Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems—marshes, mangroves, and seagrasses—that may be lost with habitat destruction (‘conversion’). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this ‘blue carbon’ can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15–1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3–19% of those from deforestation globally, and result in economic damages of $US 6–42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of land-use conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the well-recognized ecosystem services of coastal habitats.

The international scientific community is increasingly recognizing the role of natural systems in climate‐change mitigation. While forests have historically been the primary focus of such efforts, coastal wetlands – particularly seagrasses, tidal marshes, and mangroves – are now considered important and effective long‐term carbon sinks. However, some members of the coastal and marine policy and management community have been interested in expanding climate mitigation strategies to include other components within coastal and marine systems, such as coral reefs, phytoplankton, kelp forests, and marine fauna. We analyze the scientific evidence regarding whether these marine ecosystems and ecosystem components are viable long‐term carbon sinks and whether they can be managed for climate mitigation. Our findings could assist decision makers and conservation practitioners in identifying which components of coastal and marine ecosystems should be prioritized in current climate mitigation strategies and policies.

Changing environments and resource demands present challenges to Antarctic conservation.

The global significance of carbon storage in Indonesia's coastal wetlands was assessed based on published and unpublished measurements of the organic carbon content of living seagrass and mangrove biomass and soil pools. For seagrasses, median above-and below-ground biomass was 0.29 and 1.13 Mg C ha -1 respectively; the median soil pool was 118.1 Mg C ha -1 . Combining plant biomass and soil, median carbon storage in an Indonesian seagrass meadow is 119.5 Mg C ha -1 . Extrapolated to the estimated total seagrass area of 30,000 km 2 , the national storage value is 368.5 Tg C. For mangroves, median above-and below-ground biomass was 159.1 and 16.7 Mg C ha -1 , respectively; the median soil pool was 774.7 Mg C ha -1 . The median carbon storage in an Indonesian mangrove forest is 950.5 Mg C ha -1 . Extrapolated to the total estimated mangrove area of 31,894 km 2 , the national storage value is 3.0 Pg C, a likely underestimate if these habitats sequester carbon at soil depths [1 m and/or sequester inorganic carbon. Together, Indonesia's seagrasses and mangroves conservatively account for 3.4 Pg C, roughly 17 % of the world's blue carbon reservoir. Continued degradation and destruction of these wetlands has important consequences for CO 2 emissions and dissolved carbon exchange with adjacent coastal waters. We estimate that roughly 29,040 Gg CO 2 (eq.) is returned annually to the atmosphere-ocean pool. This amount is equivalent to about 3.2 % of Indonesia's annual emissions associated with forest and peat land conversion. These results highlight the urgent need for blue carbon and REDD? projects as a means to stem the decline in wetland area and to mitigate the release of a significant fraction of the world's coastal carbon stores.

Ocean acidification has emerged over the last two decades as one of the largest threats to marine organisms and ecosystems. However, most research efforts on ocean acidification have so far neglected management and related policy issues to focus instead on understanding its ecological and biogeochemical implications. This shortfall is addressed here with a systematic, international and critical review of management and policy options. In particular, we investigate the assumption that fighting acidification is mainly, but not only, about reducing CO 2 emissions, and explore the leeway that this emerging problem may open in old environmental issues. We review nine types of management responses, initially grouped under four categories: preventing ocean acidification; strengthening ecosystem resilience; adapting human activities; and repairing damages. Connecting and comparing options leads to classifying them, in a qualitative way, according to their potential and feasibility. While reducing CO 2 emissions is confirmed as the key action that must be taken against acidification, some of the other options appear to have the potential to buy time, e.g. by relieving the pressure of other stressors, and help marine life face unavoidable acidification. Although the existing legal basis to take action shows few gaps, policy challenges are significant: tackling them will mean succeeding in various areas of environmental management where we failed to a large extent so far.