Palm Beach County Board of County Commissioners
Department of Environmental Resources Management
Mangroves
Functions and Values
Mangroves serve very important functions in the ecology of South Florida. Mangroves have a
high ecological role as nursery grounds and as a physical habitat for a wide variety of
vertebrates and invertebrates. They recycle nutrients and the nutrient mass balance of
estuarine ecosystems. Mangrove leaves, wood, roots, and detrital material provide essential
food chain resources, and provide habitat for many wildlife including mammals, birds, reptiles,
amphibians, and arthropods. Mangroves have a special ecological function for endangered
species, threatened species, and species of special concern. They also serve as storm buffers;
their roots stabilize shorelines and fine substrates, reducing potential turbidity and enhancing
water clarity. One of the greatest values of mangroves swamps in Florida is their aesthetic
appeal.
Geographical Distribution Factors
Four major factors limit the distribution of mangroves: climate, salt water, tidal fluctuation and
soil type. Mangroves are found in tropical and subtropical estuarine habitats. They rarely
tolerate temperatures below freezing; therefore occur in regions where the annual average
temperature is above 19 C (66 F). Mangroves can live in salt water and are able to keep the salt
content lower than the salt content in the soil. They accomplish this with several methods:
secreting salt through salt glands; secreting salt through their roots; thick leaves with a waxy
covering; facultative halophytes. Water fluctuations are important to mangrove forest
development because the tidal action carries mangrove propagules into upper portion of the
estuary.
RED MANGROVE
Rhizophora mangle
The red mangrove is often found seaward of the other species and grows in frequently flooded
areas. This species belongs to the family Rhizophoraceae and is very easy to identify. Red
mangroves have characteristic aerial roots, which originate downward from the trunk and
lower branches. These roots are an adaption to saltwater environment. The tree can take in
oxygen directly from the surrounding air. The roots also provide the tree additional support to
remain upright in the muddy substrate. The leaves are shiny, thick, leathery and dark green.
Red mangrove fruits germinate on the parent tree to form long, pencil shaped propagules
which act as seedlings. These seedlings are denominated viviparous. Flowering in spring and
summer, although it can occur throughout the year. Although usually shorter than other types,
the red mangrove tree may reach up to 50 feet in height.
BLACK MANGROVE
Avicennia germinans
Black mangroves are often found in close association with red mangroves and seem to grow in
the most salt-rich soils. The tree belongs to the family Avicenniaceae. On the ground around
the black mangroves one can find numerous pneumatophores which extend upwards above the
mud from the submerged root system. Pneumatophores are essentially the erect lateral
branches of an otherwise horizontal root system. They serve the same aerating purpose as the
prop roots of the red mangrove. The leaves of the black mangrove are narrow and oblong, dark
green above and silver-green underneath. The black mangrove can grow as tall as 60 feet.
WHITE MANGROVE
Laguncularia racemosa
White mangroves usually grow on higher land, landward of red and black mangroves. They are
often found in association with black mangroves. The white mangrove belongs to the family
Combretaceae. Contrary to the other two species, the white mangrove does not develop prop
roots or pneumatophores. The most identifyable characteristic of the white magrove are the
leaves. The leaves are thicker and more oval than those of the red and black mangrove, and
they are uniform pale green on both surfaces. On either side of the stem one can see two small
glands on each leaf. The white mangrove grows as a tree or shrub and can reach a height of 50
meters or more.