1998 United Nations Year of the Oceans

Sustainable Oceans and Coastal Zones
Program in Global Sustainability
University of California Irvine 92697-7070

Folke, C. et al. 1994. The costs of eutrophication from salmon farming: implications for policy. Journal of Environmental Management 40: 173-182.

Primavera, J. 1993. A critical review of shrimp pond culture in the Philippines. Reviews in Fisheries Science 1: 151-201.

Primavera, J. 1998. Socio-economic impacts of shrimp culture. Aquaculture Research 28, in press.

What's New?

New Scientific Journal: Mangroves and Salt Marshes

To Read

Ramsar Convention on Wetlands
The Run-up to the Conference of Parties to the Ramsar Convention on Wertlands, Costa Rica, 10-18 May 1999

If You're Turned on by Mangroves, Order This!

Kjerfve, B. et al. 1997. Mangrove Ecosystem Studies in Latin America and Africa. UNESCO and US Forest Service. From: USDA Forest Service, Southern Forest Experiment Station, Institute of Tropical Forestry, Call Box 25000, Rio Piedras, Puerto Rico, USA 00928-2500.

AIMS/IBM Project Home Page
WWW Sites of Interest to Ecologists
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Mangroves and Shrimp
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Sierra Club of Canada 1997
University of Rhode Island Coastal Resources Center
Watershed Awareness Program
Western Australian Mangrove Page
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WetNet- The Wetlands Network
WHSRN INDEX

Graham, A. 1997. Diversification of Gulf/Caribbean mangrove communities through Cenozic time.

    It is only in the last 20 years has the world begun to value wetlands for their natural assets to society. Up until recently, mangrove and marsh lands were considered murky, dark "wastelands" that were hazards to society, not beneficial in any way. For example, in 1951 Florida newspapers reported "300 homes blackened" and "two men killed" by "mangrove root gas" in Miami (Miami Herald, 15 November 1951, and the Miami News, 28 July 1961). Wetlands were used until recently as acceptable disposal sites for the most contaminated types of refuse and industrial chemicals. As such, vast areas of mangroves cut, wetlands drained and converted to dry land. As late as 1969, a short-statured mangrove forest in south Florida was considered, "..a form of wasteland" (Lugo and Snedaker 1974). Until the early 1970's the USDA's Soil Soil Conservation Service considered mangroves only for its "..relative suitability for crops, pastures, woodland, wildlife, or other uses..."

    For centuries in tropical countries mangroves were valued for not only their timber but also for their food production and soil stabilization values. In Southeast Asia, traditional mangrove agroforestry was conducted, using the indigenous knowledge that these plants could stabilize dikes, pond banks, and transportation pathways (Lugo and Snedaker 1974). But as populations grew, mangroves began to be looked upon more as a vast timber resource to be exploited. Massive deforestation of mangrove forests of coastal Asia resulted. Macne (1968) has beautiful black and white photos of forests of Rhizophora mucronata with trunks "30-40 cm in diameter and trees ca. 35 m tall", taken "south of Ranong, Thailand". All of these forests are now gone.

    Today, mangrove ecosystems are valued not only for their resource (timber) value but for their "ecosystem services" in soil building, watershed stabilization, coastal protection, fish habitats and nurseries, and as habitats for organisms for rural villagers to glean vital (and "free") protein resources. When valuation of all of the ecosystem services mangroves provide is accomplished, the forest left standing is more valuable than its timber alone. In Bintuni Bay, Indonesia, the intact mangrove forest is worth US$ 4,800 per hectare, while the timber is worth just US$ 3,600 per hectare. Not cutting the forest gives local people there $10 million a year in services, and protects fisheries worth $25 million a year (Ruitenbeek 1992).

The Mangrove Forest

    Mangrove ecosystems are the dominant ecosystems along sheltered tropical coasts, oftentimes comprising the "ecotone" between the coast and tropical rainforests. The mangrove ecosystem is defined as the complex plant community below the high tide level, typically found on flat coastal land in areas of high, year-round rainfall. mangroves are recognized by their characteristic presence of prop roots, pneumatophores, and viviporous seeds. They are one of the world's most productive ecosystems in terms of gross primary production and production of leaf litter.

Global Area of Different Forest Types

Forest Types	Area   (million sq. km)
Temperate Needle-Leaf Forests	13.9
Tropical Moist Forests	11.2
Temperate Broadleaf/Mixed Forests	7.2
Tropical Dry Forests	0.8
Mangrove Forests	0.2

Top Eight Nations with Remaining Mangrove Forests

Nation	Sq km (% World Total)
Indonesia	42,550 (23.5)
Brazil	13,400 (7.3)
Australia	11,500 (6.3)
Nigeria	10,515 (5.8)
Cuba	7,848 (4.3)
India	6,700 (3.7)
Malaysia	6,424 (3.5)
Bangladesh	5,767 (3.2)
Others	76,697 (42.3)

    Odum (1969) has described the mangrove ecosystem as a "pass through" type of system because of the large flow of organic matter transported through the mangroves to coastal zones by physical activities of tides, runoff and rainfall, and the intense biological activities of decomposition, uptake, and bioturbation occurring in the mangroves that are important "downstream" in the marine ecosystem. Snedaker (1978) has noted that mangrove forests differ from terrestrial ones in that the primary source of nutrients lies outside of the forests themselves, and nutrients falling as leaf litter are removed from the forest.

    However, the exact role of the mangroves in exporting nutrients and as a "pass through" environment is very site specific, depending very much on the local geomorphology and tidal regimes (Robertson and Alongi 1992).

    There are 12 genera belonging to 8 families of salt-tolerant mangroves (halophytic):

Avicennia; Suaeda; Laguncularia; Lumnitzera; Conocarpus; Xylocarpus; Aegiceras; Aegialitis; Rhizophora; Bruguiera; Ceriops; Sonneratia. A total of 36 species of mangroves exist around the West Pacific and Indian Oceans. There are less than 10 species in the West Africa-America region. Aegialitis has salt glands in the epidermal layer of the leaves to remove salt actively; other genera prevent salt from entering (Laguncularia; Rhizophora; Sonneratia).

    Compared with tropical rainforests the level of species diversity is low. In addition, the generation time of the species is long, upwards of 25-40 years.
 

the Rhizophora species, which has a membrane in its roots that excludes salt, allowing water to enter but not salt;
the Avicennia species, that allow salt to enter the xylem and pass through the leaf stomata in transpiration, with the salt then crystallizing on leaf surfaces.

    Each mangrove species has an optimal salinity distribution. Mangrove respiration rates have been found to be related to salinity, so that each species has been found to minimize its salinity-induced respiration rates. At salinities higher than optimal, respiration rates increase, decreasing net growth, production and leaf litter production. As a result, each mangrove species occupies a salinity zone to which it is best adapted, a dynamic adaptation been called the metabolic basis of zonation (Snedaker 1978).

    The are two types of mangrove communities: fringe mangroves and riverine mangroves. The fringe communities are found right along the coast, while riverine mangroves are found in environments characterized by a larger and more continuous supplies of fresh water are available (Lugo and Snedaker 1974). The structural development, reproductive capacity, and production of mangroves is inversely related to the availability of fresh water, e.g. tall, robust forests with high leaf litter production are present where fresh water availability is good, whereas stunted forests with smaller stem diameters and lower litter production are present where the availability of fresh water is limited (Medina and Francisco 1997).

    The principal determinants of mangrove production are:

   Tidal factors

transport of oxygen to the root system
physical exchange of the soil-water solution with the overlying water mass that removes toxic sulfides and reduces   the total salt content of the soil water.
  tidal flushing which determines the rate of sediment deposition or erosion
  vertical motion of the ground water table may transport nutrients regenerated by detrital food chains in to the mangrove root zones.

   Water Chemistry Factors

total salt content which governs the osmotic pressure gradient between the soil solution and the plant's vascular system, affecting the transpiration rate of the leaves.
high macro-nutrient content of the soil enables the maintenance of high production despite low transpiration rates caused by high salinity
allochthonous macro-nutrients in runoff dominates the mactro-nutrient budgets.

The Detrital Ecology of Mangrove Ecosystems
 
    Mangrove ecosystems are important, "transformative interfaces" between land and sea. The mangrove ecosystem imports inorganic matter from terrestrial systems and exports organic matter as "detritus" (both dissolved and particulate organic matter) to marine ecosystems. ("detritus" is a term coined by Odum and de la Cruz (1963) as "all types of biogenetic (sic) material in various stages of microbial decomposition").

    Mangroves litter production has been measured at 896 grams dry wt./m²/year (Lugo and Snedaker 1974), adding 224 g C/m²/year to the soils and waters. Mangrove laves are usually colonized by fungi such as Phycomycetes, bacteria and nematodes, etc. upon deposition into water Mangrove leaf litter provides the most important nutrient base for food webs leading to commercially important fisheries. The leaves themselves are poor in nutrients when they fall from the tress but once in the aquatic ecosystem the organic matter is transformed by bacterial decomposition into nutrient-rich, high protein detritus (Odum 1971).

    The C/N ratio of plants and other materials is a good measure of nutritional values to animals (Russell-Hunter 1970). Animals need a daily dietary amount of protein of about 16.5% of the dry weight of their diets, or a C/N ratio of 17:1; at ratios above 17:1 there is a dietary protein deficiency.

    Upon entry to water, heterotrophic bacteria and fungi degrade the leaf matter and soluble carbon released from the leaves, forming fungal/bacterial/organic flocs. Flocculation increases with increased salinity. Fungi are thought to cause the major amount of decomposition by producing external enzymes and producing hyphae to penetrate the leaves, whereas bacteria crowd the surface of particles (Fell and Master 1980).

    In conclusion, mangrove leaf litter is one of the most important food sources for nearshore tropical marine ecosystems due to its:

  Roles in nearshore, detrital food webs (Odum et al. 1973);
  Nutritional value for marine organisms (Fell and Master 1980); and
  Value to commercial fisheries (Macnae 1974; Martosubroto and Naamin 1977; Turner 1977).

The Ecology of Soils and Sediments in Mangrove Ecosystems

    Mangrove ecosystems are characterized by soils that are unconsolidated; waterlogged, saline soils with the consistency of a thick layer of organic ooze which is anaerobic just below the sediment surface. Anaerobiosis has a profound effect on the chemistry of important elements like nitrogen and phosphorus.
 

    Mangrove sediments rarely have a redox potential of greater than +100 mV; therefore, most of the iron is present as Fe⁺⁺ (ferrous ion iron) and soils are devoid of nitrate. Ferrous iron is soluble (and ferric is insoluble). As a result, most of the phosphorus in mangrove soils is soluble iron or calcium phosphates (where the sediment contains lots of calcium carbonates and the pH is greater than 7.5). Mangrove soils, however, have a limited availability to readily adsorb this phosphorus because they are already enriched with organic phosphorus and lack an adequate number of "exchange sites". Ammonium is the most prevalent form of nitrogen in these soils, and is found mainly in the interstitial waters, but porewater nutrient levels are low (in micromolar concentrations, Alongi and Sasekumar 1992). Low nutrient levels have been explained by the high uptake rates by the mangroves, and by bacterial uptake. Denitrification has been shown to reduce the levels to nitrogen in mangrove soils to low levels.

    Avicennia leaves have a high N concentration likely due to the fact that they accumulate glycinbetaine, a quartenary ammonium compound. Average total leaf N and P concentrations showed a tendency to be higher in riverine mangroves, suggesting an inverse relationship between salinity and nutrient availability (Medina and Francisco 1997).

    Feller (1995) has shown however that mangroves growing on calcareous substrates show P deficiency that limits growth and development.

    Mangroves deal with this very harsh environment by transporting oxygen to their roots. Mangroves have amazing structures called pneumatophores, along with knee and stilt roots that allow oxygen to be transported to their roots. As a result, sediments around their roots are oxidized and highly productive. Anaerobic conditions, however, are stressful for mangroves. It has been shown that anerobiosis is a major factor controlling plant growth. The energy costs for self-maintenance (as measured by the amount of respiration over gross primary production) rise as the soils become more anaerobic and as the salinity of waters increase.

Mangrove Ecology References

Alongi, D. and A. Sasekumar. 1992. Benthic communities, p. 137-171. In: Robertson, A. and D. Alongi, Editors. 1992. Tropical Mangrove Ecosystems. American Geophysical Union, Washington, DC.

Fell, J. and I. Master 1980. Fungi associated with the decomposition of the black rush in south Florida. Mycologia 71: 322-342.

Feller, I. 1995. Effects of nutrient enrichment on growth and herbivory of dwarf red mangrove (Rhizophora mangle). Ecological Monographs 65: 477-505.

Linden, O. and A. Jernelov. 1980. The mangrove swamp- an ecosystem in danger. Ambio 9(2): 81-88.

Lugo, A. and S. Snedaker. 1974. The ecology of mangroves. Ann. Rev. Ecol. System. 5: 39-64.

Macne, W. 1968. A general account of the fauna and flora of mangrove swamps and forests in the Indo-West-Pafici region. Advances in Marine Biology 6: 73-270.

Macnae, W. 1974. Mangrove forests and fisheries. FAO/UNDP Indian Ocean Fishery Programme, Report IOFC/Dev/74/34.

Martosubroto, P. and N. Naamin. 1977. Relationship between tidal forests and commercial shrimp production in Indonesia. Marine Res. Indonesia 18: 81-86.

Medina, E. and M. Francisco. 1997. Osmolality and 13C of leaf tissues of mangroves  from environments of contrasting rainfall and salinity. Estuarine, Coastal and Shelf Science 45: 337-344.

Odum, E. and A. de la Cruz. 1963. Detritus as a major component of ecosystems. AIBS Bulletin 13(3): 39-40.

Odum, W. 1971. Pathways of energy flow in a south Florida estuary. University of Miami Sea Grant Tech. Bull. 7: 162p.

Odum, W. and E. Heald. 1972. Trophic analyses of an estuarine mangrove community. Bull. Mar. Sci. 22(3): 67-738.

Odum, W. and E. Heald. 1975. Mangrove forests and aquatic productivity: In: A. Hasler (ed.) Coupling of land and water systems, p. 129-136. Ecological Studies No. 10. Springer-Verlag, NY.

Odum, W. et al. 1973. Importance of vascular plant detritus to estuaries, p. 91-114. In: proceedings of the Symposium on Coastal marsh and Estuary Mgt. LSU, Division Continuing Education, Baton Rouge, LA.

Parnas, H. 1975. Model for decomposition of organic material by microorganisms. Soil Biol. Biochem. 7: 161-169.

Robertson, A. and D. Alongi, Editors. 1992. Tropical Mangrove Ecosystems. American Geophysical Union, Washington, DC.

Russell-Hunter, W. 1970. Aquatic productivity. Macmillan, New York.

Snedaker, S. 1978. Mangroves:their value and perpetuation. Nature and Resources 14(3): 6-13.

Teas, H. 1983. Biology and ecology of mangroves. Junk Publishers, The Hague.

Turner, R. 1977. Intertidal vegetation and commercial yields of penaeid shrimp. Trans. Am. Fish. Soc. 106: 411-416.

1. Uncontrolled Population Growth

    Demands for resources (food, water and energy,etc.) are driven by the addition of nearly 90 million persons a year to the Earth. Add to this unparalleled rise in the numbers of people on Earth is the unprecedented growth in affluence in East Asia. Population growth is tied to urbanization, ecosystem destruction, food, water, energy, health, public safety and community stability issues. Curbing population growth is the key issue for future environmental and social sustainability of the mangrove ecosystem and the peoples who depend upon them for survival.

    In the USA, the net increase of 3 million persons per year is blamed from the loss of million of acres of farmland to urbanization and lack of water. 60% of the US population growth is caused by foreign immigration, a portion that will rise to 90% in coming decades if current immigration policies continue (Pimental 1997).

    In developing nations, the population/food nexus is even more alarming. Over the next 20 years, of every 10,000 new births, only 50 will be in the rich countries (Swaminathan 1992). "A poverty curtain divides the world materially and philosophically. One world is literate, the other largely illiterate; one industrial and urban, the other predominately agrarian and rural; one consumption oriented, and the other struggling for survival" (Swaminathan 1992). The rich countries today consume about 20 times more resources per capita than the poor countries. But as economies have strengthened, especially in Southeast Asia, consumption rates of resources are rising dramatically.

    Recently, a group of scientists have banded together to ask world leaders to provide leadership to initiate incentives to reduce family size and conserve natural resources in order to maintain an ethical and decent standard of living (Pimental and Dodds 1997)

    Until very recently in many countries, mangroves were considered wasteland. Mangroves are still considered as such in many economically developing countries rapidly developing their coastal lands (as Europe and America did before them; for example, most of the mangroves have been destroyed for housing, roads, harbors in the Tampa and Biscayne Bays of Florida, USA).

    In earlier times, mangroves were valuable as sturdy poles in Arabian towns, where they idea of the "skyscraper" was born. States Macane (1968), "Much of downtown Singapore is built on piles of mangrove trees, chiefly rhizophoras". In earlier days in Southeast Asia, and today in many areas of coastal Africa, South Asia, and Latin America, mangrove are still cut for firewood and charcoal. Macnae (1968) state that "the extensive estuarine forests near Suratthani in peninsular Thailand have been "virtually exterminated" for this purpose.

    The rapid expansion of coastal cities throughout the world is exerting major impacts on all coastal ecosystems. There is a massive amount of rural to urban migration occurring in the developing nations. Most of this movement is from inland rural areas to coastal areas. The population of Calcutta, India increases about 1,000 persons a day due to this type of migration. China's Vice Minister of Construction just announced that it hopes to build 600 new cities by 2010, doubling the 633 already in existence (Gardner 1997).

    Rapid urbanization of the coastal zone threatens the livelihoods of all remaining peoples dependent on mangroves for their livelihoods. In Bangladesh, it has been estimated that one-third of the population is dependent on mangroves for their income (UNESCO 1979). Extensive destruction of the mangrove coasts of south and southeast Asia may be one of the reasons for the repeated catastrophic floodings and damage by storms reported in the past decade.

    There are also reports of extensive mangrove destruction caused by oil pollution, herbicides, and by war.

    Coastal aquaculture development (fish and shrimp ponds) has caused a further reduction in mangrove areas in Asia and the Americas. The extent of destruction due to aquaculture is, however, unclear. What is clear is that this new, coastal aquaculture development has accelerated the loss of this extremely important habitat in many countries.

    Primavera (1991) estimates that Philippine mangroves have declined from 400,000-500,000 ha in the 1920s to 140,000 ha, with 60% of the destruction due to coastal aquaculture of milkfish and shrimp.

    Larsson et al. (1994) reports that there is no evidence that mangroves have been cut down for aquaculture development in Columbia.

    Binh et al. (1997) reported that from 1983-91 one district of Vietnam (the Ngoc Hien district) lost 48% of its mangroves to shrimp pond development.

1. all shrimp ponds were to be located 50 m behind the mangroves,
2. no alteration of mangrove cover would be allowed,
3. no alternation of natural water flows by dams, walls, or diversions,
4. traditional uses and access to mangrove areas would be guaranteed to the local peoples,
5. ecotourism activities and research were to be encouraged.

    There has been some studies of reclaiming abandoned shrimp ponds, but the abandoned environment has been found to present many challenges due to salinization, nutrification, and deposits of residues from unsustainable farming parctices (Stevenson and Burbridge 1997).

Use of abandoned shrimp ponds in Samat Sakorn, Thailand

Conversion Use	Area in ha (%)
To low intensity shrimp culture	1,173 (33)
To Salt Farming	711 (20)
To Coconut Plantations	248 (7)
Soil Sold for Construction	248 (7)
Idle or Unidentified	1,175 (33)

From: Stevenson and Burbridge (1997)

Chan, H.T. 1991. The need to develop a management scheme for mangrove forests in South Jahore to ensure resource sustenance, p. 311-315. In; L.M. Chou et al. (eds.) Towards an inegrated management of tropical coastal resources. ICLARM, Manila, Philippines.

Chua, T.-E. 1993. Coastal aquaculture development and the environment. The role of coastal area management. Marine Policy 25: 98-103.

DeFur, P. and D. Rader. 1995. Aquaculture in estuaries: feast or famine? Estuaries 18: 2-9.

Dierberg, F. and W. Kiattisimkul. 1996. Issues, impacts, and implications of shrimp aquaculture in Thailand. Environmental Management 20: 649-666.

Kjerfve, Lacerda & Diop, editors. 1997. Mangrove ecosystem studies in Latin America and Africa. UNESCO. Forest Service, USDA, IITA, PO Box 25000, Rio Piedras, PR 00928-6302.

Ochoa, E. 1997. Majagual: the tallest mangroves in the World. Intercoast Special Mangrove Edition #1, March 1997: 17.
 

1. Value to Fisheries

   Mangrove swamps serve as vital nursery grounds for the economically important nearshore species such as snappers (Lutjanidae), jacks (Carangidae) and mullets (Mugilidae). Snedaker (1978) estimated that upwards of 90% of nearshore marine species were found in the mangroves during one or more parts of their life cycles. The success of nearshore fisheries in many tropical regions depends as much on the mangrove habitats themselves rather than the detrital foods for recruitment success.  Robertson and Blaber (1992) found that from 26-197 fish species were reported to use mangrove habitats in the Indo-west Pacific and tropical Atlantic.

    However, even though much research has been done, Robertson and Blaber (192) state, "..the role of mangroves in estuarine dependence by fish remains to be clarified". The three main hypotheses to explain the high densities of fish species and biomass in mangroves are:

turbidity reduces the effectiveness of large predators,
mangroves are important feeding sites for fish,
the structural complexity and increased living space gives shelter from predators.

States Robertson and Blaber (1992), "These three hypotheses...are probably all important in explaining the importance of mangrove habitats to fish. The relative significance of each hypothesis...will vary depending upon the fishes in question and the particular nature of each mangrove habitat."

2. Shoreline Protection

    Because of the high sedimentation rates in the mangroves, they build land. As such, they are an important "pioneer" species extending into the coastal zone, and connecting the marine ecosystems to the edge of the rain forest. Indeed, removal of mangroves has been blamed for the increased erosion and severity of storm impacts in  Bangladesh and other areas of the world. Mangroves have been used for years to protect seaward facing areas from erosion, also for protecting causeways, railroads and embankments in Florida, Hawaii, Sri Lanka, and traditionally in Southeast Asia.

    Mangroves have been used for centuries to stabilize the ponds of traditional marine aquaculture ponds in Java (Macnae 1968).

3. Habitat

    There are a variety of habitats in the mangroves:

the forest canopy. This is essential a terrestrial environment rich in epiphytes, orchids, and resembles a rain forest with high diversity. Many species of birds are found nesting and caring for young.
the soil. Some organisms move away from seawater and up mangrove trees upon inundation. Others bury in soil when the tides rise. Large numbers of snails abound.
root holes and clefts. A freshwater environment with a large number of insect larvae.
permanent or semi-permanent pools. Contain a variety of shrimp, crabs, fish, snails and frogs normally found in the canals and river branches in the mangroves.
branches and aerial roots of mangroves. Dominated by filter feeders such as barnacles, sea squirts, oysters, mussels, etc. An extremely high biomass is present here (Lindestrom et al. 1979).

4. Valuation of Mangrove Ecosystems Services 

Dixon, J. 1989. Valuation of mangroves. Tropical Coastal Area Management 4(3): 1-6.

Primavera, J. 1998. Socio-economic impacts of shrimp culture. Aquaculture Research 28, in press.

Ruitenbeek, H. 1992. Mangrove management: an economic analysis of management options with a focus on Bintuni Bay, Irian Jaya, Indonesia. Environmental Reports No. 8. EMDI, Gabriola Island, Canada.

    Due to the well-know abilities of marshes and mangrove ecosystems to absorb nutrients and tolerate adverse environmental conditions, there is a great deal of interest in using wetland ecosystems worldwide to treat humanity's wastes. Mangrove ecosystems have been proposed as an alternative, low cost sewage treatement system (Nedwell 1975; Clough et al. 1983), and, more recently, as a possible repository of effluents and sediments from shrimp aquaculture (Rajendram and Kathiresan 1997).

    Mangroves grow in waterlogged, saline, anaerobic soils and have developed remarkable adaptations to deal with these conditions, such as oxyen-transporting prop roots, pneumatophores, and resistent, viviporous seeds. The strong anaerobic environment makes a unique nutrient regime, nitrate is almost absent and iron exists as Fe⁺⁺. The low pH and redox potentials lead to release of phosphate. There is evidence that these characteristics lead to some mangrove being nutrient limited by both N and P.

    When soluble P is added to mangrove soils it is rapidly adsorbed, increasing the exchangeable (or labile) phosphorus. However, the capacity of mangrove soils to immobilize phosphorus is related to the number of available exchange sites, and these sites can be saturated. A lower adsorption maximum was found for mangrove soils that had received sewage effluent for 20 years (Clough et al. 1983). Holford and Patrick (1979) concluded that mangrove soils had a limited short-term capacity to reduce phosphorus in sewage effluent below that required for significant biological activity.

    Heavy metals are strongly bound to anaerobic sediments, either by adsorption, binding, or precipitation as insoluble sulfides. Pesticides are also strongly adsorbed onto mangrove sediments, especially those with high clay and humic acid contents.

    Shrimp pond and sewage effluents contain BOD's of 10-70 mg/liter. Clearly, these effluents will increase bacterial activities and increase the anaerobic nature of the sedimentary ecosystem. While mangroves are well adapted to anaerobiosis, there is evidence that anaerobic conditions are the major factor controlling plant growth. Additional organic inputs would inbcrease an already stressful situation for the plants, and decrease growth. However, addition of soluble nutrients could possibly help to ameiliorate nutrient stress in the mangroves (Clough et al. 1983). Rajendran and Kathiresan (1997) found that diluted (70%) shrimp pond effluent increased shoot biomass production, but that full strength effluent decreased biomass production.

      However, while mangrove ecosystems could serve as a trap for nutrients, pesticide or heavy metal-rich sediments, there could be an adverse effect on the mangrove food web and sediment fauna.

Bibliography

Clough, B. et al. 1983. Mangroves and sewage: a re-evaluation, p. 151-161. In: H. Teas (ed.) Biology and Ecology of mangroves. Dr. W. Junk Publishers, The Hague.

Holford, I. and W. patrick. 1979. Effects of redox potential and pH on phosphate removal from wastewater during land application. Progress Water Technology 11: 215-225.

Nedwell, D. 1975. Inorganic nitrogen metabolism in a eutrophicated tropical estuary. Water Research 9: 221-231.

Rajendran, N. and K. Kathiresan. 1997. Effect of effluent from a shrimp pond on shoot biomass of mangrove seedlings. Aquaculture Research 27: 745-747.

Coral Reefs and Mangroves
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Western Australian Mangrove Page
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