Transcript MANGROVE ECOSYSTEMS

Biology of
MANGROVE
Mujizat Kawaroe
Marine Biology and Biodiversity Laboratory
Department of Marine Science and Technology
BOGOR AGRICULTURAL UNIVERSITY
Mangrove
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The Shorter Oxford Dictionary describe the word
"mangrove" as obscurely connected with the Portuguese
word "mangue" and the Spanish word "mangle" and the
English word "grove" and it dates its origin as 1613.
Marta Vannucci in her book "The Mangrove and Us"
points out that the word is neither Portuguese nor
Spanish and, after an exhaustive search, she concludes
that the word "mangue" derives from the national
language of Senegal. She comments that it was
probably adopted by the Portuguese, and later modified
by the Spanish, as a result of their exploration of the
coast of West Africa.
Mangrove
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The term "mangrove" has been applied historically to plants which live in
muddy, sand, wet soil in tropical or subtropical tidal waters.
In the nineteen sixties the term "mangal" was used for a community of
mangrove plants and the term "mangrove" for the plant species making up
the forest.
The terminology has tended to fall into disuse recently and term such as
"mangrove forest", "tidal forest" and "coastal woodland" have begun to
appear from groups of evergreen plants possessing marked similarities in
their physiological characteristics and structural adaptations to habitats
influenced by the tides.
The scientific literature is divided broadly into studies of the biology of
individual species of plants or animals in the mangroves and the study of
communities that may involve just plants or the relationship between plants
and animals.
The present intention is to sketch the most important features of mangroves
and mangrove communities in such a way that they can be understood by
the interested user.
Mangrove
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Mangroves can be trees, shrubs, palms or ground ferns growing in
the zone between high and low tide. Every kind of plant has a Latin
name or latinised scientific name and mangroves are no exception.
The Swedish naturalist, Carl von Linne (Linnaeus) in 1735 devised a
system for classifying plants and animals in systematic way.
Linnaeus assigned each different kind of organism a latinised
double name consisting of a genus name followed by an exclusive
species name. This system is known as binomial nomenclature.
The classification of plants divides them into various categories,
based on increasing degree of similarity. The largest categories are
division, which are subdivided into classes, order, families, and
genera. Each genus may contain only a single species or many
closely related species. Biological species are physically and
genetically similar to the extent they may interbreed to produce
viable offspring.
Mangrove
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There are approximately 70 species of true mangroves of which
some 65 contribute significantly to the structure of mangrove forests.
Approximately 15 species occur in South-East Asia, approximately
15 species occur in Africa, and approximately 10 species occur in
the America.
There are nineteen plant families with mangrove representatives
and only two families which are exclusively mangrove.
There are no order or higher ranks that are exclusively mangroves.
Mangroves are not a single genetic group but represent genetic
adaptation of a large variety of plant families to a particular
environment.
In case of plant family, Rhizophoraceae, often considered to be a
true mangrove family, only four of its 16 genera inhabit a mangrove
habitat.
Mangrove
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Extensive mangrove stands require a layer of earth or sand, usually
deposited by rivers and flood tides and shores free of strong wave and
tidal action. The also require salt and brackish water.
Mangroves are often characterized by aerial roots, seedling that
germinate on the tree and buoyant seeds that can be dispersed by
water.
Mangroves are often found in regions such as estuaries, embayments
and broad muddy tidal flats where the local terrain has led to the build
up of soil.
They prefer sheltered places where tidal and wind are not too
destructive. The conditions in which mangroves grow also influence
their characteristics for survival, their size and the pattern in which
they congregate.
On a global scale mangrove distribution is influenced by the presence
of warm and cold oceanic currents.
Tidal Inundation
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Mangroves are facultative halophytes which means salt water is not a
physical requirement for growth. Most can grow well in fresh water, but
mangrove communities are not usually found in strict freshwater
environments.
There are two possible explanations. Most strict freshwater habitats exist
where tidal inundation does not occur. Although not a direct physical
requirement, tidal fluctuation plays an important indirect role in mangrove
distribution.
Tidal fluctuation results in the reduction of competition due to alternating
wetting and drying, transportation of relatively clean water and nutrients in,
exporting wastes, detritus, and sulfur compounds, effective dispersal of
propagules. Where evaporation is very high, tidal fluctuation wash excess
salt away preventing excessively high soil salinity concentrations. Due to
the above factors, mangrove systems reach greatest development around
the world in low-lying regions with relatively large tidal fluctuations. In Red
mangroves,prop roots extend above most high tide levels. Black mangroves
are excluded as water depths increase. In freshwater communities other
species may out compete the mangroves for space.
Mangrove Forest
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Mangrove forests are best developed on tropical shorelines where there are
large areas available between high and low tide points. Large mangrove
formation are typically found in sheltered muddy shorelines that are often
associated with the formation of deltas at the mouth of a river system.
Mangroves can also be found growing on sandy and rocky shores, coral
reefs and oceanic islands. There are instances where islands can be
completely covered by mangroves. It is impossible to describe a typical
mangrove forest, as the variation in height and girth, even for the same
species, is immense, depending on the many factors that control growth
Mineral elemen
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All plants require various mineral elements to survive
and these are absorbed by the roots from the soil. Plants
require nitrogen, phosphorus, potassium, calcium,
magnesium, sulphur and iron. Sodium chlorides required
only in trace quantities and this poses certain problems
for mangroves due to high abundance of these two
elements in the sea water surrounding their roots. Other
trace elements required by the plants for successful
growth are boron, manganese, zinc, copper and
molybdenum.
Mangrove soil
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Mangrove soils are quite different from those that most other terrestrial
plants grow on. They are poorly drained, lacking in oxygen and are often
fine grained and rich in organic matter. In appearance the soils are often
clayey mud or sand.
Mangroves grow on waterlogged soils that are often lacking in oxygen.
These are known as anaerobic soils, literally, soil without air. The lack of
oxygen in the soil is due to the slow rate of diffusion of oxygen in water and
the biological activity of microorganisms in the soil which consumes oxygen.
The amount of oxygen in the soil varies according to how often and for how
long tides cover the mud, how well drained the areas are, and whether there
are chemicals in the soil that absorb oxygen. Oxygen in the soil could be
expected to increase in proportion to the amount of time that the soil is
exposed to the air and the soil is covered by water. Extreme lack of oxygen
in the soil can lead to the formation of gas, hydrogen sulphide, which has
rotten egg smell often associated with mangrove swamps.
The various functional types of
mangrove forest
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Over wash mangrove forests : exist as islands frequently washed over by
tides. All species are present with the Red mangrove the dominant species.
Typically, these islands develop as a Red mangrove propagule strands in a
shallow flat. As the island develops the roots eventually trap sediment.
Often, bare sand flats are found in the center of these islandsThe maximum
height of the community is between 7 m. These are small islands covered
with mangroves that are frequently washed by the tides. The dominant
species is Rhizophora mangle or the red mangrove.
Fringing mangrove forests : exist as a relatively thin fringe along
waterways. These forests appear to be flushed daily by tides, but do not
receive then amount of terrestrial runoff as the riverine forests. Typically, the
classic mangrove zonation pattern of seaward Red-Black-landward White
scheme is exhibited in this forest. Maximum heights of trees in this
community are slightly over l0 m. These strips of mangrove found along
waterways and covered by daily tides. The dominant species is Rhizophora
mangle.
The various functional types of
mangrove forest
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Riverine mangrove forests : are tall flood plain forests along flowing
waters such as tidal rivers and creeks. Conditions are favorable for
extensive growth due to flushing by daily tides. In addition, freshwater runoff
and terrestrial nutrient influx enhance this type of mangrove community.
Maximum heights of trees in this community are 66 feet (20 m). These are
luxuriant stands of mangrove along tidal rivers and creek with a good input
of fresh water. Often composed of Rhizophora, Avicennia.
Basin mangrove forests : are inland in depressions channeling terrestrial
runoff toward the coast. Trees in this community have maximum heights of
almost l5 m. These are stunted mangroves located in places such as the
interior of swamps. Often dominated by Avicennia.
Hammock mangrove forests : are in depressions but exist on slightly
elevated ground. Trees rarely growth height in excess of 5 m. Tidal flushing
of both of the communities is infrequent. Similar to basin mangrove forests
but are found in more elevated sites.
Scrub mangrove forest : are common in the flat coastal fringe of southern
Florida and the Keys. All 3 species are present, but height is limited to less
than l.5-2 m except in depressions of mangrove peat. Nutrients appear to
be the limiting factors affecting growth, although substrate (marl) is also
important. A dwarfed stand of mangroves found on flat coastal fringes.
Mangrove animal
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The mangrove forest is transitional between land and sea, the
animals that live there can come from either environment.
The mangrove animals live in a variety of habitats which can range
from within or on the surface of the mud, through the creeks,
channels and pools, to the tree roots, trunk and canopy.
The tidal cycle exercises a profound influence over the behavior and
activity of marine animals in the mangrove.
Large mangrove animals living on the surface of the mud, which is
exposed at low tides, are almost always protected from drying out
by a shell or some hard supporting structure.
Fishes, shell fishes and
crustaceans :
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Major constituents of this group in the mangrove environment of species of
fishes, species of shell fished and species of crustaceans.
Commercially important are Meretrix sp., Crassostrea sp., Penaeus sp.,
Scylla serrata and Mugil cephalis
Many crustaceans in the mangroves make burrows which are used for
refuge, the feeding, as a source of water or for establishing a territory
necessary for mating.
Some may filter water through their burrows, feeding on suspended detritus
and plankton while others may breed there. These burrows play and
important role in the mangroves, aerating, draining and turning the dense
waterlogged soil - a direct benefit to the plants which in turn give them
shelter.
There is a limit to how many burrows can be dug in any one area. It seems
that when there are too many, homeless crabs may try to take over
occupied ones. Some fiddler crabs and ghost crabs have been observed
filing in the burrows of their neighbors to maintain their territories
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Scylla serrata, the large edible swimming crab, inhabits the muddy bottom
of mangrove estuaries, as well as coastal brackish water.
Thalassina anomala, the mud lobster is also found along estuaries and tidal
rivers. They build long tunneling burrows that can reach up to four meters
in length and can be recognized by spectacular turrets of earth rising to two
meters in height above the surface.
Mud skippers are one of the fish which live on the mud flats associated with
mangroves shores. The mud skipper is a fish well adapted to alternating
period of exposure to air and submersion and is frequently seen hopping
along the mud at the water's edge. They are well-comouflaged and able to
change colour to match their background. It respires under water like other
fish but out of the water gulp air. When submerged it swims like a fish but
on land proceeds by a series of skips. Some of them can even climb trees
using their fused pelvic (rear) fins as suckers and their pectoral fins as
grasping 'arms'. When a mud skippers is out of water it carries in its
expanded gill chamber a reserve from which to extract oxygen. After a few
minutes, when this reserve is exhausted, it is replenished from pool or from
water in the burrows which they dig. The mud skipper's most noticeable
feature is a pair of highly mobile eyes perched on top of the head
to increase the field of view and to enable it to see both under and over the
water.
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Birds are a prominent part of most mangrove forests and they are often
present in large numbers. The mangrove habitats offer rich feeding
grounds for many of the large and more spectacular species as well as
a multitude of small birds. About 177 species of resident and migratory
birds are found in the mangrove forests. The most common among these
are Kingfishers, herons, storks, sea eagles, kites, sand pipers, Curlews,
terens etc. Flamingoes flock the exposed mud flats, during the low tides.
They use mangrove environs as breeding and feeding grounds.
A great deal of wildlife diversity is found in the mangrove forests of India.
The Royal Bengal Tiger is one of the unique resident species of mangroves
of the Sunderbans. Reptiles are also common in mangroves and
can include snakes, turtles, crocodiles and alligators. The salt water
crocodile, commonly found in mangroves, has adapted so well to salt water
conditions that it can survive indefinitely in a range of salinity's and appear
to have functional salt glands on its tongue. Monitor lizard (Varanus sp.),
estuarine crocodile, various species of monkeys, otters, deer's, fishing cats
and wild pigs are some of the most common species of mangrove
forests of India.