Salt Marshes,
Marshes, Estuaries,
Estuaries, and
and Mangrove
A Dominic Pesavento
By Dominic Pesavento
Transition Ecosystems
Estuaries, salt marshes, and Mangrove forests share quite a few traits. One such
unifying characteristic is that they are transitions between two habitats. In the case of
estuaries, it is where the ocean meets the river. In the case of Salt marshes and
mangrove forests, it is where land meets the sea. All three can often be found near
the mouths of rivers.
Salt Marshes generally include channels, called tidal creeks, that fill and
empty with the tide. This meandering of creeks can create a complex
network of channels within a salt marsh. Water is moved up and down these
creeks by fluctuating tides once or twice each day, gradually sculpting the
marsh into a gently undulating landscape. Tidal creeks are usually bordered
by natural levees, beyond which lie marsh flats. These includes salt pans,
which are small basins that periodically collect water that eventually
evaporates, leaving behind a layer of salt. The whole landscape is flooded
during the highest tides and drained during the lowest.
Mangrove Trees of different species are generally distributed according to
height within the intertidal zone. For example, in mangrove forests near Rio
de Janeiro, Brazil, the mangroves growing closest to the water belong to the
genus Rhizophora. At this level in the intertidal zone, Rhizophora is
inundated by high tides. Above it grow other mangroves such as Avicennia,
which is flooded by the average spring tides, and Laguncularia, which only
the highest tides touch.
Salt Marsh Cross Section
Mangrove Forest
Human Influences
Estuaries, Salt Marshes, and Mangrove forests are all extremely vulnerable
to human interference, due especially to the desire for seaside living. Since
such building sites are limited, salt marshes are often dredged and filled in
for land development. Cities such as Boston, London, and san Francisco
are built on estuaries, as cities benefit from access to the sea. Because of
this, estuaries are often contaminated by the organic waste we produce
and depleted of oxygen by such discharge.
Temperature/ Climate
The temperatures of estuaries, salt marshes, and mangrove forests are
highly variable. Since they are generally shallow, particularly at low tide,
water temperature varies mainly with air temperature.
The temperature of an estuary may change with each high and low tide
,since the temperatures of seawater and river water may differ.
Salt Marshes at high latitudes may freeze in winter, in contrast to
mangroves, which grow where the minimum temperature is around 20
degrees Celsius and the shallows can heat up to over 40 degrees Celsius.
Range of Salt Marshes and
•Salt Marshes are found at mid to high latitudes, while mangrove forests are
generally found in tropical and subtropical environments, where the minimum
sea surface temperatures are > 16 degrees celsius.
Estuaries, salt marshes, and mangrove forests experience significant
fluctuations in tidal level. Consequently, the organisms in these
environments are exposed to highly variable light conditions. They may be
exposed to full sunlight at low tide and very little light when the tide is high.
Because of shifting currents, the waters of these areas are often turbid.
These currents keep fine organic and inorganic materials in suspension.
Intertidal organisms are often adapted to an amphibious lifestyle (partly marine, partly
terrestrial). As such, all are adapted to periodic exposure to air, though some species
are better equipped than others to withstand this exposure.
This produces one of the most noticeable intertidal features, zonation of species.
Species living at the highest levels of the intertidal zone are exposed by almost all
tides and remain exposed the longest. Others are exposed during the lowest tides
only, maybe once or twice a month, or even less frequently. Microtopography also
has an influence on the distribution of intertidal organisms. Tide pools support very
different organisms than do sections of the intertidal zone from which the water drains
completely. Another habitat is offered by the channels in which the seawater runs,
during the ebb and flow of the tides.
Substratum also affects the distribution of organisms. Hard, rocky supstrates support
a different biota than softer substrates such as sand or mud. On soft bottoms, most
organisms are burrowers and dig shelter for themselves within the sand or mud
bottom. Study of these organisms requires separation of them from the mud/ sand.
An obvious profusion of life on rocky shores is visible, since most of the organisms
attach themselves to the rocks (examples: Sea stars, barnacles, Urchins, etc.)
Salt Marsh food web
Little tidbit
If you were to scoop up just one teaspoon of mud from a North
Queensland, Australia Mangrove Swamp and look at it under a very
strong microscope, you would find that it contains more than 10
billion bacteria - that's among the highest found in marine mud
anywhere in the world!
Bacteria helps break down leaf litter and other bits of natural material.
Lots of bacteria tells biologists that these swamps are producing lots
of leaves and other sources of nutrition for plants and animals,
making Mangrove Swamps an immensely important coastal habitat.
Salt Marsh Fauna
Salt Marsh Flora
Estuary Fauna
Estuary Flora
Mangrove Forest Fauna
Mangrove Forest Flora
Salt Marshes, estuaries, and
Mangrove Forests.
While they may not offer the greatest species diversity, there certainly
is an abundance of organisms living in these environments, especially
fish, birds, and invertebrates.
Like other ecosystems, they are often harmed by humanity for the
sake of housing, farming, and other endeavors.
These transitional biomes can be found throughout the world and
offer many microhabitats for the species that dwell in them.
There’s a bit more to these ecosystems, but not a lot of time to
discuss everything, such as more emphasis on water movements.
Thank you and good day.
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