Questions to ponder
· An area where conditions prevent the
growth of salt marsh plants in the intertidal zone is the
When fresh water pushes into an estuary
overriding the denser salt water, the saltwater enters the estuary along the
bottom and forms a
The result of water movement through the
estuary is cleansing and known as
· Which is an example of a stenohaline
· An organism that can tolerate wide ranges
of salinity are known as
· How can estuaries form?
· The estuarine environment is characterized as a ___________
Tides in estuaries do what?
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.
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.
. 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,
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
..and the dependency of so many important commercial and sport
fisheries on estuaries is one of the major economic reasons for preservation of
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.
Formation of Estuaries
Estuaries can form in
4 methods are:
Drowned River Valleys
San Francisco Bay
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
Pollution can also get trapped.
There are three types of producers in the estuaries..
Detritus...involves accumulation and decomposition of dead
Spartina sp. 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.
Terrestrial and freshwater vegetation that lived in the low
lying coastal regions during the ice age were killed as the advancing seawater
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.
The four regions of the marsh are..
Salt barren region
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
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
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
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!
1. How many miles of
shoreline are found in the USA?
2. Why are commercial
fisheries dependant on estuaries?
3. Define estuary.
4. Name 4 ways estuaries
5. What is a salt wedge?
6. What are some interchangeable terms with
7. Why do coastal nekton
take advantage of estuaries?
8. What are the three
types of producers in estuaries?
9. Why is the high rate
of food production possible in estuaries?
10. What are the 4 areas
of a salt marsh?
11. What are some of the
adaptations the cord grass has made to adapt to its environment?
12. Why is the statement
"the mud flat is a barren area because there is no visible plants on
is the trophic pyramid inverted in estuaries?
14. How is the role of bacteria and other
saprophytes in estuaries necessary for the productivity of the estuary to be