B. Oceans and their coastal margins - Mangrove swamps

Mangrove swamps

Development

Source: http://ian.umces.edu/imagelibrary/displayimage-search-0-7614.html

Mangrove swamps are coastal wetlands found in tropical and subtropical regions. They are characterized by halophytic (salt loving) trees, shrubs and other plants growing in brackish to saline tidal waters. These wetlands are often found in estuaries, where fresh water meets salt water and are infamous for their impenetrable maze of woody vegetation.

Mangrove trees dominate this wetland ecosystem due to their ability to survive in both salt and fresh water. Red Mangrove (Rhizophera mangle) is easily recognized by its distinctive arching roots. Black Mangrove (Avicennia sp.), which often grows more inland, has root projections called pneumatophores, which help to supply the plant with air in submerged soils. White Mangroves (Laguncularia racemosa) often grow even farther inland with no outstanding root structures.

A wide diversity of animals is found in mangrove swamps. Since these estuarine swamps are constantly replenished with nutrients transported by fresh water runoff from the land and flushed by the ebb and flow of the tides, they support a bursting population of bacteria and other decomposers and filter feeders. These ecosystems sustain billions of worms, protozoa, barnacles (Balanus spp.), oysters (Crassostrea spp.), and other invertebrates. These organisms in turn feed fish and shrimp, which support wading birds, pelicans, and the endangered Crocodile.

Source: https://www.epa.gov/wetlands/mangrove-swamps

Source: http://www.slideshare.net/luoyanjie/mangrove-30464575

Source: http://www.friendsofmangrove.org.my/index.cfm?&menuid=10

Environmental and economic value

Because of their sensitivity to the cold, mangroves are restricted to the tropics and subtropics. Mangrove forests are an ecosystem of incredible biological diversity comprising hundreds of algae, mollusk, crustacean, fish, insect, reptile, bird, and mammal species. Saltwater crocodiles, pelicans, egrets, spoonbills, flying foxes and monkeys are all residents of mangroves, just to name a few. The trees’ intricate network of roots provides a shelter for many oceanic and freshwater species, and the forest is a food source for many types of organisms as well. While certain species spend their entire life span in this ecosystem, numerous fish species use the shelter of the mangrove as a nursing ground before heading to the open ocean, to the extent that one third of all marine species were born and raised in mangrove forests around the world. As a result, the mangroves’ well being is central to the health of many more ecosystems.

In addition to the important biological functions they perform, mangroves also provide crucial ecosystem services to people. Because of their high capacity to recover from natural disasters, mangroves are particularly valuable in the face of increasingly frequent and violent tropical storms and hurricanes. By offering an obstacle to wind and waves, they significantly decrease the intensity of the storm while reducing its human and material toll. For example, a mangrove section of 30 trees per 0.01 hectare and with a width of 100 m can reduce the destructive force of a tsunami by up to 90%. Their roots also play in important role in trapping sediments and stabilizing shorelines facing increased erosion pressures.

Besides their role in shoreline protection, mangroves constitute a valuable tool in the fight against climate change. When a tree grows, it stores carbon in its biomass, thus decreasing the amount of carbon dioxide in the atmosphere. Mangroves perform this carbon storage mechanism particularly well, as they can store up to five times more carbon than an equal area of rainforest. These efficient carbon sinks are becoming increasingly relevant in the light of worsening climate change.

Source: http://www.ecologic.org/actions-issues/about-the-region/what-is-a-mangrove/

Source: http://www.esd-asiapacific.com/past/m_ecosystem/mg/function/index.htm

The diverse products and services generated by mangroves have traditional as well as commercial uses. The most direct product of a mangrove tree is its wood, which is used either as fuel or as a construction material. Other parts of the tree are also harvested to manufacture corks and floats, dyes, soap alternatives, synthetic fibers and cosmetics, and even food in the form of fruit, honey, vinegar, salt, or cooking oil. Furthermore, several mangrove species have significant medicinal properties. In addition to this wealth of different uses, mangrove ecosystems are well known for their important role in fisheries health. By providing a safe nursing ground for a wide range of fish larvae, they enhance the survival rate of these species in their early life stages.

Source: http://www.ecologic.org/actions-issues/about-the-region/what-is-a-mangrove/

Causes and consequences of loss of mangrove swamps

Source: http://www.ozcoasts.gov.au/conceptual_mods/processes/mangrove.jsp

Source: http://www.fishconserve.org/campaigns/coastal-2100/mangrove-conservation/

Although very complex and resilient to natural disturbances, mangrove ecosystems worldwide are endangered by human activity and are lost at a greater rate than inland tropical forests. Sea level rise and sedimentation off-balance the delicate adaptations of a mangrove tree to its environment, inhibiting its development or killing it off. Human-induced thermal, agrochemical, nutrient, heavy metal and oil-spill pollution also seriously impact this fragile ecosystem while deforestation and coastal development are one of its largest threats. Particularly, development pressures caused by a growing population and intensified shrimp farming activities cause large amounts of mangrove destruction.

Source: http://www.ecologic.org/actions-issues/about-the-region/what-is-a-mangrove/

Cutting mangroves and removing the woody structures not only terminates primary production and the sequestration of CO2, but also removes the physical lattice that supports the foodwebs of the flats ecosystem.  All terrestrial organisms that are not destroyed in the removal process must move to some other habitat to avoid predation and find food, which for most represents quite a challenge.  In addition, once the protective root system of the mangrove forest habitat is removed, to avoid predation, resident mobile marine organisms must quickly move to adjacent mangroves or alternative habitats.  Even if they are successful at that task, these immigrants also now have to compete successfully for space and food with the resident organisms f already there.  For smaller organism such as killifish or juvenile groupers, snappers, and bonefish, that success rate is likely small; local populations are often extirpated before they find alternative refuges.  The resident non-mobile species such as snails, worms, etc do not have the option of moving and so are usually quickly extirpated in place.

Beyond the simple removal of the mangrove plant itself, removing the sediments from around the roots of the mangrove also releases the carbon that had been sequestered in the anoxic sediments for many years.  Furthermore, the re-suspension of the sediment material in the surrounding waters during its removal together with the all too often run-off of the material deposited on land back into the ocean, kills other organisms in adjacent habitats, such as coral reefs and sea grass beds.  The overall effect is the total destruction of the nursery areas for juvenile lobster, grouper, snapper, and bonefish via the elimination of both their prey base and their protective refuge from predators.  The result of that is a reduction in the survival of juveniles, which results in fewer adults across the landscape.  In addition, surviving adults of these species that formerly used the mangrove forest as foraging areas now migrate away from the area in search of better alternatives.  The bottom line is that the removal of local mangrove patches can cause the numbers of individuals for key species to drop precipitously as the ability of the area to provide food for these top predators is reduced.

Source: http://www.fishconserve.org/campaigns/coastal-2100/mangrove-conservation/