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What is so Important About Estuaries?

Why Are Estuaries Important

Estuaries – Where fresh and salt water meet

Why Are Estuaries Important?

An estuary is a place where a river meets the sea. It is a unique place of transition where freshwater and saltwater mix. Estuaries are vitally important systems on our planet. This is because they provide food and shelter for so many animals and plants.

Probably the Number one reason estuaries are important is because they provide a safe nursery ground for many species of fish and shellfish, including many that we like to eat. Without these nurseries, the numbers of adult fish would soon plummet.

Estuaries are also important for several other reasons:

  • Estuaries provide a great location for recreational activities such as boating, fishing and swimming.
  • Estuaries are a natural source of protection from storms and floods due to their wetlands, marshes, mangroves and coral reefs.
  • Estuaries provide habitat for many birds and other wildlife, including endangered species. There are more than 50 species of fish that live in estuaries part or all of their lives.
  • Estuaries are an excellent source of food, minerals, materials and medicines – some of the most valuable natural resources used by humans today were first discovered in estuaries (such as asphalt and penicillin).

Beyond serving as fish nurseries, estuaries are important to people and the environment. Estuaries provide us with food, jobs and recreational opportunities. Estuaries also help to protect coastlines from storms, floods and erosion by absorbing wave energy and reducing flooding impact.

In fact, many major cities are located on estuaries. These include New York, Boston, San Francisco, Seattle and Vancouver.

Types of Estuaries

Estuaries are classified into three types: drowned river valleys, bar-built estuaries and fjord estuaries.

A drowned river valley is formed when a river is submerged in a rising sea level situation. The river’s mouth or lower course is flooded and the water depth increases towards the head of the valley. The resulting bay or lagoon is often shallow and may contain islands, shoals and sandbanks. This type of estuary also occurs when a river has been dammed to prevent tidal waters from mixing with fresh water.

Bar-built estuaries are created when barrier beaches or islands form parallel to the coastline thus separating the estuary from the ocean. The barrier beaches and islands themselves are formed by wave action. sand and sediment accumulate over time as they are brought in by ocean waves. Rising sea levels are associated with the creation of bar-built estuaries. These sandbar-like structures allow saltwater to mix with freshwater creating brackish water typical of estuaries.

Fjord estuaries are the result of glaciation. Advancing glaciers create long, narrow, steep sided valleys with a shallow and usually narrow sill near the ocean. These valleys, left behind as the glaciers recede, fill with sea water. But as fresh water from the land enters the valleys, estuaries are formed. So, fjords, and the associated estuaries are found in areas once covered by glaciers; areas of Alaska, Washington State, Canada and also southern Hemisphere places like New Zealand and Chili.

Animals found in Estuaries

“Up to 80 percent of the fish that we catch spend at least part of their lives in estuaries.” – Jim Gerlach

Estuaries are partly enclosed coastal bodies of water with one or more rivers or streams flowing into them, and with a free connection to the open sea. The waters of estuaries are usually highly organic and rich in nutrients, making them ideal habitats for many animals.

The animals that can be found in estuaries include fish, shrimp, oysters, crabs, sponges, lobsters, sea anemones and birds such as egrets and herons. The most common animals found in estuaries are fish that prefer brackish water environments such as striped bass, flounder and Atlantic sturgeon. Shrimp is a very important commercial species found in estuaries. The shrimp and the crabs live in the water and they hide under rocks and in holes in the sand.  The fish eat the animals that live on the plants.  The herons and egrets stand in the water and wait for a fish to swim by. Oysters are commonly found in the muddy bottoms of estuaries.

Plants Found in Estuaries

The plants found in estuaries are adapted to tolerate the brackish conditions which occur where salt water is diluted with fresh water. The most common plants are salt-tolerant grasses, sedges and reeds. Some of the plants that live in estuaries are seagrass, pickleweed, and mangrove.

Seagrass is a flowering plant that lives underwater. Seagrasses help filter pollutants out of the water. They also provide shelter and food for fish and other marine life. Seagrasses can be found off the coast of every continent except Antarctica.

Pickleweed is a small, salty plant that can be found in salt marshes. Pickleweed has branches that grow from a single stem and small, fleshy leaves. Pickleweed roots help keep soil in place. They reproduce by sending out branches that take root when they touch the ground.

Mangroves are trees or shrubs that live in mangrove swamps where freshwater meets saltwater from the ocean. Mangroves have special roots that stick out of the water to breathe air. They also have thick, leathery leaves and prop roots to keep them stable during storms. Mangroves are home to many species of birds and fish

Estuaries and Coasts

The word “estuary” comes from the Latin word ‘aestus’, meaning tide. Estuaries are where rivers meet the sea; they are partially enclosed by land but have access to open ocean. They are also where fresh water meets salt water.

Estuaries are amazing. The sea is a wilderness where only the fittest survive. But estuaries offer safe harbor for many species. Estuaries are special places, too, where freshwater meets saltwater as rivers make their way to the ocean. Here, the water is neither one nor the other. In estuaries around the world, we find rich biodiversity: more species live in estuaries than any other habitat on Earth except tropical rainforests. Estuaries are nurseries for crayfish, crabs, shrimps and young fish. Migratory birds use estuaries as rest stops during their epic journeys around the world.

Estuaries help keep the ocean clean. They are lined with marshes and sea grasses that filter water flowing to the ocean. But as far as something flowing out of the ocean, estuaries act as a buffer protecting inland areas from the worst effects of coastal storms, especially hurricanes.

Characteristics of Estuaries

The main environmental factors that affect estuaries are fresh water input, salinity, and tidal action. The balance between these three factors determines the type of vegetation that grows in an estuary and the types of animals that live there. These factors also influence each other: for example, if less fresh water enters an estuary as a result of drought, it will have a higher salinity level and different species of plants will grow there.

Estuaries are often divided into zones based on their depth or on the speed of their currents. The shoreline area is called the intertidal zone; it is underwater at high tide and above water at low tide. The shallow subtidal area is under water all the times; it is called the sublittoral zone when it lies just below low tide and the bathyal zone when it lies deeper than that. The deep open water beyond that point is called the neritic zone which is up to 200 meters deep.

The bottom line is that Estuaries are one of the most productive ecosystems found anywhere in the world.

Estuaries in Decline

protecting estuaries

Coastal seas and estuaries have been in an accelerated state of environmental decline for the last 150-300 years.

A recent study indicates that while degradation has been going on in coastal ecosystems due to human influence since Roman times, the decline has significantly accelerated in the last 150-300 years. 12 major estuaries were analyzed. From historical records, it is estimated that “65% of wetland and seagrass habitats have been destroyed, water quality has decreased significantly, and 90% of marine species have disappeared”. And there is no way around the conclusion that human activity has been the primary cause.

As human beings we need healthy estuaries. As mentioned, they serve as nurseries for many fish species. And it just so happens that many of these fish are the basis for a large part of our commercial fishing industry. And don’t forget that estuaries act as an important buffer zone against natural disaster. Unfortunately, it appears that estuary environments are not only shrinking but are also experiencing severe environmental degradation. Estuaries are critically important areas but there seems to be little public awareness or attention to this issue. Also, policy initiatives aimed at protecting and preserving them are seriously lacking.

The good news is that we know how to successfully manage these important ecosystems. We know that human exploitation of these important resources is the main issue. And we know that estuaries can be restored. By stopping habitat destruction, cutting back on resource exploitation and eliminating the sources of pollution entering the system, restoring these areas to more pristine and productive conditions is very possible. Do we have the will to do it?

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