Mangroves of Godavari – Analysis Through Remote Sensing Approach

The expansion of agriculture and aquaculture farms in the coastal areas has led to conversion of mangroves in the recent past. The extent of mangroves has also changed due to the erosion of mangroves along the coast and accretion near river mouths, leading to the formation of new mangrove areas. This study has been undertaken in the mangroves of the Godavari estuary, Andhra Pradesh, India to understand the changes in the extent of mangroves, namely accreted mangroves, erosion due to wave action and river water flow during floods, and changes due to forest restoration between 1986 and 2001, through remote sensing. The geomorphological changes due to river water flow in and around the mangroves have also been analysed. The changes in the vegetation due to forest restoration and natural regeneration are appreciable, while the changes in the area due to erosion and accretion are more or less equal. An analysis of the remote sensing images of 1986 and 2001 reveal that the mangroves outside the forest boundary have been converted to aquaculture. The sand spit of Hope Island has changed with time and has grown nearly 2.6 km between 1937 and 2001.     

海平面上升对粤港澳大湾区沿海生境脆弱性评估

全球气候变暖所导致的海平面上升和快速城镇化将对沿海生境的分布和景观格局造成重大影响。评估海平面上升影响下的滨海湿地的脆弱性是对区域生态环境进行修复治理的重要依据。以粤港澳大湾区为例,基于SLAMM模型和Fragstas模型,针对六种海平面上升和土地利用耦合情景,对红树林、盐沼和潮滩三类海岸生境在2100年的面积变化、分布状况和脆弱程度进行了预测和分析。结果表明:1) 随着海平面上升,红树林和潮滩生境遭受严重退化。其中,红树林高脆弱性区主要分布在西江口、珠江口和黄茅海东岸。潮滩高脆弱性区则平均分布在大湾区沿海地带。相比之下,盐沼生境受海平面上升的影响较小。2) 与红树林和潮滩相比,土地利用模式对盐沼生境的影响最为显著。在保护已开发用地的情景下,珠江口西侧的盐沼面积大幅增加,脆弱性程度低。在保护所有旱地的情景下,盐沼生境面积虽然基本维持,但景观格局破坏严重,脆弱性程度高。本研究建议针对高脆弱区,动态调整土地利用策略,清理沿海湿地向内迁移的空间,增强沿海生境应对海平面上升的适应性。本研究可为沿海湿地的管理和保护提供科学支持。     

The value of a mangrove area in Sarawak

Many arguments have been presented to justify the conservation of tropical forests. In the case of mangrove forests, their preservation can be argued using economic and employment grounds alone. A case study of the Sarawak Mangroves Forest Reserve, Malaysia is presented. Here, the mangroves support marine fisheries worth US$21.1 million p.a. and up to 3000 jobs, timber products worth US$123,217 p.a., and a tourist industry worth US$3.7 million p.a. If the mangroves were to be damaged, all of the fisheries and timber and many of the tourism benefits would be lost. In addition, highly expensive civil engineering works would be incurred to prevent coastal erosion, flooding and other damage. The area is also one of the only remaining refuges for mangrove flora and fauna in Sarawak. If the area were to be converted to aquaculture ponds or oil palm plantations, levels of revenue would be greatly reduced, and the multiple other benefits of mangroves would be lost. Coastal land pressure is not a limiting factor in the State. Considering their economic, employment, coastal protection and species conservation values, mangroves should be conserved and their importance taken into account at all levels in development planning.     

Effect of an integrated mangrove-aquaculture system on aquacultural health

Mangroves are unique intertidal halophyte formations growing in sheltered tropical and subtropical coastal areas. Due to the increasing population and economic development, mangroves have faced degrada-tion and loss, which has been mainly caused by land conversion into aquaculture ponds in Asia. In the past several decades, the rapid growth of aquaculture has induced water pollution. Using mangroves for effluent treatment from coastal aquaculture ponds could be a suitable approach for wastewater treatment and healthy aquaculture development. An Integrated Mangrove-Aquaculture System (IMAS) was established to test whether the idea of a mangrove in situ treatment for aquaculture wastewater is feasible. The monocultures of three mangroves, Sonneratia caseolaris, Kandelia obo-vata, and Aegiceras corniculatum were established with area proportions of 45%, 30%, or 15%, respectively. One control pond without mangroves was also set up. The results indicated that the mangroves had different toler-abilities to long-term inundation. The aquaculture ponds had different fishery yields, considering the mangrove species and area proportions. The water quality of most of the experimental ponds was better than the control pond, except for the planted Sonneratia. It is concluded that mangroves can reduce the concentration of dissolved inorganic nitrogen and phosphate, buffer the pH value and increase the concertration of dissolved oxygen in aqua-culture water bodies effectively. It is suggested to use 15% of the Aegiceras corniculatum area to conduct in situ purification of aquaculture wastewater and to enhance aquaculture production.     

沿海养殖池塘对红树林生态系统影响的时空变化监测与分析

随着沿海人类活动的日益加剧,其对红树林生态系统健康和可持续发展的影响也逐渐凸显,实现红树林周边典型人类活动时空动态变化监测对红树林生态系统的保护与修复意义重大。该研究基于Landsat多时相遥感数据和GoogleEarth Engine平台,通过面向对象的机器学习方法,融入水体季节波动信息作为分类特征,获取了1990、2000、2010和2020年4个不同时期中国沿海红树林分布省区(包括广东、福建、浙江、台湾、广西及海南) 30 m分辨率的养殖池塘空间格局及其变化特征,并进一步解析养殖池塘对红树林生态系统的影响。研究结果表明:(1)研究区域内4个时间节点的沿海养殖池塘面积总量分别为2 963、5 200、5 377及4 805 km²,呈先增加后减少的趋势,于2010–2020年间达到峰值。沿海养殖池塘面积变化趋势和达峰时间存在明显区域差异性,其主要原因是红树林保护政策、养殖池塘规范管理和阶段性经济目标的区域差异化。(2)我国沿海养殖池塘集中分布在21°–24°N区域(广东和广西),与红树林沿纬度的分布格局呈错峰分布。其中,红树林与沿海养殖池塘集中分布区(21°–...     

Effect of an integrated mangrove-aquaculture system on aquacultural health

Mangroves are unique intertidal halophyte formations growing in sheltered tropical and subtropical coastal areas. Due to the increasing population and economic development, mangroves have faced degradation and loss, which has been mainly caused by land conversion into aquaculture ponds in Asia. In the past several decades, the rapid growth of aquaculture has induced water pollution. Using mangroves for effluent treatment from coastal aquaculture ponds could be a suitable approach for wastewater treatment and healthy aquaculture development. An Integrated Mangrove-Aquaculture System (IMAS) was established to test whether the idea of a mangrove in situ treatment for aquaculture wastewater is feasible. The monocultures of three mangroves, Sonneratia caseolaris, Kandelia obovata, and Aegiceras corniculatum were established with area proportions of 45%, 30%, or 15%, respectively. One control pond without mangroves was also set up. The results indicated that the mangroves had different tolerabilities to long-term inundation. The aquaculture ponds had different fishery yields, considering the mangrove species and area proportions. The water quality of most of the experimental ponds was better than the control pond, except for the planted Sonneratia. It is concluded that mangroves can reduce the concentration of dissolved inorganic nitrogen and phosphate, buffer the pH value and increase the concertration of dissolved oxygen in aquaculture water bodies effectively. It is suggested to use 15% of the Aegiceras corniculatum area to conduct in situ purification of aquaculture wastewater and to enhance aquaculture production.     

Assessing wetland services for improved development decision-making: a case study of mangroves in coastal Bangladesh

Mangroves provide valuable ecosystem services for the wellbeing of coastal communities. Assessment and valuation of these mangroves services are increasingly advocated in development and conservation decision-making. Translating the values of services into more explicit monetary terms requires understanding of stakeholder activities, socio-economic context and local organizational structure to effectively support decision-making. Based on a survey of 100 households of three villages of Sundarban in Bangladesh, mangroves services to local communities were identified and their economic values estimated. The households perceived 18 mangroves services, of which capture fisheries, fuel energy, storm protection, habitat for fish breeding and nursery grounds and aesthetic enjoyment were ranked the most important. For provisioning services, households obtained important monetary benefits annually from capture fishery (US$ 976 per ha), fuel energy (US$ 80 per ha), honey (US$ 53 per ha) and fodder (US$ 26 per ha). The average annual willingness to pay for storm protection, erosion control and habitat for fish breeding and nursery services were estimated, respectively, as US$ 13 per ha, US$ 2 per ha and US$ 9 per ha. However, unsustainable exploitation and salinity intrusion impacted the services provided by mangroves. This study provides an important insight into the services and values of mangroves for local welfare, and thus can inform policy for protection and better use of mangrove resources.     

Depletion of the mangroves of Continental Asia

The mangroves located around the Bay of Bengal and along the coast ofSouth China Sea are of special interest for many reasons. This coastlinereceives three major tropical rivers (Ganges, Irrawaddy, Mekong) and it hasthe world's largest mangrove stands in a single block (the Sunderbans). Thecontrasted climatic conditions from sub-arid (southeastern India), to moist(coastal Cambodia), and the extreme diversity of human impacts in one ofthe world's highest population densities (West Bengal in India andBangladesh), have created a mosaic of mangrove types that are floristicallyrich and with different histories, different ecological frameworks and distinct evolutionary trends.For the first time, we draw together remote sensing data along withessential structural and physiognomic parameters of mangrove forest areas.We have devised a sufficiently accurate coastal mapping methodologyproviding statistics on the actual areal extent of mangrove types andsub-types, both at local and continental scales. Some results are entirelynew, and others provide comparison with existing data. The exact extentof mangroves in Myanmar was previously unknown. Using remote sensingwe also demonstrate the magnitude of the ongoing deforestation in thiscountry. The current location and status of mangrove forests in the affectedarea are described using the methodology which is also being applied inother sites around the world.     

Metabolic diversity and bioactivity screening of mangrove plants: a review

Mangrove forests are salt tolerant plants confined to the coastal areas and occupy only 5% of the total forest areas of the world. These are the most hostile environment with fluctuating tidal and saline regime and a limited plant species can survive under such condition. Nevertheless, these plants are most valuable resources and provide economic and ecological benefits to the coastal people. Several mangrove species have been used in traditional medicine or have few applications as insecticide and pesticide. Mangroves are biochemically unique, producing wide array of natural products with unique bioactivity. They possess active metabolites with some novel chemical structures which belong to diverse chemical classes such as alkaloids, phenol, steroids, terpenoids, tannins, etc. The present review examines recent investigations on the biological activities of extracts and phytochemicals identified from mangroves and their associates as antimicrobial, antiviral, antioxidant, anticancer and many other properties like antiproliferative, insecticidal, antimalarial, antifeedant, central nervous system depressant and anti-plasmodial etc. The present article also emphasizes and creates an awareness of potential mangroves and their associates as a source of novel medicines, agrochemicals and source of many biologically active compounds.     

Participatory appraisal for potential community-based mangrove management in East Africa

Mangroves are among the most threatened ecosystems in the world and the coastal forests of East Africa are no exception to this trend. Although conservation, rehabilitation and sustainable management plans have been developed in various tropical regions, only a few locally based approaches have been launched along the Indian Ocean coast of Africa. In order to identify possible conditions for sustainable management of mangroves based on socio-economic and ecological considerations, we present a participatory approach designed to evaluate the relationships between mangroves and human activities and the use of multi-criterion analysis to identify management solutions. To achieve this goal, all the subjects involved in mangrove management (local communities, institutions and researchers) took an active part in the process. The research was carried out in three communities relying on mangrove swamps: Kisakasaka village on the island of Zanzibar, Mida Creek in Kenya, both relying on mangrove forests known to be endangered by over-exploitation, and Inhaca Island in Mozambique, where mangroves are more pristine. Families were the hub of the research and the importance of each of their economic activities was assessed. We then examined the methods by which mangroves are exploited by the local community and by other stakeholders working in the study areas. Our results show that the mangroves in Inhaca are exploited only for household needs and the pressure on the forests is still ecologically sustainable. In contrast, there is a well-established demand for mangrove products in Kisakasaka and Mida Creek and the mangroves represent an essential source of income for the families, resulting in an ecologically unsustainable rate of exploitation. Therefore, possible alternatives to the current management practices were identified in the two areas by means of a participatory approach. Multi-criterion analysis was then used to compare and discuss the alternatives in terms of social, economic and ecological criteria.     

Effects of mangrove soil ageing on the accumulation of hydrogen sulphide in roots ofAvicennia spp

The possibility for accumulation of hydrogen sulphide gas in roots of mangroves (Avicennia spp) which had colonized reclaimed coastal areas in Singapore was investigated using a simple potentiometric technique preceded by an extraction step. The study showed that detectable amounts of hydrogen sulphide gas were present in the underground cable roots of the mangroves and that the concentrations increased with the age of the plant. Furthermore concentrations of hydrogen sulphide in the roots were 30–40 times higher than the concentrations of the gas which were simultaneously generated by anaerobic processes in the surrounding, ageing mangrove sediment. The reasons for these patterns and their possible impact on the succession ofAvicennia spp by a different type of mangrove,Rhizophora spp, are discussed.Author to whom correspondence should be addressed     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

A review of the role of fish as biological control agents of disease vector mosquitoes in mangrove forests: reducing human health risks while reducing environmental risk

The saltwater mosquito, Aedes vigilax, is prolific in coastal wetlands including mangroves and saltmarshes. Ae. vigilax is a vector for arboviruses such as Ross River and Barmah Forest viruses, with significant consequences for human health and economic productivity. In Australia the dominant form of mosquito control is chemicals. For mangroves, this is because there is a critical lack of knowledge supporting alternative approaches, such as environmental modification or biological control using larvivorous fish. This review examines the potential of fish as biological agents for the control of mosquito larvae in mangroves. We consider two key aspects: how larvivorous fish use mangroves; and can larvivorous fish reduce larval mosquito populations sufficiently to provide effective mosquito control? The link between fish and mangroves is reasonably well established, where mangroves act as refuge habitat for small and juvenile fish. Also, research has established that fish can be significant predators of mosquitoes, and therefore may be effective control agents. However, studies of fish activity within mangroves are limited to study of the fringe of the mangroves and not the internal structure of mangrove basins and as a result, fish populations within these areas remain unstudied. Also, until recently there was little appreciation of the mangrove-mosquito habitat relationship and, as a consequence, the importance of the mangrove basin as the key mosquito habitat has also been overlooked in the literature. Similarly, the predator/prey relationships between fish and mosquitoes within mangrove basin environments also remain unstudied, and therefore the importance of fish for mosquito management in mangrove basins is not known. There are substantial knowledge gaps regarding the potential of fish in controlling larval mosquitoes in mangroves. The gaps include: understanding of how larvivorous fish use mangrove basins; the nature of the fish-mosquito predator/prey relationship in mangrove basins; and whether larvivorous fish are effective as a mosquito control option in mangroves.     

Recognition of co-existence pattern of salt marshes and mangroves for littoral forest restoration

Climate-change driven sea level rise causes a increase in salinity in coastal wetlands accelerating the alteration of the species composition. It triggers the gradual extinction of species, particularly the mangrove population which is intolerant of excessive salinity. Thus despite being crucial to a wide range of ecosystem services, mangroves have been identified as a vulnerable coastal biome. Hence restoration strategy of mangroves is undergoing rigorous research and experiments in literature at an interdisciplinary level. From a data-driven perspective, analysis of mangrove occurrence data could be the key to comprehend and predict mangrove behavior along different environmental parameters, and it could be important in formulating management strategy for mangrove rehabilitation and restoration. As salt marshes are the natural salt-accumulating halophytes, mitigating excessive salinity could be achieved by incorporating salt-marshes in mangrove restoration activities. This study intends to find a novel restoration strategy by assessing the frequent co-existence status of salt marshes, with the mangroves, and mangrove associates in different zones of degraded mangrove patches for species-rich plantation. To achieve this, we primarily design a novel methodological framework for the practice of knowledge discovery concerning the coexistence pattern of salt marshes, mangroves, and mangrove associates along with environmental parameters using a data mining paradigm of association rule mining. The proposed approach has the capability to uncover underlying facts and forecast likely facts that could automate the study in the field of ecological research to comprehend the occurrence of inter-species relationships. Our findings are based on published data gathered on the Sundarban Mangrove Forest, one of the world’s most important littoral forests. The existing literature reinforces the findings that include all the sets of frequently co-occurring mangroves, their associates, and salt marshes along the salinity gradient of coastal Sundarbans. A detailed understanding of the occurrence patterns of all these, along with the environmental variables, would be able to promote decision-making strategy. This framework is effective for both academia and stakeholders, especially the foresters/ conservation planners, to regulate the spread of salt marshes and the restoration of mangroves as well.     

The Loss of Species: Mangrove Extinction Risk and Geographic Areas of Global Concern

Mangrove species are uniquely adapted to tropical and subtropical coasts, and although relatively low in number of species, mangrove forests provide at least US $1.6 billion each year in ecosystem services and support coastal livelihoods worldwide. Globally, mangrove areas are declining rapidly as they are cleared for coastal development and aquaculture and logged for timber and fuel production. Little is known about the effects of mangrove area loss on individual mangrove species and local or regional populations. To address this gap, species-specific information on global distribution, population status, life history traits, and major threats were compiled for each of the 70 known species of mangroves. Each species'' probability of extinction was assessed under the Categories and Criteria of the IUCN Red List of Threatened Species. Eleven of the 70 mangrove species (16%) are at elevated threat of extinction. Particular areas of geographical concern include the Atlantic and Pacific coasts of Central America, where as many as 40% of mangroves species present are threatened with extinction. Across the globe, mangrove species found primarily in the high intertidal and upstream estuarine zones, which often have specific freshwater requirements and patchy distributions, are the most threatened because they are often the first cleared for development of aquaculture and agriculture. The loss of mangrove species will have devastating economic and environmental consequences for coastal communities, especially in those areas with low mangrove diversity and high mangrove area or species loss. Several species at high risk of extinction may disappear well before the next decade if existing protective measures are not enforced.     

红树植物水分关系研究进展

红树林生长于受潮汐影响的海滨特殊生境,具有重要的生态功能及应用价值。红树植物的水分利用特点一直是研究热点。由于受环境盐分影响,红树植物水势普遍较低;水分运输系统抗气穴化能力极强;水分利用保守,用水量处于同径级的热带陆生树木用水量的低值范围;表型可塑性大,可通过耐旱、耐盐和多样的水分管理策略适应潮间带环境;水分运输效率不低,能在环境条件适宜时进行高效的光合合成。本文通过大量的文献分析,综述了红树植物的水分关系特点、水分和盐分管理策略,对未来从多角度、结合新研究技术的红树植物水分关系研究进行了展望。     

Environmental drivers in mangrove establishment and early development: A review

Mangroves have a global distribution within coastal tropical and subtropical climates, and have even expanded to some temperate locales. Where they do occur, mangroves provide a plethora of goods and services, ranging from coastal protection from storms and erosion to direct income for human societies. The mangrove literature has become rather voluminous, prompting many subdisciplines within a field that earlier in the 20th century received little focus. Much of this research has become diffuse by sheer numbers, requiring detailed syntheses to make research results widely available to resource managers. In this review, we take an inclusive approach in focusing on eco-physiological and growth constraints to the establishment and early development of mangrove seedlings in the intertidal zone. This is a critical life stage for mangroves, i.e., the period between dispersal and recruitment to the sapling stage. We begin with some of the research that has set the precedent for seedling-level eco-physiological research in mangroves, and then we focus on recent advances (circa. 1995 to present) in our understanding of temperature, carbon dioxide, salinity, light, nutrient, flooding, and specific biotic influences on seedling survival and growth. As such, we take a new approach in describing seedling response to global factors (e.g., temperature) along with site-specific factors (e.g., salinity). All variables will strongly influence the future of seedling dynamics in ways perhaps not yet documented in mature forests. Furthermore, understanding how different mangrove species can respond to global factors and regional influences is useful for diagnosing observed mortality within mangrove wetlands, managed or natural. This review provides an updated eco-physiological knowledge base for future research and reforestation activity, and for understanding important links among climate change, local physico-chemical condition, and establishment and early growth of mangrove seedlings.     

Carbon stocks of mangroves and losses arising from their conversion to cattle pastures in the Pantanos de Centla,Mexico

The conservation of mangroves and other coastal “blue carbon” ecosystems is receiving heightened attention because of recognition of their high ecosystem carbon stocks as well as vast areas undergoing land conversion. However, few studies have paired intact mangroves with degraded sites to determine carbon losses due to land conversion. To address this gap we quantified total ecosystem carbon stocks in mangroves and cattle pastures formed from mangroves in the large wetland complex of the Pantanos de Centla in SE Mexico. The mean total ecosystem carbon stocks of fringe and estuarine tall mangroves was 1358 Mg C/ha. In contrast the mean carbon stocks of cattle pastures was 458 Mg C/ha. Based upon a biomass equivalence of losses from the top 1 m of mangrove soils, the losses in carbon stocks from mangrove conversion are conservatively estimated at 1464 Mg CO₂e/ha. These losses were 7-fold that of emissions from tropical dry forest to pasture conversion and 3-fold greater than emissions from Amazon forest to pasture conversion. However, we found that limiting ecosystem carbon stocks differences to the surface 1 m or even 2 m soil depth will miss losses that occurred from deeper horizons. Mangrove conversion to other land uses comes at a great cost in terms of greenhouse gas emissions as well losses of other important ecosystem services.