Forests at the Water's Edge
From the birds that roost in the leafy canopy to the crabs that scurry
about the trunks and the sponges and barnacles that live on submerged
"roots", it is easy to see that a variety of organisms call the
mangrove habitat home.
are trees that live at or near the water's edge in protected marine
habitats. This means that, while you are likely to find mangroves along
the calm banks of the IRL you won't find them on wave-beaten ocean shores.
There are several different types of
mangrove trees in the IRL, and they are not very closely related to one
another. So what makes a mangrove tree a mangrove tree?
There are several features that all species of mangrove trees have in
Tolerance to conditions of high soil salinity. Tolerance to submergence in
water or waterlogged soil, and to low oxygen conditions. Reproduction by
means of specialized seeds called "seedlings." Use of water to
disperse young plants.
In the middle of a mangrove clump (called a "mangle"), the
amount of salt in the soil can be up to three times the amount found in
ocean water. This concentration of salt is due to repeated flooding of the
soil, followed by evaporation of water, leaving the salt behind. Mangrove
trees are adapted to survive in salty soils that would kill most other
kinds of plants. This is one reason why mangrove trees can thrive in areas
too harsh for other vegetation. Some species, like the black mangrove (not
shown), actually get rid of excess salt by "sweating" it out of
Have you ever gone snorkeling before? If
you have, then you have something in common with the black mangrove tree.
Black mangroves survive in water- logged
soil by using special "root snorkels" called pneumatophores.
These structures are covered with small holes called lenticils that allow
the roots to breathe the same way a snorkel lets you breathe while
Use of Specialized Seeds
Most plants produce seeds which don't
sprout until they are planted. Mangrove seeds are different because they
actually start to grow into a new plant while they are still attached to
the parent tree. We call these specialized seeds seedlings. The picture
shows you what seedlings from a red mangrove tree look like.
reason mangroves use these special seedlings is that the head- start in
growth it gives young mangroves allows them to quickly take root when they
are deposited in a favorable growing area. Ordinary seeds would probably
be washed away before they have a chance to start growing.
Dispersal of Seedlings
Some plants, like dandelions, disperse their seeds by means of the wind.
Other plants, such as apple trees, rely on animals to help disperse their
seeds. Unlike these plants, the seedlings of mangrove trees are carried
away from the parent tree by water. The picture shows an underwater view
of several floating red mangrove seedlings.
If and when the tides or currents transport
the seedlings to an area suitable for growth, the young mangrove quickly
roots itself and begins the next stage of its life. Here, you can see
several newly arriving seedlings growing along with some slightly older
There are many plant and animal species which live within the mangrove
community and depend on this unique habitat for their continued existence.
Some, like the mangrove tree crab shown here, live upon the emergent (out
of water) portions of mangrove trees. Pelicans and other seabirds also
roost in the canopies of mangrove trees. Often, they form large rookeries
- nesting assemblages of adult birds and their offspring - during the
Other species, such as the young
mangrove snappers (2M) shown in this movie, spend the first years of
their lives living within the submerged tangle of mangrove roots. Here,
these fish find an abundance of food to eat, while remaining protected
from larger predators which inhabit more open waters.
portions of mangrove trees also provide living space for organisms which
require a hard surface on which to live. Mangrove trees are very important
in the IRL because there is very little hard bottom. The picture shows
some of the organisms commonly found on submerged mangrove roots,
including algae, sponges, sea squirts and barnacles.
Now that we have discussed the various features which all mangroves share,
let's take a closer look at the three most important mangrove species
which occur along the IRL - the red, black and white mangroves. Click on
each photograph to learn more about a particular species.