ENY660

Mangroves1

Jorge R. Rey and C. Roxanne Connelly2

1. This document is ENY660, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date January 2002. Revised January 2006 and June 2015. Visit the EDIS website at http://edis.ifas.ufl.edu.

2. Jorge R. Rey, professor; and C. Roxanne Connelly, professor, Entomology and Nematology Department, Florida Medical Entomology Laboratory, UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.

IntroductionMangroves are mostly tropical trees or shrubs that grow between near mean sea level and the high spring tide mark in stable shores where they form distinct communities known as mangals or mangrove forests. True mangroves have a number of features that help them thrive in this boundary zone between land and ocean including adapta-tions for mechanical fixation in loose soil, breathing roots and air exchange devices, specialized dispersal mechanisms, and specialized mechanisms for dealing with excess salt concentrations. Mangroves are the only true viviparous plants. This means that the seed remains attached to the parent plant and germinates into a protruding embryo (propagule) before falling from the tree (Figure 1).

In general, mangroves can be characterized by the following attributes:

• Adaptations, such as specialized roots, that help them cope with their environment.

• The ability to exclude or filter out salt.

• Seeds germinate while still on the parent plant.

• Restricted to the mangrove environment.

• Taxonomic isolation (no close terrestrial relatives at least at the generic level).

Mangroves thrive in protected shores with fine grained sediments where the average temperature of the coldest month is greater than 20° C. Many factors influence mangrove development and zonation, including a number of edaphic (soil), hydrographic (water), chemical, geologi-cal, meteorological, biological, and stochastic (chance) components (see Tomlinson 1986, for detailed discussion of these factors).

ZonationThe existence of distinct zones, each dominated by differ-ent mangrove species is often evident in well developed mangals (Figure 2). Mangrove zonation, however, is more often manifested as a mosaic that varies with the complex of physical, chemical, and biological interactions occurring in a particular area. Because mangrove environments are so diverse, it is usually difficult to determine the general ecological requirements of different species, as detailed studies in one area may be contradicted by equally precise studies of the same species in a different area.

Figure 1. Red mangrove propagules: young (left) and mature (right).

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SuccessionThe subject of mangrove succession, the notion that at a given place there is an orderly replacement of vegetation with time from the first colonizers (pioneers) to a final, stable group (climax), has been studied and debated for many years but few consistent patterns and processes have emerged. One major problem is the absence of datable growth rings in most mangrove species, which makes it difficult to match current observed patterns in space with dynamic processes that have occurred over time. Further-more, as noted above, ecological requirements of many species are ambiguous, with studies of the same species in different regions often yielding conflicting results.

DiversityTomlinson (1986) lists 34 species belonging to 9 genera and 4 families as major components of the mangals worldwide, and 20 species from 11 genera and 10 families as minor components. Biogeographically, mangroves can be divided into two distinct groups: (1) the Indo-Pacific group, with approximately 40 species of true mangroves, includes East Africa, India, Southeast Asia, Australia, and the Western Pacific; (2) West Africa, the Caribbean, and the Americas with only 8 true mangrove species in the region. The greatest species diversity is found on the coasts of Malaysia, Indonesia, and New Guinea. Although extensive mangals

are only found in tropical and subtropical regions, some mangroves occur as far north as Kyushu Island, Japan (35° N), and as far south as Auckland, New Zealand (37° S).

Key to New World Mangroves1A. Leaves opposite, flowers small (1-1.5cm); aggregated aerial roots usually present - go to 2.

1B. Leaves alternate, flowers showy, large (10-12 cm); terminal aerial roots absent, trunk base expanded and fluted - Pelliciera.

2A. Stipules present, overwrapping, leaving a conspicuous ring-like scar above petiole insertion; flowers small (1cm), seedlings conspicuous, viviparous; aerial roots forming arching loops from trunks and branches - Rhizophora.

2B. Stipules absent; seedlings not conspicuously viviparous; aerial roots from underground cable roots - go to 3.

3A. Leaf undersurface with fine glaucous grey indumen-tum; leaf base grooved; petiole without glands aerial roots; as pointed pneumatophores - Avicennia.

3B. Leaf undersurface glabrous; petiole with a pair of glands just below insertion of blade; pneumatophores, if present, blunt, not pointed - Laguncularia.

Figure 2. Hypothetical mangrove zonation in Florida.3

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Some terms found in the key:

aerial root: A root structure that rises above ground, usually above water, to allow the plant to absorb air.

glabrous: Smooth; not rough, or hairy.

glaucous: Bluish white; covered or whitened with a very fine, powdery substance.

indumentum: A massing of fine hairs, glands, or prickles.

petiole: The stalk of a leaf that attaches to the stem (leafstalk).

pneumatophore: A specialized root in certain aquatic plants that performs respiratory functions.

stipule: An appendage at the base of a petiole, often appear-ing in pairs, one on each side.

terminal: Borne at the tip of an organ, farthest from the point of attachment.

viviparous: The seed remains attached to the parent plant and germinates into a protruding embryo (propagule) before falling from the tree.

Florida MangrovesThere are three species of true mangroves in Florida: the red mangrove (Rhizophora mangle, Figure 3), the black mangrove (Avicennia germinans, Figure 4), and the white mangrove (Laguncularia racemosa, Figure 5). The buttonwood (Conocarpus erectus, Figure 6) is not a true mangrove, but is often found associated with the above species in the higher-elevation areas.

Figure 3. Red mangrove, Rhizophora mangle.

Figure 4. Black mangrove, Avicennia germinans.

Figure 5. White mangrove, Laguncularia racemosa.

Figure 6. Buttonwood, Conocarpus erectus.

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ImportanceMangroves are renowned for their high productivity and, consequently, are extremely important to the nutrient budgets of adjoining estuaries and other coastal waters. Mangrove forests also serve as important nursery, feeding, and refuge areas for a wide variety of terrestrial and aquatic organisms including mammals, birds, reptiles, fish, and invertebrates. Some of these species are threatened or endangered (Odum et al. 1982; Table 1) and others are highly valued by sports and commercial fisheries, inshore and offshore.

ImpactsIn spite of their ecological importance, mangrove forests are under intense pressure from human activities. Protection of the world’s mangrove forests is one of the great environ-mental challenges of the coming decades. In many parts of the world mangrove forests are being destroyed and/or degraded at an alarming rate. Direct loss of mangrove habi-tat by conversion to agricultural and/or urban lands; clear cutting for timber, fuel wood, wood chips, pulp, fodder, and charcoal; impounding for mosquito control; destruction for fish and shellfish culture operations; and conversion to salt ponds have resulted in the loss of over half of the area once occupied by mangroves (AAAS 1995).

Significant damage and loss of mangrove habitat can also be attributed to pollution, including oil spills, pesticides, agricultural and military herbicides, and industrial chemi-cals. Additionally, contamination with human wastes is a severe problem in some parts of the world. Although these effects have been well documented, there is very little data on the extent of global mangrove losses due to chemical pollution or on the resulting degree of forest degradation of the remaining acreages.

Natural events, such as direct destruction by hurricane winds and secondary diebacks caused by overflooding and clogging of the plants “breathing” organs by sand and silt, and mortality due to prolonged exposure to low ambient temperatures can also result in significant damage to mangrove forests.

Further ReadingSources for entry into the mangrove literature and for general information on mangroves include Chapman (1977), FAO (1982), Reimold and Queen (1974), Teas (1984a, 1984b), and Tomlinson (1986).

Selected References

AAAS. 1995. Proc. Human Population and Water, Fisher-ies, and Coastal Areas: Science and Policy Issues Symp., American Association for the Advancement of Science, Washington, D.C.

Chapman, V.J. 1976. Mangrove Vegetation. J. Cramer, Germany.

Chapman, V.J. (ed.). 1977. Wet Coastal Ecosystems, Eco-systems of the World 1. Elsevier Scientific Publishing Co., Amsterdam, 428 pp.

F.A.O. 1982. Management and Utilization of Mangroves in Asia and the Pacific. Food and Agriculture Organization of the United Nations Environmental Paper #3, Rome, 160 pp.

Field, C.D. 1995. Journey Amongst Mangroves. Interna-tional Society of Mangrove Ecosystems, Okinawa, Japan, 140 pp.

Lugo, A. E., and S. C. Snedaker. 1974. The ecology of mangroves, Annual Review of Ecology and Systematics 5:39-64.

Morton, J. F. 1965. Can the red mangrove provide food, feed, and shelter? Econ. Bot. 19:113-123.

Odum, W. E., C. C. McIvor, and T. J. Smith. 1982. The ecology of the mangroves of South Florida: a community profile. U.S. Fish and Wildlife Service, OBS Publication FWS/OBS-81/24, Washington, D.C. 144pp.

Reimold, R.J. and W.H. Queen (eds.). 1974. Ecology of Halophytes, New York: Academic Press, Inc, 605 pp.

Table 1. Partial list of threatened or endangered species utilizing Florida mangroves.4

Endangered Threatened

American Crocodile American Alligator

Hawksbill Turtle Green Turtle

Ridley Sea Turtle Loggerhead Turtle

Florida Manatee

Brown Pelican

Key Deer

Florida Panther

Atlantic Salt Marsh Snake

Eastern Indigo Snake

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Rey, J. R. 1999. Mangroves. In: R. W. Fairbridge and D. E. Alexander (eds.), Encyclopedia of Environmental Sciences. Kluwer Academic Publishers, Dordrecht.

Rutzler, Klaus, and C. Ilka. 1996. Caribbean Mangrove Swamps. Scientific American, 274: 94 - 99.

Teas, H.J. (ed.). 1984a. Biology and Ecology of Mangroves. Dr. W. Junk Publishers, The Hague, 188 pp.

Teas, H.J. (ed.). 1984b. Physiology and Management of Mangroves. Dr. W. Junk Publishers, The Hague, 106 pp.

Tomlinson, P.B. 1986. The Botany of Mangroves. Cam-bridge University Press, London, 413 pp.

On the Web:

Bann, C. The Economic Valuation of Mangroves: A Manual for Researchers.

http://www.idrc.ca/uploads/user-S/10305674900acf30c.html

Quarto, A. The Mangrove Forest. MAP Working Paper.

Additional Notes3After Tomlinson (1986).

4After Odum et al. (1982) and http://myfwc.com/me-dia/1515251/threatened_endangered_species.pdf