Estuaries: characteristics, types, flora and fauna

These are the main characteristics of estuaries :

• It acts as a refuge for many animal and plant species that depend on these to live, as well as to feed and reproduce.
• They are classified depending on the area where the water that flows from the rivers ends since it can end up pouring its water into oceans, bays, ports, inlets, lagoons or channels.
• At the mouth of the river, once fresh water is brought into contact with salt water , a high degree of turbidity occurs.
• They are areas sometimes destined for recreational, tourist or scientific use.
• Estuaries are characterized by being among the most productive ecosystems on the planet, since, compared to other areas of the same size, estuaries produce a greater amount of organic matter. That they are so productive is because nutrients arrive from the land that have been washed away by rivers and on the other side there are nutrients from the sea.
• Being a semi-closed system in it there is a great exchange of materials of all kinds with neighboring ecosystems.
• They are shallow areas, this characteristic makes the light that comes from the sun easily penetrate through the water, producing photosynthesis more actively.
• In them are many of the species that humans consume, some crustaceans, mollusks, some species of fish, among others.
• It has the capacity to retain considerable volumes of water, avoiding flooding and damage to the coast when strong storms occur.
• Sometimes the flow of water that comes from rivers carries a greater volume, therefore this causes sediments and pollutants to be removed, making the water stay cleaner.

Next, the most characteristic species of the area will be shown, both those that are part of the flora and those that are part of the fauna.

Each type is determined by the result of the volume of water coming from a river during the tide and the volume of the tidal water. Knowing this, we can find the following types of estuaries :

• Saline wedge estuary: occurs when the amount of river water is greater than the amount of tidal water. Therefore we would have a mixture with a thin transition layer between the river water in the upper part and the tidal water wedge in the lower part.
• Highly stratified estuary: The amount of fresh water entering is still greater than that of tidal water, but not as much. The mixing of this estuary would end up with a more saline upper layer of water, since the waves cause the tidal water to go to the upper part, thus mixing with the river water.
• Slightly stratified estuary: the amount of river water is smaller than the amount of tidal water. Salinity changes both in the upper and lower layers of the estuary, due to the very turbulent tidal flow.
• Vertically mixed estuary: practically the volume of fresh water is negligible with respect to that of the tide, the tide dominating the estuary with a homogeneous salinity, in addition there is no vertical stratification in the water column
• Reverse estuary: in them there are no contributions of water from the rivers, but they are in areas with high evaporation. This high evaporation causes the salinity to increase due to the loss of water and the sinking of the water occurs due to the increase in density as it is more saline.
• Intermittent estuary: these are those that can be of one type or another depending on the precipitation, since they are in an area where the precipitation is highly variable.

Estuaries are made up of a very varied flora. The most representative species in these areas are aquatic plants and among them are:

• Enea ( Typha domingensis )
• Junco (Juncus spp)
• Bijao ( Thalia geniculata )

Mangroves are also present in estuaries , these are made up of tree species resistant to brackish conditions and adapted to humid soils. There are about 70 species of mangrove trees , but the most prominent are:

• White mangrove ( Laguncularia racemosa )
• Black mangrove ( Avicennia germinanas )
• Red mangrove ( Rhizhophora mangle )
• Gray mangrove ( Conocarpus erectus )

Other vegetation associated with the mangrove and that is present in estuaries are sea ​​grasses , such as ( Thalassia testudium ). These grasses form walls in shallow, crystalline water substrates. Finally, we want to indicate that, in estuaries of one or two meters deep, receiving enough light can form a dense bed of bottom plants, or also called algae plain . And, of course, in estuarine waters there are phytoplankton too .

As with flora, we can also find a great diversity of animal species in estuaries .

• The smallest animals that inhabit this ecosystem are those that form zooplankton , we can find it in the water at night but, when the sunlight comes out, it hides in the lowest and darkest areas of the estuary. Zooplankton feed on suspended organic matter and phytoplankton.
• Zooplankton is consumed by estuary fish species , including herring, sardines, anchovies, etc., and they not only eat zooplankton, but also phytoplankton. Learn more about estuary fish in this other AgroCorrn article on Classifying Fish .
• In the group of estuarine crustaceans are the blue crab, the pistol shrimp and the prawns.
• Among the mollusks in estuaries are the black oyster and the piangua.
• Species of mammals and birds also inhabit this ecosystem. On the one hand, species of mammals such as the crab raccoon and the otter and, on the other, species of birds such as the boobies, the cormorant, the pelican and the night herons.
• Among the reptiles that live in estuaries, there is a special species that lives in this ecosystem and is in danger of extinction. We are talking about the alligator and this is one more reason why it is so important to conserve and protect these natural spaces.

In short, after seeing all the characteristics of estuaries , we can conclude that they are very important ecosystems for living beings and are of special interest for scientific studies. But these are constantly threatened by anthropic activities or activities carried out by people:

• They are being contaminated by pesticides, industrial and household waste.
• Intensive fishing and farming are other damaging factors. Learn more about this problem in this other article on Overexploitation of natural resources: causes and consequences .
• All kinds of constructions that are made in its environment, such as structures that are used to control the flow of fresh water, such as dams, cause the natural balance of the system to be altered.
• The recreational use that is given to it for fishing and hunting can have a strong impact if the prohibition laws are not respected. The laws of closure are those that determine the time in which certain species can be hunted and fished so as not to alter their balance and that of the ecosystem.