The ecology of the Sundarbans

The ecology of the Sundarbans

By Dr.Fourkian Ali

The Sundarbans soil is characterized as moderately to slightly saline zone in the east and highly saline zone in the west. Its ecosystem is characterized by a very dynamic environment due to the effect of tide, flooding, salinity and even the cyclone. The fragile and intricate mangrove ecosystem depends on many variable components like tides, salt contents in water and soil, duration of sunlight, contents of sediment and organic matter in water; temperature and density of seawater and fresh water. The composition of terrestrial and marine flora and fauna also plays an important role in die mangrove ecosystem. If sun is regarded as the source of all energy flow water must be considered as the nursing mother of an ecosystem.

In the Sundarbans, the flow of fresh water received from the tributaries of the Ganges (Padma) is lighter in turbidity than that of the Bay of Bengal waters. The temperature of the two waters also varies seasonally. The fresh water carries loads of mineral and microbe-rich silts, which do not flow easily into the tidal backwaters from the sea as the influence of the tides make the water flow back and forth. The mixture of the flows of fresh water and brackish water and the mineral-microbe silts from upstream and due forest wastes like over mature leave creates an ideal environment for different mangrove organisms.

As the forest litters and other organic materials are transported in the channels the microorganisms like bacteria and fungi starts to decompose them convening tl1em into minerals and nutrients. These are then used by phytoplankton and insects like acron worms, nematodes and amphipods. In turn the micro organisms themselves become a source o food for small aquatic animals, which too are preyed upon by shrimps, crabs etc. The zooplanktons are again the food source for different aquatic animals like fishes, catfish, eels, groupers and giant sea perches. The planktons also provide food to sharks, crocodiles, and dolphins. In this process some die, decay and become nutrients accumulated in the mangrove soil. The amphibians and the reptiles act as connecting agents between water-based energy flow and terrestrial energy flow In the Sundarbans, the higher order animals like the tiger wild boar and monkey supplement their diet by eating aquatic animals and fishes.

“Zonation" often characterizes mangrove forests. Certain tree species occupy particular areas, or niches, within the ecosystem. Some mangrove species occur close to shore, fringing islands and sheltered bays; others are found further inland, in estuaries influenced by tidal action.

The largest mangrove forest of the world is under threat

Mangrove forests are one of the most productive and bio-diverse wetlands on earth. Yet, these unique coastal tropical forests are among the most threatened habitats in the world as experts’ fear they may disappear more quickly than inland tropical rainforests because of lack of public notice. The Sundarbans too is no exception.

Most experts agree that due to direct and indirect impact of human interventions, far-reaching changes are taking place slowly but steadily -- affecting the delicate Sundarbans ecosystem. Much of such changes are not clearly visible. Direct human impacts are further worsened by the less-readily detected but perhaps more menacing impacts which threaten the mangrove ecosystem. Massive changes in both the adjacent agricultural lands and upstream areas with construction of polders, embankments or barrages are feared to have been generating fundamental changes in the hydrological regime of the Sundarbans.

The changes in freshwater flushing are visibly caused by gradual eastward shift of the flow of the Ganges river, The change is acknowledged as being historical in nature although the more recent impact of e Farakka Barrage in India and subsequent siltation in the Gorai is accelerating the process. It is believed that the changes affecting the salinity flood intensity and periodicity erosion, siltation. and sedimentations may all be factors for perplexing and worrisome loss m the world's largest mangrove system.

A number of species like Javan rhinoceros (Rhinoceros sondaicus), water buffalo (Bubalus bubalis), swamp deer (Cervus duvauceli), gaur (Bos gaurus), hog deer (Axis porcinus) and marsh crocodile (Crocodilus palustris) became extinct during the last 100 years from the Sundarbans.

The Royal Bengal 'Tiger is an inseparable part of the legend attached to the Sundarbans. The tidal mangrove forest is a rare habitat for this tiger species. But today they have been pushed due to habitat shrinkage. The SRF tiger population estimate in the past 20 years remained in the range of 550 to 400, the largest discrete population of the species in a single tract of natural habitat in the world.

But the preservation of the Royal Bengal Tigers is, by far; the most important challenge for those concerned for the protection of Sundarbans bio-diversity This challenge has become even more compelling of late with recent media reporting of the outcome of a tiger population in the Indian part of Sundarbans where the number of tigers was once estimated at something similar to that in the Bangladesh part - i.e. 300+. The figure is now down to some 50 only.

Incidental mortality due to diseases, illegal hunting and subtle changes in the Sundarbans ecosystem poses a serious risk for the survival of the Royal Bengal Tiger Apart from that, the interaction with humans in the area particularly the killing of humans by tiger complicates the management of the area. IUCN has listed it as an endangered species in its Red Book.

The marsh crocodiles, once abundant, are already extirpated. The salt- water crocodile (Crocodiles porous) still survives in low densities and like the marsh crocodiles its population is being reduced through indiscriminate hunting and trapping for skins, quite apart from the immediate conflict with men. Despite an apparent reduction in illegal trade in its skin, the population shows little sign of recovery.

Some 30 species of snakes have been recorded in the SRF and there appears to have been a general decline in densities or at least in their sighting particularly in the past two decades. The Rock Python (Python molars) is one of the valuable SRF snake species, which is said to have declined over recent years. IUCN has listed it as a "vulnerable species."               

The results of four independent inventories undertaken over the past seventy years indicate that the overall volume of wood per hectare has decreased. Moreover; closer analysis of three inventories undertaken in 1959, 1983 and 1996 indicate a marked reduction in total standing volume for the two principal species of economic importance, Sundari and Gewa.

According to studies carried out at different times by the forest department, British ODA and UNDP/FAO sponsored Forest Resource Management Plan, the mean volume per hectare of the Sundari tree was 54.5 in 1959. The volume was reduced to 19.9 in 1985 and 17.8 in 1996. In case of Gewa, the mean volume per hectare was 8.7 in 1959, which was reduced to 4.6 in 1985, and 2.1 in 1996. The dramatic decrease is blamed on their over exploitation, legally and illegally because of their commercial value and subtle changes in the ecosystem. A number of issues related to the Sundari, Gewa and Goran trees have emerged for immediate concerns of the foresters.

According to experts, the reasons for the decline in Sundari (Heriteria fomes) are twofold. First, as a valuable timber species with real commercial value, it has been subject to heavy exploitation. Second, increasing salinity as a subsequent impact of the subtle ecological changes, noticeable increase in salinity and siltation have resulted in hostile anaerobic conditions in which the Sundari finds it difficult for healthy respiration. This has resulted in die-back whereby the tree is progressively defoliated from the top downwards. The phenomenon, in act an infectious disease, is called "top dying," The infectious top- dying disease of Sundari causes another management problem as experts said poor execution of infected trees invalidate the basic rationale for the "sanitation/salvage" method to save the uninfected trees. Long delays between marking and cutting causes more trees in an area affected by top dying eventually exposing them to "axes instead of saws."

With regard to Gewa, forest officials say high pressure from deer population in some areas of forest patches have spared or caused nil regeneration of the species, leaving the areas under-stocked. The decline in Gewa (Excoecaria agallocha) is largely attributable to harvesting of around 50,000 m3 per annum as feedstock to Khulna Newsprint Mill for the production of newsprint over the years.

Experts say there is apparently little respect for the basic rule of leaving one stout stem to aid re-growth while cutting Goran trees, the second largest tree species of the SRF as all available merchantable stems are being cut from one area. Some officials admit there is also Goran cutting going on outside the coupe areas, including the wildlife sanctuaries. However, acknowledging the importance of forest resources exploitation on a sustainable basis, the Forest Department imposed a logging moratorium in 1989 on all timber species except Gewa in the SRE.

Many factors contribute to mangrove forest loss, including the charcoal and timber industries, legal and illegal logging, oil spill, tourism industries, unplanned development protects, urban growth pressures, and mounting pollution problems. However one of the most  recent and significant muses of mangrove forest loss in the past decade has been the consumer demand for luxury shrimp, or "prawns", and the corresponding expansion of destructive production methods of export-oriented industrial shrimp aquaculture along the forests.

No discussion of the ecology of the SRF would be complete without noting the problem of water pollution, Pollution from various sources is a major determinant of water quality -- both in reverie and coastal areas of the Sundarbans. As approximately one third of the nearly 600,000 hectares of the Sundarbans area consists of tidal channels, and most of the reminder is subject to periodic inundation, impacts of water pollution are potentially very widespread, Pollutants are carried into the Sundarbans and ultimately into the Bay of Bengal from various upstream sources including the industrial units, municipal wastes, agrochemicals and port sewages in the Mongla and Khulna region.

The main threat today may come from outside the area in the form of pollution. On the northern edge of the area, Mongla, Bangladesh second seaport is situated, this port and its associated marine traffic is a frequent source of oil spills and there is a permanent risk of, accidents with chemicals. Moreover toxic products (pesticides, etc.) enter the system due to upstream pollution in the huge Ganges catchments. Pollution may not be a direct source of mortality, but it may also reduce the health of the forests, increasing the mortality rate of the flora and fauna on the long term. Many products such as pesticides have also been proved to reduce the reproductively (birthrate) in animal populations.

Almost all Khulna-based industries like the match factories, fish processing plants, jute mills, steel mills, the Khulna Shipyard and newspaper mills discharge liquid or solid wastes directly into the Bhairab-Rupsha river system. According to a DOE paper, the Khulna Newspaper Mills alone is estimated to use and discharge 50,000 m3 of processed water laden with chlorides and dissolved and suspended solids everyday along with the municipal wastes of the regional cities.

Oil spills during transfer of refined petroleum from tankers to receiving stations in Mongla and Khulna, fuel oil spillage and discharge of oily ballast and sewages from some 600 ships anchored in Mongla Port and residual heavy oil sludge, lubricants and engine oils discharged during ship breaking operations in Khulna are major sources of water pollution affecting the Sundarbans.

A future threat is the exploitation of mineral gas, which is abundant in the underground of the Sundarbans, The recent government decision to allow exploration by international oil giants in the area has caused added concerns, as mangrove environments are known to be the most vulnerable coastal habitats to such activities.

A very densely populated area surrounds the SRE around 1.2 million local users reside seasonally in the area for fishing and outer resource use activities. Commercial hunting was a problem mainly before the 19705 and this resulted particularly in a serious depletion of the crocodile populations and to a lesser extent to the deer population, Although wildlife protection has improved significantly in the last decades, illegal hunting is still occurring on an incidental basis and fishery is having an adverse impact on the remaining turtle and crocodile populations as these animals are frequently caught up in fishing nets.

Due to natural processes the role of the Sundarbans to discharge the water of the Ganges and Brahmaputra catchments is decreasing as main waterways are shifting eastwards. As a result, the salinity of the Sundarbans is increasing -- particularly in the western region. Further, the total annual discharge is decreasing due to intensifying land use (dams, irrigation) upstream. The role of this change is not yet clear, but is evident that it will influence wildlife populations and vegetation in the long term,

The expanding shrimp farming in the greater Khulna region has caused wide concerns for the rich bio-diversity of the Sundarbans. Experts say indiscriminate shrimp and salt cultivation already destroyed the valuable mangrove forest in Chakoria Sundarbans and fear that the ecosystem of the SRF too would be in jeopardy for the same reason in the near future. The fisheries department reckons that some 200 billion different fish fries are destroyed every year in course of gathering two billion shrimp fries from the water bodies along the Sundarbans due to the crude methods adopted for the purpose.

                                         

Several international reports suggests that vast tracts of mangrove forests particularly in Latin America, Africa and the Pacific Islands have been cleared to make way for the establishment of coastal shrimp farm facilities. The failure of national governments to adequately regulate the shrimp industry and the headlong rush of multilateral lending agencies to fund aquaculture development without meeting their own stated ecological and social criteria, are other important pieces to this unfortunate puzzle.

The great earnings from the shrimp sector are short-lived, while the real posts of shrimp culture in terms of consequent environmental ruin and social disruption are long-term and astronomical. While the immediate profits from shrimp farming may satisfy a fog vast numbers of coastal residents, once dependent on healthy coastal ecosystems for fishing and farming, are being displaced and impoverished. Observers believe that the environmental and social losses would eventually eclipse profits from the shrimp sector.

Forest department officials admit that though slowly far-reaching changes are taking place pervasively in me Sundarbans. These arise from direct and indirect impacts of human influence in the area causing widespread quantitative and qualitative degradation of the resource base throughout the Sundarbans eco-system, According to forest inventory it is clear that the level of illicit takeoff, some purely illegal and some quasi-sanctioned, may be quite larger than what could be scientifically justified for sustainable management of the SRF.

The expanding tourism trade is appearing to be another major concern for the protection of the Sundarbans. Except the conscious tourists or tour operators, others tend to knowingly or unknowingly disturb the delicate ecosystem of the Sundarbans staging bonfires, playing loudspeakers or disposing of non-degradable wastes like polythene inside the forest, sea shores or water bodies. That should be stopped.

Consequence of mangrove deforestation

In many areas of die world, mangrove deforestation is contributing to fisheries declines, degradation of clean water supplies, Stalinization of coastal soils, erosion, and land subsidence, as well as the release of carbon dioxide into the atmosphere. In fact, mangrove forests fix more carbon dioxide unit area than phytoplankton in tropical oceans. With regard to the Sundarbans, experts have sounded caution that destruction of the forest will not only affect the ecology but cause far reaching impacts on national economy and causing immense damage to the marine resources of the Bay of Bengal, still economically unexplored and unexploited by Bangladesh. The loss of the Sundarbans would also expose the entire southwestern region of the country to frequent cyclones and tidal surges.

Mangrove forests once covered three-fourths of the coastlines of tropical and sub-tropical countries. Today less than 50 percent of that is surviving. And then again, of this remaining mangrove forests, over 50 percent has been degraded and not in good form, Greater protection measures should be taken for maintaining high quality mangrove forests like the Sundarbans - a World Heritage Site. All said and done, future sustainability of the Sundarbans depends upon the political will of the policy makers, environmental awareness of the people and the improved management and conservation by the forest department and other concerned agencies.