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U.S.V.I. Fact Sheet #28
The Importance of Mangroves
The mangrove ecosystem is a group of salt-
tolerant shrubs and trees that form coastal or
estuarine forests. The main characteristics used to
define the mangrove ecosystem are air and water
temperature (warm), type of substrate (silt/clay),
ability to provide protection from wave energy (from
major disturbances), presence of salt water, tidal
range, ocean currents and shallow sloping shores.
Globally, there are 110 recognized species of plants
classified as mangroves, belonging to 20 different
families. Within the Caribbean, however, there
are only four (4) types of mangroves that
belong to three families. In the Caribbean,
mangrove species are generally delineated
based on the moisture of the soil and how well
they have adapted to tolerating salt levels.
Mangrove trees found in the Caribbean are Red
Mangroves, Rhizophora mangle, Black
Mangroves, Avicennia germinans, White L
Mangroves, Laguncularia racemosa, and the Button
Mangrove or Buttonwood, Conocarpus erectus.
These trees are found in different zones within the
mangrove forest, depending on their ability to
tolerate salt concentrations. Red mangroves are
found in the areas closest to the water and are usually
permanently inundated with salt water. The next
shoreward species are the black mangroves. Black
mangroves are the most widely distributed species
within the mangrove forest since they can tolerate a
wide-range of salinity. They are followed by the
white mangrove, which grows in brackish to salty
mud and is only intermittently affected by tides. The
buttonwood mangrove is the least affected by tides
and is usually found on the landward side of the
mangrove forest. They are not limited to saline
environments and are sometimes found outside of the
Mangrove forests serve many purposes including,
providing habitat to many species, acting as nursery
grounds, as wave buffers, protecting coral reefs and
seagrass beds from sedimentation, and man-made
benefits of mangroves, as
well as their commercial
uses, have made mangrove
forests very important
ecosystems. Many diverse
species inhabit mangrove
forests, including fish, birds,
reptiles, amphibians, mollusks, crustaceans and many
other invertebrates. Algae, sponges, corals and
anemones can often be found attached to exposed
roots. Clams, sea snails and mussels can be found
hidden in the crevices. Crabs can also be found
inhabiting mangrove forests. Coastal birds, such as
pelicans, spoonbills and ospreys, use the mangrove
canopy for nesting, roosting and feeding.
Mangroves provide juvenile fish with refuge from
large predators because the exposed prop roots and
pneumatophores provide ample hiding places for fish
and plenty of food. Up to 80% of global fish catches
are directly or indirectly dependant on mangroves
Many local commercially important fish species use
mangroves as nurseries. The juveniles remain in the
mangrove habitat until they grow larger and are less
vulnerable to predators. They then move to more
open habitats, such as seagrass beds and coral reefs.
Studies on St. Thomas and St. Croix have shown that
shorelines along mangrove forests are very important
habitat for spiny lobster and other reef fish, such as
grunts and snappers.
Mangrove lagoons are sheltered areas, however
the structure of the trees enable them to withstand
rare heavy wave impacts and help to dissipate wave
action from severe storms. It is because of this
durability and protection that boats are often moored
in mangrove lagoons during the hurricane season.
Mangrove forests are also important for protecting
shorelines from tsunamis and other high wave events.
It was determined that, after the 2004 Boxing Day
tsunami in Asia, villages with mangrove forests intact
survived the waves with a lot less damage than
villages on open beaches.
Mangroves help prevent sediments from reaching
other critical marine habitats, such as coral reefs and
seagrass beds. The health of these habitats is
dependent in part on clear water, so that sunlight is
able to penetrate the water column.
The retention of sediments and nutrients by
mangroves helps to prevent sedimentation on the
coral reefs, which could lead to the smothering of
reefs and the growth of algae on the reef from
increased nutrients in the water. Seagrass beds are
also dependent on clear water and decreases in
turbidity and sedimentation by the filtering of
help promote their *"
health as well. The
mangrove forests - ...
will lead to an .. ,
increase in the ri.
amount of sediment "
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discharged into the
ocean, thereby decreasing the overall health of
adjacent offshore habitats.
The accumulation of sediment by the roots in
mangrove forests also helps build land mass. As the
new land stabilizes, mangroves move seaward
leaving the new land to be colonized by other plants.
WRITTEN BY CHRISTINE O' SULLIVAN IN 2005 THIS
PUBLICATION WAS PRODUCED WITH FUNDS FROM
SPORT FISH RESTORATION
FOR MORE INFORMATION CONTACT
DIVISION OF FISH AND WILDLIFE
6291 ESTATE NAZARETH, 101,
ST THOMAS, VI 00802
PHONE 340-775-6762 FAX 340-775-3972
45 MARS HILL, ST CROIX, VI 00840
PHONE 340-772-1955 FAX 340-772-3227
Mangrove forests have several commercial uses.
Mangroves are cut and burned to produce charcoal.
They are also used to fashion fish traps and boat
construction. They are used as harvesting areas for
fish, shrimp (Altona Lagoon), lobster, mussels and
other mollusks. However, the USVI has a "no net
loss" regulation, meaning there cannot be a loss of
mangroves within the territory and permits are
required to even prune mangroves.
Mangrove lagoons are highly valued for eco-
tourism ventures. Kayaking and sailing tours take
place in these areas, since they are calm and provide
a safe area for both novice and expert boaters. Also,
because of the huge diversity of marine organisms
found in mangrove lagoons, snorkelers may be able
to see species that they may not otherwise be able to
The main threat to mangroves throughout the
world is their over-exploitation by man. Globally,
unsustainable harvesting of mangrove trees for
charcoal and lumber can lead to a rapid decline in the
amount of mangrove forests present.
Development along the coastline often results in
the removal of mangroves by dredging for marinas or
filling for construction. This has damaging effects on
adjacent habitats, such as coral reefs and seagrass
beds, as well as on the fish and shellfish that rely
heavily on mangroves for the completion of their
different life stages.
The destruction of mangrove forests will decrease
biodiversity within these areas, increase coastal
erosion, storm impacts and decrease fisheries
production. It is therefore very important that
mangrove lagoons be protected and conservation
methods be implemented to ensure their continued
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