is at the forefront of global mangrove conservation. It is the first country to officially protect all its remaining mangrove forests and has embarked on an ambitious plan to restore 10,000 ha of wetland during the United Nations Decade of Ecosystem Restoration. One incentive for this conservation effort is a recognition, based on research mostly done elsewhere, of the importance of mangroves for carbon sequestration and storage. However, a lack of data on Sri Lankan mangrove carbon pools, especially on soil organic carbon, has been recognized as a major impediment to national climate change mitigation strategies. The current work examined both above and below-ground carbon stocks of five important mangrove forests in Sri Lanka (Rekawa, Puttalam-Kalpitiya, Pambala-Chilaw, Batticaloa and Negombo) which are situated in the three major climate zones (dry, intermediate and wet) and therefore sample the main climatic drivers of spatial variability. Above-ground carbon, below-ground root carbon and soil carbon stocks of mangroves in Sri Lanka ranged from 75.5 to 189.1 Mg C ha − 1 , 7.9 to 14.3 Mg C ha − 1 and 643.6 to 1253.6 Mg C ha − 1 , respectively. The highest total mangrove carbon stock was recorded from the Rekawa lagoon which is in the intermediate climate zone (1455.4 Mg C ha − 1 ) while the lowest was found in the Batticaloa lagoon in the dry zone (734.7 Mg C ha − 1 ). Soil carbon stocks were substantially higher in the places where vegetation biomass and stand densities are high. Soil comprised 83-90% of the total mangrove carbon stocks at all sites, highlighting the large potential for release into the atmosphere as carbon dioxide if these habitats are disturbed. Overall, our study contributes important data that broadens our current understanding of how mangrove organic carbon pools vary spatially and with climatic zone.

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The behaviour of carbohydrate metabolism in a plant, particularly its total starch content, total soluble sugar (TSS) content and their utilisation, is of great importance in coping with abiotic stress conditions. With this in mind, we studied total starch and TSS contents, survival, growth, biomass accumulation and stomatal conductance in Rhizophora mucronata under conditions of prolonged submergence and water stress for a period of 11 months. The experiment was designed in such a way as to include three replicates per each treatment level, about 1600 young mangrove plants being subjected to study in the process. Under conditions of prolonged submergence and high levels of water stress, a small number of mangrove plants survived and they were promptly exhausted due to higher starch utilisation rates (0.75-1.05% dry mass/month). Although TSS content was increased under these intense stress conditions, it was not matched by increased seedling growth or biomass production; instead, a significant reduction in growth (i.e., ~78%) and dry matter content was observed in stressed seedlings as compared to young plants in the respective controls. It follows that the intense increase of TSS content might be due to the direct conversion of starch to soluble sugars in order to produce metabolic energy for tolerance mechanisms like osmoregulation and root anatomical adaptations under stress conditions. This indicates that more energy is allocated for plant maintenance than for growth and biomass production under stress conditions, which might be a good acclimatory strategy to rescue young mangrove plants at the early phase. However, stomatal closure under stress conditions may have caused restricted photosynthesis. Therefore, stress-induced starch degradation may upsurge, which in turn might lead in the long-run to carbon starvation, a condition lethal to mangrove seedlings.

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Spatio-temporal changes during the last twelve year period (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017) and their impacts on ecological and socio-economic status of Dondra lagoon, southern coast of Sri Lanka were studied as many lagoons in southern Sri Lanka are being seriously affected due to anthropogenic pressure in the recent past. The changes of Dondra lagoon and its immediate surroundings were studied in conjunction with a GIS-coupled ecological survey and a questionnaire survey. The lagoon water surface area has decreased by about 0.92 ha (~8%) and the mangrove cover has increased by about 1.38 ha (~11%) over this period. The salinity of the lagoon has also reduced, forming a 'low saline' (3 psu) regime. About 40% of the lost water surface has scarified for a newly formed land mass (~0.4 ha) within the proximal part of the lagoon. The bridge, broken by the tsunami of 2004, has newly been constructed twice during the reporting period. The construction most likely led to impair the inflow and outflow through the lagoon mouth. Several development projects were launched in the immediate periphery of the lagoon stimulated soil erosion causing heavy siltation in the lagoon. The above changes in the morphometry of the lagoon is a cumulative effect of two factors; impaired inflow and outflow through the lagoon mouth, and the increase of the sediment input to the lagoon. If the ongoing processes are sustained, the lagoon will change into a different landscape. Therefore, early intervention to restore the lagoon hydrology is highly recommended if the lagoon ecosystem is to be protected.