species which grow in large colonies in brackish or salty waters, especially at the coastal areas. Different grass species usually form hybrids when they come into contact with each other. They also form dense colonies along coastal areas, which grow very rapidly. Cord grasses are used as food plants by selected larvae.
-Salt Marsh Plants
This is a collection of a number of grasses and other plants that can grow in conditions of high salinity. These plants can also be referred to as halophytes. These plants colonize saline environments due to their ability to be salt-resistant or being able to metabolically avoid salt altogether. The plants are able to excrete excessive salts from their systems by concentrating these salts in their leaves. They usually concentrate such salts in leaves that are about to die.
