Mangroves and climate change

Anais da Academia Brasileira de Ciências, 2015

Mangroves function as a natural coastline protection for erosion and inundation, providing important environmental services. Due to their geographical distribution at the continent-ocean interface, the mangrove habitat may suffer heavy impacts from global climate change, maximized by local human activities occurring in a given coastal region. This review analyzed the literature published over the last 25 years, on the documented response of mangroves to environmental change caused by global climate change, taking into consideration 104 case studies and predictive modeling, worldwide. Most studies appeared after the year 2000, as a response to the 1997 IPCC report. Although many reports showed that the world's mangrove area is decreasing due to direct anthropogenic pressure, several others, however, showed that in a variety of habitats mangroves are expanding as a response to global climate change. Worldwide, pole ward migration is extending the latitudinal limits of mangroves du...

Ecosystem Health and Sustainability, 2016

Historically, mangroves once covered over 200,000 km 2 of coastline globally (Duke et al., 2007). Climate change is expected to have a significant impact on mangroves via a number of processes, such as increased storminess, temperature and CO 2 as well as changes in rainfall (Ward et al., 2016). Sea level rise (SLR) is predicted to have the most significant physical, ecological and socioeconomic impacts on mangrove ecosystems. In the last halfcentury, 30% to 50% of mangroves have disappeared. This rate of loss is steady and in certain locations, even increasing (Godoy and Lacerda, 2015). Richards and Friess (2016) estimate a loss of 2 percent or ~100,000 hectares of mangroves between 2000 and 2012 in the SE Asian region alone. Furthermore, Duke et al (2007) write, 'mangroves are already critically endangered or approaching extinction in 26 out of the 120 countries having mangroves. In Indian Sundarbans due to increase of salinity stunted growth of mangroves have been observed and in certain patches of central Indian Sundarbans, extinction of Heritiera fomes has been reported (Mitra, 2013; Mitra and Zaman, 2014; Mitra and Zaman, 2015; Mitra and Zaman, 2016). Because of rise in temperature, alteration of salinity, precipitation etc. adverse impacts on mangrove ecosystem have been observed. The present study is a qualitative analysis on the basis of secondary data retrieved from several sources.

The word mangrove is being used in the Oxford English Dictionary since 1613, while the Americans, the Spanish and the Portuguese use the word ‘Mangle’ which is interpreted from the Haytaian Arawak language for the trees and shrubs of the genus Rhizophora. Later the word was modified as ‘Mangrove’ and included other tree genera growing in the intertidal zone and exposed to brackish water. At present the terms mangrove, or mangrove forest or mangrove ecosystem are commonly accepted and have become the synonym of tidal forest. Scientists theorize that the earliest mangrove species originated in the Indo-Malayan region. This theory is supported by the fact that there are more mangrove species present in this region than anywhere else in the world. Due to many species, unique floating propagules and seeds, early mangrove spread westward, by ocean currents, to India, East Africa, and eastward to the Americas, arriving in Central and South America during the upper Cretaceous period and lower Miocene epoch (66 and 23 million years ago). This may explain why the mangroves of the Americas contain fewer and similar colonizing species, while those of Asia, India, and East Africa contain a fuller range of mangrove species. Mangroves are basically salt tolerant forest ecosystems found mainly in tropical and sub-tropical inter-tidal regions. Till about 1960s, mangroves were largely viewed as “economically unproductive areas” and were therefore destroyed for reclaiming land for various economic and commercial activities. Gradually, with the passage of time, the economic and ecological benefits of mangroves have become visible and their importance is now well appreciated. It is now accepted that these rich ecosystems provide a wide range of ecological and economic products and services, and also support a variety of other coastal and marine ecosystems, which again provide several economic and ecological benefits. The full value of mangroves is, however, still not recognized in most economies, as most of these benefits have not yet entered the market (e.g., carbon credit from mangrove forest and soil). Consequently, mangroves have been highly undervalued and neglected ecosystems, resulting in their heavy depletion and degradation in most parts of the world. Recently researchers have initiated compiling their value in monetary terms in some parts of the world. Most of this valuation is for developed countries and even when it is for developing countries, the nature of benefits and costs estimated are very much different from the same in India, Indonesia, Sri Lanka, Pakistan or Bangladesh where mangroves play an extremely important role in the life and livelihood of coastal population. It is therefore a need to compute monetary value of mangroves in developing countries to understand its importance in the economic matrix. Today mangroves are observed in about 30 countries in tropical subtropical regions covering an area of about 99,300 Sq.Km. However during the past 50 years, over 50% of the mangrove cover has been lost, mainly because of the increased pressure of human activities like shrimp farming and agriculture, forestry, salt extraction, urban development, tourist development and infrastructure. Also, dam on rivers, contamination of sea waters caused by heavy metals, oil spills, pesticides and other products etc. have been found to be responsible for the decline of mangroves. Shrimp farming is directly linked to the loss of mangrove in tropical countries. About 2000 Sq.Km. in Vietnam, 350 Sq.Km. in India and 90 Sq.Km. in Bangladesh have been lost to shrimp farming. Climate change and subsequent sea level rise is also a major threat to mangrove ecosystems of the world. Researchers are of the opinion that mangroves may be affected by climate change-related increases in temperature and sea-level rise. Although the temperature effect on growth and species diversity is not known, sea-level rise may pose a serious threat to these ecosystems. In Bangladesh, for instance, there is a threat to mangrove species in the three distinct ecological zones (Hypersaline, mid saline and hyposaline regions) that make up the Sundarbans-the largest continuous mangrove area in the world. If the saline water front moves further inland, Heritiera fomes (the dominant species in the landward freshwater zone of Bangladesh and locally referred to as Sundari) could be threatened. Species in the other two ecological zones Nypa fruticans and Sonneratia apetala also could suffer. These changes could result severe adverse impacts on the socio-economic profile of the coastal zone. A large section of the population-who are directly employed in the industries that use raw materials from the mangrove forests (e.g., woodcutting, collection of thatching materials, honey, beeswax, and shells, fishing) - may lose their sources of income. Sea-level rise also may threaten a wide range of mammals, birds, amphibians, reptiles, and crustaceans living in the mangrove forests. Some ecologists believe that mangrove communities are more likely to survive the effects of sea-level rise in macrotidal, sediment-rich environments-such as northern Australia, where strong tidal currents redistribute sediment -than in microtidal, sediment-starved environments like those in many small islands (e.g., in the Caribbean). Most small islands fall within the latter classification; therefore, they are expected to suffer reductions in the geographical distribution of mangroves. Furthermore, where the rate of shoreline recession increases, mangrove stands are expected to become compressed and suffer reductions in species diversity in the face of rising sea levels. The present book addresses all these important issues in separate chapters with some interesting case studies whose data may serve as pathfinder for future researches in the sphere of the influence of climate change on mangrove ecosystem. According to me what seems to be needed, at the least is a massive programme of research and development to broaden the choices of alternative livelihood and a firm national and international commitment to mangal conservation instead of few sporadic afforestation programmes of mangrove species that are often taken up by the Government sectors and private organizations. The role of mangroves in the sector of bioremediation is a unique feather in the crown of this coastal and brackish water vegetation that may be taken up by the coastal industries in order to maintain the health of ambient environment. That the developing nations cannot afford to be without more brackish water related livelihood options is the general essence of this book. But policy questions such as those mentioned in chapter 2 (in the form of conservation policies) do not receive much attention here. Instead, this book seeks to discover and to assess the vulnerability of climate change on mangrove flora and fauna, their role in carbon sequestration and some interesting case studies by some groups of dedicated researchers that may serve as the basis of future climate related policies.

Interrelated and spatially variable climate change factors including sea level rise, increased storminess, altered precipitation regime and increasing temperature are impacting mangroves at regional scales. This review highlights extreme regional variation in climate change threats and impacts, and how these factors impact the structure of mangrove communities, their biodiversity and geo-morphological setting. All these factors interplay to determine spatially variable resiliency to climate change impacts, and because mangroves are varied in type and geographical location, these systems are good models for understanding such interactions at different scales. Sea level rise is likely to influence mangroves in all regions although local impacts are likely to be more varied. Changes in the frequency and intensity of storminess are likely to have a greater impact on N and Central America, Asia, Australia, and East Africa than West Africa and S. America. This review also highlights the numerous geographical knowledge gaps of climate change impacts, with some regions particularly understudied (e.g., Africa and the Middle East). While there has been a recent drive to address these knowledge gaps especially in South America and Asia, further research is required to allow researchers to tease apart the processes that influence both vulnerability and resilience to climate change. A more globally representative view of mangroves would allow us to better understand the importance of mangrove type and landscape setting in determining system resiliency to future climate change.

… of the Royal …, 2010

Geography Compass, 2017

2013