Estuaries

  Estuaries 

 

Characteristics

Estuaries are partially enclosed bodies of water where freshwater (water without salt) meets salty ocean water. Bays, inlets and ocean-flooded river valleys are all examples of estuaries

Estuaries are divided into four types, depending on how they are formed

1. Coastal Plain Estuaries are formed by the sea level rising and filling an existing river valley. Examples of this are the Chesapeake Bay in Maryland and the harbor in Charleston, South Carolina

2. Tectonic Estuaries are caused by the folding or faulting of land surfaces. These estuaries are found along major fault lines, like the San Francisco Bay area in California

3. Bar-built Estuaries form when a shallow lagoon or bay is protected from the ocean by a sand bar or barrier island. Examples of these are found along the Eastern Seaboard and the Gulf Coast of North America

4. Fjords are U-shaped valleys formed by glacial action. Fjords are found in areas with long histories of glacier activity, like northern Europe, Alaska and Canada

Most of today's estuaries formed because the sea level has slowly risen during the last 18,000 years, drowning river valleys and filling in glacial troughs

Estuary Life

Estuaries are home to an astonishing variety of plants and animals and important in the lifecycles of many more. Crabs and clams of many species call these fresh and saltwater mixing zones home, each finding the salinity (saltiness) that suits them best

Horshoe Crabp

Filter feeders are found in all parts of the estuary. They are creatures that pull small bits of organic material, like plankton and larvae, from the water as it moves past them. Horseshoe crabs are one of the older inhabitants of coastal estuaries, living happily and largely unchanged for millions of years

Boring Sponge

Oysters blanket the estuary floors in areas where they use foot secretions to cement themselves to the substrate. Not only are these oysters a rich food source for us, but they are also important food sources to many estuarine creatures. Predatory snails, including Oyster Drills, whelks, sponges, especially the Boring Sponges, and fish all find oysters a tasty treat

The Black Drum has jaws powerful enough to crush adult oyster shells

Leidy's Comb Jelly is a jellyfish that eats oyster larvae

  Salt Marshes

Salt marshes form in shallow, quiet water, where the water is salty and still enough for the suspended particles to settle to the bottom. These marshes are some of the most productive lands in the world and produce so many organic nutrients that their influence can be seen far out into the coastal ocean waters. Marshes are based on one plant, the Saltmarsh Cordgrass, which helps stabilize the environment so that many other plants and animals to move in. Other plants including Cordgrass, Saltmeadow Grass, Blackgrass, Bullrush and Sea Lavender add color and variety to the marsh and grow in zones according to their tolerance (or ability to handle the saltiness) of the tidal water. Among the grasses, mats of algae grow in the upper layer of soil. Crabs, snails, insects and muskrats (partially aquatic rodent) are common inhabitants. Snakes and turtles abound, and fiddler crabs pop out of their burrows to find dinner after the tide goes out

Birds such as the Northern Harrier (marsh hawk) and the marsh hen are also common to salt marshes. Tall, leggy herons and the white snowy egrets wait patiently along the tidal creeks for small fish to swim by. The majestic bald eagle has become much more common in recent years and can often be seen perched at the marsh's edge, or dining on a fish. Marshes are also important stopping-places for migrating birds as well. Every autumn and spring, thousands of ducks and geese find temporary refuge during their travels

Mangroves take over from salt marshes in the lower latitudes, filling many of the same functions, although they aren't as productive. The dense and spreading roots of the mangrove trees provide sanctuary for fish, reptiles and insects. Thick foliage gives birds plenty of places to nest or perch while searching the waters below for food. Mangroves also help protect the shorelines from erosion. Beds of Eelgrass are a very important part of the estuarine ecosystem

 Humans & the Environment

Throughout history, we have depended on estuaries for trade, food and shelter from the sometimes-violent open ocean water. Some types of estuaries are better suited to this than others. The Chesapeake and San Francisco Bays are home to large, economically and militarily important harbors, where many, many ships pass each year

Some estuaries are quite deep, depending on how they were formed. Others have to be dredged often because the rivers that feed them carry so much silt and sediment that the deep shipping channels slowly fill in

Estuaries are home to a great many different plants and animals that we depend on for food. A very large number of commercially valuable fish return from the ocean to spawn in the protected waters of saltmarshes and mangroves. Oysters, clams and other shellfish thrive in bays and inlets, as do many species of crabs and fish

Any trash or sediment in a river naturally ends up in an estuarine area, since the current of the river slows here due to widening or running into the tidal force of the ocean. This pollution can have long-term impacts on the health of the creatures and plants that live there. Chemical contamination can linger in bottom sediments for years and has caused many areas to be closed for fishing until the chemical has been broken down. Excessive loads of silt and other sediments caused by erosion can suffocate bottom-dwelling plants and animals. Disruption of the flow of a river, due to damming and irrigation, can cause salty water to move farther upstream than it normally does, with devastating consequences for fresh-water species that cannot move upstream and out of danger. Many productive commercial fishing areas depend on phytoplankton nurtured by the seaward flow of clearer water, which in turn nurtures the fish. This rich outward flow may have a great deal to do with the overall health of continental shelf ecosystems

Another danger that estuaries face is development. Increasing populations are looking for places to expand, and what was once considered marginal land is now quite valuable, economically speaking. Wetlands are being filled in and mangroves destroyed in the name of development for housing and industrial purposes, and it is estimated that 215 million acres of estuarine habitat has been lost this way worldwide. Not only do we lose primary habitat for many animals and plants, but an important buffer zone is lost as well. Wetlands are remarkably good at breaking down nitrogen compounds and metals, both through plant action and hungry microbial communities.

 

good luck 

Mohamed Hassaan