THE PROBLEM IN SUNDERBANaThephysiological response of an organism to increasing temperature follows asigmoid curve, in which an initial rapid rise in functional processes (e.g.,respiration, growth rate) slows, plateaus, and then declines as a criticallethal threshold is reached and then exceeded. Mangrove plants and animalspresumably respond so, but the critical temperatures at which functionalityplateaus and organisms begin to die are uncertain.
Rates of leaf photosynthesisfor most species peak at temperatures at or below 30 °C, and leaf CO2assimilation rates of many species decline, either sharply or gradually, astemperature increases from 33 to 35 °C. Photosynthesis in exposed leaves isoften depressed due to photo inhibition; mid-day declines of assimilation havebeen observed ensuring survival for the photochemical machinery. What hasbeen the response of mangroves in the field to the ongoing rise in temperature?Temperature increases alone are likely to result in faster growth,reproduction, photosynthesis, and respiration, changes in communitycomposition, diversity, and an expansion of latitudinal limits. Field dataindicate that mangroves are indeed currently expanding into higher latitudes inNorth America, New Zealand, Australia, southern Africa, and southern China.This global expansion poleward is most likely in response to the global rise insea surface temperatures. As thesechanges are occurring in the subtropics and tropics, mangrove expansion mayalso be coupled to changes in precipitation. In an analysis of mangrovelatitudinal changes, Quisthoudt et al.
found that temperature alone does notdelimit the latitudinal range of Rhizophora and Avicenna due partly to largeregional differences in monthly temperature change, for instance, warmest monthtemperatures are higher at the latitudinal limits in the northern, than in thesouthern, hemisphere. While mangrove expansion and salt marsh contraction areconsistent with the poleward increase in temperature and the reduction in thefrequency of extreme cold events, other variables such as changes inprecipitation cannot be ruled out as co-factors. Theexpansion of mangroves at the expense of salt marshes suggests that a number ofcomplex ecological interactions are operating during the transition. Proffittand Travis propose that this migration may be facilitated by increasingpropagule abundance from greater reproductive rates and greater geneticvariation caused by outcrossing. From field surveys conducted along theAtlantic and Gulf coasts of Florida, they found that reproductive frequenciesvaried significantly, but increased with latitude and more strongly along theGulf coast, with a concomitant increase in outcrossing.
The migration ofmangroves is self-re-enforcing; more colonizers lead to more propagules andoutcrossing leads to enhanced genetic variation, thus perpetuating andpromoting adaptation to a new environment. What effecthas the rise in temperature had and/or will have on mangrove-associated fauna?No studies have yet demonstrated a change in mangrove fauna associated withglobal warming, but the results from a few studies of macro- and megafauna fromadjacent habitats have implications for mangrove organisms. An experimentalstudy has shown that juvenile mullet (Liza vaigiensis) and crescent terapon(Terapon jarbua) frequenting tropical seagrass beds can be acclimated to higherwater temperatures, approaching the critical limits for marine vertebrates.Other organisms such as tropical gastropods may respond actively by seekingcooler sites to survive when temperatures exceed 33 °C. However, tropicalorganisms are closer to their upper thermal thresholds than boreal andtemperate organisms, and are thus more vulnerable to rising temperature. Mangroveresponses to increasing or decreasing precipitation are more straightforward,but such changes are likely to co-occur with rises in sea level, temperature,and atmospheric CO2 concentration. Compared to arid-zone stands, mangroveforests in the wet tropics have greater biomass and productivity, consist ofless dense but taller trees, and tend to inhabit finer sediment deposits, butthere are no clear species richness or diversity patterns between high and lowprecipitation areas; low species richness may be attributable to highvariability in annual rainfall. But mangroves clearly thrive in wetenvironments where they can likely deal less stressfully with lower salinityand more available fresh water.
ANNALYSIS AND PREDICTIONWhat then are we to predictabout the global future of mangroves in the face of climate change? There havebeen a number of general and local prognostications, especially in regard tosea level rise, but there have been few attempts at global prediction. Therehas been only one sophisticated attempt to forecast mangrove distributionsunder climate change. Using several mangrove databases for 30 species across 8genera, Record et al used the BIOMOD model to make predictions of mangrovespecies and community distributions under a range of sea level rise and globalclimate scenarios up to the year 2080. The model runs came up with two clearpredictions: some species will continue migrating poleward but experience a declinein available space; and Central America and the Caribbean will lose morespecies than other parts of the world. The latter prediction is in agreementwith the work of Polidoro et al in which extinction risk of threatened specieswas assessed and the main geographical area of concern was found to be theAtlantic and Pacific coasts of Central America.The recentclimatological forecasts by the Intergovernmental Panel on Climate Change(IPCC) for until the end of this century predict that globally sea surfacetemperatures will rise by 1–3 °C, oceanic pH will decline by 0.
07–0.31,and mean atmospheric CO2concentrations will increase to 441 ppm(from 391 ppm in 2011). Regional differences (Table 1) will occur for some parameters such as sea level,which will continue to rise globally at an average rate between 1.8 and2.
4 mm year?1; precipitation will increase and decrease insome regions such that arid areas will become more arid and the wet tropicswill become wetter; and salinity will change in tandem with changes inprecipitation. Considering these climatic predictions and the known and likelyresponses of mangroves to changes in temperature, salinity, sea level rise,etc. I offer somepredictions:· Prediction 1 (redlines): Mangrove forests along arid coasts will decline as salinities increase,freshwater becomes most scarce, and critical temperature thresholds are reachedmore frequently (e.g., NW Australia, Pakistan, Arabian Peninsula, both Mexicocoasts).
· Prediction 2(orange lines): Mangrove forests will decline as sediment yield declines,salinity increases, and sea level rises in tropical river deltas subject tosubsidence intervals (e.g., the Sundarbans; the Mekong, Zaire, Fly Rivers).
· Prediction 3(purple lines): Mangrove forests will decline as sea level rises and there islittle or no upland space to colonize (e.g., low islands of Oceania, manyCaribbean islands).· Prediction 4(blue lines): Mangroves forests will continue to expand their latitudinal rangeas temperature and atmospheric CO2 concentrations increase (NewZealand, USA, Australia, and China).MITIGATIONSTRATIGIESOver thelast several years, India has been pursuing a policy of energy conservation andincreased usage of renewable energy technologies. These measures have foundlegislative and regulatory backing. Taking this forward, the Central Governmentof India and the State Government of West Bengal are currently in the processof finalising an action plan, Titled ‘West Bengal State Action Plan on ClimateChange’ to address the problem of climate change and its impact on the Sundarbansas well as take steps for poverty alleviation. Noting the biological importanceof the Sundarbans as well the extreme human dependence on it sustenance, webelieve that neither a human-centric nor a pure conservation approach wouldhelp the long term health of the delta.
While the local population recognizesthe economic importance of the forests, extreme poverty has forced many toadopt certain practices that are harming the Sundarbans, already facing theonslaught of climate change. While making the entire Sundarbans or afforestationof all reclaimed areas may invite a sharp reaction from the millions of peopleinhabiting the area, we believe that the Government of India must take a middleground approach to balance out conservation needs of the area along with the humanneeds of the people. In this regard, in addition to India continuing to reduceits emissions and liaise with all governments to collectively reduce emissionsat an accelerated pace, we propose a series of short-term as well as long-term stepsto protect biodiversity of the Sundarbans and also improve the living conditionsof the people living in the area to help reduce the biotic pressure on thedelta and our mitigation strategies are set out below: A. MitigationStrategies that may be implemented immediately 1) Zoning Sundarbans according to vulnerability: The Government of WestBengal should demarcate specific areas of the Sundarbans that are particularlysusceptible to cyclonic storms. Upon completion of such demarcation, peopleliving in and around the high-risk areas in the Sundarbans should be strategicallyrelocated to safe inland areas. This is particularly relevant for those peoplewho live in the critically vulnerable areas of islands that are submerging orare frequently devastated by cyclonic storms.
Additionally, scientists have notedthat increased human and animal interaction has led to man-animal conflict.Therefore, protection patrols, surveillance of non-forest activities in theSundarbans areas and deployment of rapid action forces in case of conflictsituations should be deployed at the earliest. Such measures would go a longway in protecting the endangered animals in the region and building a relationshipof trust between the people, regulators and forests. 2) Regionalplanning and rehabilitation & relocation: Relocationof the population would be ineffective if the people are not given alternativejob opportunities. Such alternate job opportunities could include activelyparticipating in the conservation of Sundarbans (with individuals being deployedas forest guards or by generating employment in the tourism industry) or beingprovided jobs in cities and settlements close to Sundarbans. The long termsustenance of the Sundarbans is based on the people owning an economic stake inits conservation.
Since the Sundarbans are located close to Kolkata and otherurban settlements, the proximity could be utilised to promote tourism in thedelta, which would bring along with it additional sources of income.3) Creatingopportunities that don’t depend on nature: Forsuccessful rehabilitation and relocation, it is imperative that opportunitiesbe provided that do not depend upon nature. The StateGovernment will be required to invest in creation of infrastructuralfacilities, which while providing employment opportunities at the short term,will help the Sundarbans be a more accessible area for dissemination ofknowledge. Further, investments are required to provide education and health tothe local people. 4) Developingefficient disaster management systems: The StateGovernment must put in place effective early warnings systems. This must becommunicated to the people in real time and the people must be educated onexactly what to do in such circumstances. The State Government has to improveits evacuation systems, put in place rapid action response teams and be moreadept and efficient in providing supplies and first aid to people and animalscaught in such disasters. Further, there is a pressing requirement to set upanimal and human flood relief centres.
5) Protection& distribution of saline resistant food grains and seeds: Due to theextinction of certain traditional saline-resistant rice varieties as well as amarked increase in the salinity in the region, the State Government mustprotect remaining saline-resistant food grains and seeds that are saline resistantas well as increase distribution of such seeds at a subsidised rate to thelocal population.