Avicennia germinans
is characterized by its opposite leaves which are narrow and elliptical in
shape; often found encrusted with salt. Propagules are small (2-3 cm in
diameter) and bean-like, flattened in shape. The root system of Avicennia
germinans consists of long underground cable roots which produce
hundreds of thin, upright pneumatophores on the ground around the tree.
These structures have numerous pores which are thought to conduct oxygen
to the underground portion of the root system.
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
Avicennia germinans occurs
worldwide in coastal and estuarine areas of the tropics and subtropics to about
28 degrees in both the northern and southern hemispheres.
IRL Distribution:
In the Indian River Lagoon, it is a
common landscape feature to approximately 28 degrees North, around the vicinity
of Merritt Island, Florida. North of this location, there is a transition zone where
mangrove forests gradually give way to salt marshes. Frost stress north of the
transition zone prevents mangroves from becoming well established.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Little is known regarding typical age to
maturation in mangroves in south Florida, though it has been hypothesized that
maturation age for mangroves in south Florida is in some way linked to the
periodicity of hurricanes.
Abundance:
The black mangrove is considered
abundant to common in the Indian River Lagoon, as well as throughout much
of its range.
Locomotion:
Propagules of the black mangrove detach
from the parent tree upon ripening and may float in salt water for approximately
one year without rooting.
Reproduction:
It is widely believed that the flowers of
Avicennia germinans are pollinated by insects, principally bees. Black
mangroves exhibit cryptovivipary, in which the embryo emerges from the seed
coat, but remains in the fruit before abscission from the parent plant occurs.
The seedlings, or propagules, eventually fall from the parent plant and are
able, in the absence of suitable substrata, to float for an indefinite period in
salt water without rooting.
IV. PHYSICAL TOLERANCES
Temperature:
The range of A. germinans
generally matches the 20 °C isotherm in both the northern and southern
hemispheres, and is similar to the range of coral reefs. Frost stress beyond 28
degrees north and south latitudes prevents most mangroves from becoming well
established. Avicennia germinans, however, has a somewhat wider
temperature range than other species. When subjected to cold stress, mangrove
populations show differences in survival rate and amount of damage done per
plant based on their geographic points of origin.
Salinity:
As facultative halophytes, mangroves have
the ability to thrive in waterlogged soils which may have salinities ranging
from 0 - 90 ppt. Mangroves exhibit several different types of mechanisms for coping
with highly saline conditions. The black mangrove (Avicennia germinans)
and the white mangrove (Laguncularia racemosa) are able to take up
seawater through their roots, but they excrete excess salt through pores, or
salt glands, located on the surface of leaves. A different strategy is employed
by Rhizophora mangle, the red mangrove, which excludes the salt in
seawater at the root-substratum interface.
Other Physical Tolerances:
Mangroves can experience reducing conditions
conditions to at least -200 mV. One of the most visibly obvious adaptations to
anoxia are root adaptations. The black mangrove utilizes upright pneumatophores
which grow from the underground cable roots. These structures contain numerous
pores which are thought to conduct oxygen to the underground portion of the root
system. Fine lateral rootlets are able to accumulate in the substratum, and
produce most of the underlying peat on which mangrove swamps are built.
Adaptations to extremes in pH
have not been examined in the red mangrove, however, pH values between 5.3 and
7.8 have been reported.
V. COMMUNITY ECOLOGY
Trophic Mode:
Mangrove forests typically show a wide
range of productivity, depending on factors such as hydrological regimes,
nutrient supply, etc., and are considered to be vital sources of organic matter
for estuarine systems.
Competitors:
Ball (1980) suggested that competition
among the 3 mangrove species may be partially responsible for the zonation
observed in many mangrove areas. Direct consumers of mangrove propagules in
Florida include the spotted mangrove crab (Goniosis cruentata), the
mangrove land crab (Ucides cordatus), the coffee bean snail (Malapus
coffeus) and the ladder horn snail (Cerithidea scalariformis).
Consumers of mangrove leaves include the mangrove crab (Aratus pisonii),
the spotted mangrove crab (G. cruentata), the blue land crab (Cardisoma
guanhumi), and various types of insects. Wood boring isopods feed upon and
damage prop roots.
Habitat:
Propagules of A. germinans may
float for an indefinite period without taking root. They generally take root
upon coming to rest on a suitable substrate area consisting of sand, silt, mud
or clay which offers some protection from waves. Propagules may root even while
completely submerged; and mature trees, depending on type, tend not to be
sensitive to hydroperiod; they may remain submerged anywhere from several hours
to nearly permanently without showing adverse effects.
Associated Species:
Mangroves form intertidal forests in
which red mangrove prop roots, black mangrove pneumatophores, and their
associated peat banks serve as the dominant substrata for other
members of the mangrove community. Black mangroves (Avicennia germinans)
and white mangroves (Laguncularia racemosa) are usually found in
association with red mangroves. Segregation of the 3 species does occur,
however; with red mangroves typically occupying the lowest intertidal position.
Black and white mangroves occur at slightly higher tidal elevations.
VI. SPECIAL STATUS
Special Status:
Habitat structure
Notes on Special Status:
Mangrove communities support
populations of invertebrates, birds and juvenile fishes. Birds
utilize mangrove areas as important nesting habitat, while many species of
commercially or recreationally important fish species utilize mangrove habitat
as nursery grounds while juveniles.
Benefit in the IRL:
Mangrove forest ecosystems are vital as sources of energy and provide
nursery habitat for juvenile fish and invertebrates. They also provide roosting
and nesting habitat for wading birds. In addition, mangrove communities provide
a source for timber production and are important as buffers in decreasing storm
impacts along coastlines.
Economic Importance:
While black mangroves have little direct commercial importance, they support
invertebrate communities, and populations of juvenile fishes. They
additionally help buffer coastlines against the impacts of tropical storms and
hurricanes.
VII. BIBLIOGRAPHY
Ball, M.C. 1980. Patterns of Secondary Succession
in a Mangrove Forest of
Southern Florida. Oecologia 44:226-235.
Chale, F. 1996. Litter Production in an Avicennia
germinans (L.) Stearn Forest
in Guyana, South America. Hydrobiologia
330:47-53.
Carlton, J. 1974. An Ecological Survey of Selected
Mangrove Communities in
Florida. Master of Arts Thesis. Department
of Biology in the University of
South Florida.
Day, J., W. Conner, et al. 1987. The Productivity
and Composition of Mangrove
Forests, Laguna De Terminos, Mexico. Aquatic
Botany 27:267-284.
Ellison, A., and E. Farnsworth. 1996. Spatial and
Temporal Variability in Growth
of Rhizophora mangle Saplings on
Coral Cays: Links with Variation in
Insolation, Herbivory, and Local
Sedimentation Rate. Journal of Ecology
84:717-731.
Everitt, J.H., and F.W. Judd. 1989. Using Remote
Sensing Techniques to
Distinguish and Monitor Black Mangrove (Avicennia
germinans). Journal of
Coastal Research 5(4):737-745.
Ewa-Oboho, I.O., and N.J. Abby-Kalio. 1993.
Seasonal Variation and
Community Structure of Epibenthic Algae on
the Roots of the Mangrove
Rhizophora mangle at a Shallow
Tropical Estuary. Tropical Ecology
34(2):160-172.
Johnston, S.A. 1983. Preliminary Report on Avicennia
Germinans Communities
Located on Ile De Chien, (Dog Island),
Franklin County, Florida. Tropical
Ecology 24(1):13-18..
Lin, G., and L.L. Sternberg. 1992. Comparative
Study of Water Uptake and
Photosynthetic Gas Exchange Between Scrub
and Fringe Red Mangroves,
Rhizophora mangle L. Oecologia
90:399-403.
Lin, G., and L. Sternberg. 1993. Effects of
Salinity Fluctuation on Photosynthetic
Gas Exchange and Plant Growth of the Red
Mangrove (Rhizophora mangle
L.). Journal of Experimental Botany
44(258):9-16.
Lin, G., and L. Sternberg. 1995. Variation in
Propagule Mass and its Effect on
Carbon Assimilation and Seedling Growth of
Red Mangrove (Rhizophora
mangle) in Florida, USA. Journal of
Tropical Ecology 11:109-119.
Lopez-Portillo, J., and E. Ezcurra. 1985. Litter
Fall of Avicennia germinans L.
in a One-Year Cycle in a Mudflat at the
Laguna de Mecoacan, Tabasco,
Mexico. Biotropica 17(3):186-190.
McCoy, E.D., H.R. Mushinsky, et al. 1996. Mangrove
Damage Caused by
Hurricane Andrew on the Southwestern Coast
of Florida. Bulletin of Marine
Science 59(1):1-8.
McKee, K.L., and I.A. Mendelssohn. 1987. Root
Metabolism in the Black
Mangrove (Avicennia Germinans (L.):
Response to Hypoxia. Environmental
and Experimental Botany 27(2):147-156.
McKee, K.L. 1995. Seedling Recruitment Patterns in
a Belizean Mangrove
Forest: Effects of Establishment Ability and
Physico-Chemical Factors.
Oecologia 101:448-460.
McMillan, C., and C.L. Sherrod. 1986. The Chilling
Tolerance of Black
Mangrove, Avicennia Germinans, From
the Gulf of Mexico Coast of Texas,
Louisiana and Florida. Contributions in
Marine Science 29:9-16.
Mullin, S.J. 1995. Estuarine Fish Populations
Among Red Mangrove Prop Roots
of Small Overwash Islands. Wetlands
15(4):324-329.
Patterson, C.S., I.A. Mendelssohn, et al. 1993.
Growth and Survival of
Avicennia germinans Seedlings in a
Mangal/Salt Marsh Community in
Louisiana, U.S.A. Journal of Coastal
Research 9(3):801-810.
Pulver, T.R. 1976. Transplant Techniques for
Sapling Mangrove Trees,
Rhizophora mangle, Laguncularia racemosa
and Avicennia germinans,
in Florida. Florida Department of Natural
Resources, Marine Research
Laboratory, Number 22, 14 Pages.
Rey, J.R. 1994. Effects of Neighbors on Growth and
Mortality of Mangrove
Seedlings in Florida, U.S.A. Wetlands
14(4):308-315.
Ribi, G. 1982. Differential Colonization of Roots
of Rhizophora mangle by the
Wood Boring Isopod Sphaeroma terebrans as a
Mechanism to Increase
Root Density. Marine Ecology 3(1):13-19.
Savage, T. 1972. Florida Mangroves: A Review.
Florida Department of Natural
Resources, Marine Research Laboratory, St.
Petersburg, Florida. Leaflet
Series: Volume VII - Marine Plants. Part 2
(Vascular Plants) No.1, 15
Pages.
Schmalzer, P.A. 1995. Biodiversity of Saline and
Brackish Marshes of the Indian
River Lagoon: Historic and Current Patterns.
Bulletin of Marine Science
57(1):37-48.
Sessegolo, G.C., and P.C. Lana. 1991.
Decomposition of Rhizophora mangle,
Avicennia schaueriana and Laguncularia
racemosa Leaves in a Mangrove
of Paranagua Bay (Southeastern Brazil).
Botanica Marina 34:285-289.
Smith, S.M., and S.C. Snedaker. 1995a. Salinity
Responses in Two Populations
of Viviparous Rhizophora mangle L.
Seedlings. Biotropica 27(4):435-440.
Smith, S.M., and S.C. Snedaker. 1995b.
Developmental Responses of
Established Red Mangrove, Rhizophora
mangle L. Seedlings to Relative
Levels of Photosynthetically Active and
Ultraviolet Radiation. Florida Scientist
58:55-60.
Snedaker, S.C., J.A. Jimenez, et al. 1981.
Anomalous Aerial Roots in Avicennia
Germinans (L.) L. in Florida and Costa
Rica. Bulletin of Marine Science
31(2):467-470.
Snedaker, S.C., M.S. Brown, et al. 1992. Recovery
of a Mixed-Species
Mangrove Forest in South Florida Following
Canopy Removal. Journal of
Coastal Research 8(4):919-925.
Soto, R. 1988. Geometry, Biomass Allocation and
Leaf Life-Span of Avicennia
germinans L.(Avicenniacae) Along
a Salinity Gradient in Salinas,
Puntarenas, Costa Rica. Rev. Biol. Trop.
36(2A):309-323.
Tattar, T.A., E.J. Klekowski, et al. 1994. Dieback
and Mortality in Red
Mangrove, Rhizophora Mangle L. in
Southwest Puerto Rico. Aboricultural
Journal 18:419-429.
Thibodeau, F.R., and N.H. Nickerson. 1986.
Differential Oxidation of Mangrove
Substrate by Avicennia Germinans and Rhizophora
Mangle. Amer. J. Bot.
73(4):512-516.
Vaughan, T.W. 1910. The Geologic Work of Mangroves
in Southern Florida.
Smithsonian Miscellaneous Collections 52(UML
14,101):461-464.
Report by: K. Hill,
Smithsonian Marine Station
with thanks to Gary Raulerson, LSU and C. Feller, NMNH
Submit additional information, photos or comments to:
irl_webmaster@si.edu
Page last updated: July 25, 2001
