Estuaries 
Estuaries are of immense importance and are frequently areas of high fertility and large phytoplankton and zooplankton populations. Its been estimated that 60 to 80 % of the commercial marine fisheries resources depend on estuaries for part of or all of their life cycle.
An estuary is a semi-enclosed
coastal body of water which has free connection with the sea, thus is strongly
affected by the tidal action. Sea water is mixed with freshwater from land
drainage. The estuary is not part of the coast but is a coastal feature with a
continuous exchange of water between it and the sea. It typically contains
marine plants and animals having anatomical, physiological, or behavioral
adaptations to the changing conditions found in estuaries. They produce
numerous kinds and vast amounts of sport and commercial fishes and provide
numerous other ecological services of direct and indirect value to humans.
Positive estuaries...the precipitation and runoff exceed evaporation and sea water is diluted.
Neutral estuary...runoff+prec. =evaporation
Negative or inverse estuaries...almost no freshwater runoff.
Currents in the estuaries come from tides, river runoff, transport by wind generated surface waves, direct stress by wind on water surface , variations in density distributions, and internal waves.
Plants and animals possess different tolerances for such physical parameters as salinity, consequently an estuary may be divided on the bases of salinity, each part corresponding to certain biotic classifications.
Several terms are used
interchangeable with estuary: wetlands, lagoon, slough, salt marsh, marsh,
swamp. The term wetlands refers to land on which water dominates the soil
development and thus the types of plants and animals that will live there. The
term lagoon is the region between a barrier island or spit and the mainland, a
slough is a shallow estuary with large areas of the bottom exposed during low
tides, a salt marsh is a shallow tidal estuary protected from ocean waves and
inhabited by plants and can withstand submergence. The term marsh (used
interchangeable with salt marsh) but in precise sense refers to a region with
zero salinity upstream from a salt marsh. A swamp is a lowland area saturated
with water often quite large and farther inland.
It is common for coastal nekton to use estuaries as nursery grounds where young growth stages can take advantage of the protection and abundance of food. Since man often harvests such species offshore, the vital life history and energetic connections with the nearby estuary have not always been appreciated and the dependency of so many important commercial and sport fisheries on estuaries is one of the major economic reasons for preservation of these habitats. Its estimated that 60-80% of the commercial marine fisheries resources depend on estuaries for part or all of their life cycle.
The intertidal and adjacent shallow water zones are the most productive and most important and also the 1st to suffer the ill planned encroachment of man Estuaries tend to be more productive than either the sea on one side or the freshwater drainage on the other.
The estuary is a nutrient trap, partly physical and partly biological. Retention and rapid recycling of nutrients by benthos, formation of organic aggregates and detritus, and the recovery of nutrients from deep sediments by microbial activity, and deep plant roots create a self-enriching system. Pollution can also get trapped.
There are three types of producers in the estuaries...macrophytes, benthic microphytes, phytoplankton.
Detritus...involves accumulation and decomposition of dead materials.
Spartina is the major producer and the microbial enriched grass detritus feeds consumers in creeks and sounds. The role taken by eel grass Zostera or seaweeds in colder water, Turtle grass (Thalassia) in warm waters...make contributions to productivity of sub-tropical and tropical lagoons. These sea grasses often support a large population of epiphytic algae and small fauna.
Spartina
Terrestrial and freshwater vegetation that lived in the low lying coastal regions during the ice age were killed as the advancing seawater moved inland. Grasses that could thrive in brackish estuarine environments colonized the salty mud and as the the roots of the plants grew down, trapping more particles, the estuary grew. With each tide, planktonic larva of clams, mussels, crabs and worms settled among the plants and fish, birds insects and animals migrated to the young estuaries for food and living space.
The salt marsh community is a relatively flat grass covered coastal area occurring within the estuarian ecosystems in temperate climates. Its partially flooded by tides (tidal march or wet land). The marsh can be thin or very wide and is one of most productive habitats in the marine environment. Vast quantities of food are produced by marsh grass (Spartina) and algae that live on the surface of the mud. Photosynthesis. is fastest at low tide and an ample supply of nutrients (nitrates, phosphates and sulfates) in the estuary make a high rate of food production possible. (nutrient rich water bought in each high tide). Blue-green algae convert atmospheric Nitrogen into nitrates .
Salt marsh producers grow rapidly and absorb minerals at a fast rate. Spartina grass and other marsh producers have a short life. Floating seaweed and debris are dumped onto the marsh at high tide and as this and the marsh grass dies, teeming masses of bacteria break down the complex plant material into detritus. Isopods, insects, fiddler crabs, marsh snails eat the decaying plant tissue, digest it, and excrete wastes that include nitrate, phosphate and sulfate. By quickly converting the decaying material into inorganic material, these detritus feeders speed the growth of living marsh plants.. Each tide carries much of the detritus and minerals into the offshore water with phytoplankton using the minerals, clams, mussels, worms, and sponges eat pieces of detritus. (these excrete minerals when they break down the detritus adding more..and this rapid cycling of minerals is a unique feature of the tidal salt marsh, making the high rate of primary productivity possible. Wetlands near cities also have an additional source of minerals for producers with the billions of gallons of sewage/treated and untreated, discharged into coastal waters (as well as PCBs bacteria, viruses heavy metals, which can be ingested by marine organisms and be passed on to humans).
Food web
Communities within estuaries are linked by overlapping food chains as energy flows from primary producers to consumers. (food wed). Many primary producers are first converted by bacterial decomposition into organic detritus which serves as a major food source for the majority of consumers living in the estuarine community. An important group of primary consumers living in estuaries are animals that feed on plankton and these are the most abundant species of vertebrates in estuaries because of the large supply of food available to them. The carnivores (predators) occupy the highest level obtaining energy by eating animals that feed on plankton and detritus.
Predators are important to the estuary because of their end position in most consumer food chains. Part-time and full time residents feed there. Many migrating animals stop over for refuge and food in the estuary thus exporting the energy to other environments. One aspect of the estuary food web is that there are more different species of consumers than species of primary producers. A few provide nutritional needs to many. Thus the usual trophic pyramid is inverted because most carnivorous species are at the top of the food web!
Reading With Estuary Questions
2
1.What conditions do estuarine
plants and animals have to put up with?
2. What can upset the balance of estuarine organisms?
3. Why are estuaries
special to
4 List some producers
and consumers of the estuaries.
5. How is
6. What percent
decline in estuaries has been noted from Sebastian inlet to St. Lucie inlet
along the