Background The programme of work on agricultural biodiversity, adopted by the Conference of Parties in decision V/5, makes provision for case studies on various topics to identify management practices, technologies and policies that promote the positive and mitigate the negative impacts of agriculture on biodiversity, and enhance productivity and the capacity to sustain livelihoods. More specifically, activity 2.1 of the Programme of Work calls for a series of case studies, in a range of environments and production systems, and in each region: (a) To identify key goods and services provided by agricultural biodiversity, needs for the conservation and sustainable use of components of this biological diversity in agricultural ecosystems, and threats to such diversity;

/pdf/convention-on-biological-diversity-3ne26rh5o6.pdf

Convention on Biological Diversity

SUMMARY Mangroves, the only woody halophytes living at the confluence of land and sea, have been heavily used traditionally for food, timber, fuel and medicine, and presently occupy about 181 000 km 2 of tropical and subtropical coastline. Over the past 50 years, approximately one-third of the world’s mangrove forests have been lost, but most data show very variable loss rates and there is considerable margin of error in most estimates. Mangroves are a valuable ecological and economic resource, being important nursery grounds and breeding sites for birds, fish, crustaceans, shellfish, reptiles and mammals; a renewable source of wood; accumulation sites for sediment, contaminants, carbon and nutrients; and offer protection against coastal erosion. The destruction of mangroves is usually positively related to human population density. Major reasons for destruction are urban development, aquaculture, mining and overexploitation for timber, fish, crustaceans and shellfish. Over the next 25 years, unrestricted clear felling, aquaculture, and overexploitation of fisheries will be the greatest threats, with lesser problems being alteration of hydrology, pollution and global warming. Loss of biodiversity is, and will continue to be, a severe problem as even pristine mangroves are species-poor compared with other tropical ecosystems. The future is not entirely bleak. The number of rehabilitation and restoration projects is increasing worldwide with some countries showing increases in mangrove area. The intensity of coastal aquaculture appears to have levelled off in some parts of the world. Some commercial projects and economic models indicate that mangroves can be used as a sustainable resource, especially for wood. The brightest note is that the rate of population growth is projected to slow during the next 50 years, with a gradual decline thereafter to the end of the century. Mangrove forests will continue to be exploited at current rates to 2025, unless they are seen as a valuable resource to be managed on a sustainable basis. After 2025, the future of mangroves will depend on technological and ecological advances

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0376892902000231

Present state and future of the world's mangrove forests

Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions.

Because of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules.

Mangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds).

Because they are surrounded by loose sediments, the submerged mangroves' roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character.

Living at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves.

Habitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged.

These impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests.

Mangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the world's most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

Biology of mangroves and mangrove Ecosystems

http://people.uncw.edu/pawlikj/2008AquatBotNagle.pdf

The habitat function of mangroves for terrestrial and marine fauna: a review

Organic carbon dynamics in mangrove ecosystems : a review

The density of the burrowing crab fauna in a mangrove forest was reduced, using pitfall traps, to test the hypothesis that decreased burrowing would lead to: (1) increased soil sulphide concentrations; (2) altered nutrient concentrations; and (3) decreased forest productivity and growth. Experiments were conducted in Rhizophora -dominated forests in north Queensland, Australia, over a 12-month period. Crabs were trapped and removed from the experimental plots during 1 week each month for a year. Soil chemical and forest growth parameters were measured at monthly intervals in the experimental and appropriate control plots. Over the course of the experiment, soil sulphide and ammonium concentrations increased to levels which were significantly higher in plots from which crabs were being removed in comparison to controls. No differences were observed for either phosphate or nitrate plus nitrite. Cumulative forest growth, as measured by stipule fall, was significantly less in removal plots than in controls. Additionally, trees in the removal plots had significantly less reproductive output than did trees in control plots. These results support the hypothesis that burrowing by crabs is an important process in Australian Rhizophora forests. It appears that burrowing affects soil aeration which in turn affects the productivity and reproductive output of Rhizophora . Knowledge of the ecology of grapsid crabs from other continents, however, is very limited. It remains to be seen if the roles played by grapsid crabs are as important elsewhere as in Australia. This is particularly true for the Caribbean region from which many of our paradigms concerning mangrove forest ecology were developed.

Keystone species and mangrove forest dynamics: the influence of burrowing by crabs on soil nutrient status and forest productivity

The results of a study of soil factors in relation to plant growth for a tropical mangrove forest in northern Australia are presented and discussed. Basic soil properties are described briefly in terms of particle size distribution, bulk density and total carbon, nitrogen and phosphorus. Soil redox potential, pH, salinity and extractable nitrogen and phosphorus were monitored monthly over a 14 month period commencing April 1979. Sampling was carried out at 9 sites along a 370 m transect which exhibits strong gradients in topography, above ground biomass, canopy height and species distribution. Statistical analysis of the data shows that above ground biomass correlates significantly with the following soil factors, averaged over depth within the rooting zone and over time: Extractable P (r=0.85, p<0.01), redox potential (r=0.89, p<0.01) and salinity (r=−0.79, p<0.05). The strong biomass-EH correlation may be partly due to oxygen translocation by the plants to the root zone. Soil ammonium levels were within the range of 1–14 μg N per g (dry wt) and, unlike the above parameters, showed only minor variation with position along the transect. Variation of ammonium levels with time was apparent, but no significant correlation with rate of new shoot growth could be demonstrated, although depth profiles indicated depletion of ammonium by plant uptake during rapid growth periods. In addition neither soil ammonium, extractable phosphorus nor rate of plant growth showed any definite seasonal periodicity in this tropical system.

Soil characteristics and nutrient status in a Northern Australian mangrove forest

Particulate carbon and nitrogen exports from a north Queensland mangrove system are estimated Mangrove litter, flushed by tidal action at a rate of 10 kg C ha −1 day −1 , represents the major component of organic matter export The net exchange of tidal-borne micro-particulate matter is difficult to estimate precisely However, the net export rate attributable to this component is approximately 1·5 kg C ha −1 day −1 The nature of the microparticulate matter is described with particular reference to the variation of total organic carbon, adenosine triphosphate (ATP) and chlorophyll during a tidal cycle

Kevin Boto

Papers

Keystone species and mangrove forest dynamics: the influence of burrowing by crabs on soil nutrient status and forest productivity

Soil characteristics and nutrient status in a Northern Australian mangrove forest

Tidal export of particulate organic matter from a Northern Australian mangrove system

Food Chains and Carbon Fluxes

Nitrogen and Phosphorus Cycles