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Coastal tidal wetlands produce and accumulate significant amounts of organic carbon (C) that help to mitigate climate change. However, previous data limitations have prevented a robust evaluation of the global rates and mechanisms driving C accumulation. Here, we go beyond recent soil C stock estimates to reveal global tidal wetland C accumulation and predict changes under relative sea-level rise, temperature and precipitation. We use data from literature study sites and our new observations spanning wide latitudinal gradients and 20 countries. Globally, tidal wetlands accumulate 53.65 (95%CI: 48.52–59.01) Tg C yr−1, which is ∼30% of the organic C buried on the ocean floor. Modelling based on current climatic drivers and under projected emissions scenarios revealed a net increase in the global C accumulation by 2100. This rapid increase is driven by sea-level rise in tidal marshes, and higher temperature and precipitation in mangroves. Countries with large areas of coastal wetlands, like Indonesia and Mexico, are more susceptible to tidal wetland C losses under climate change, while regions such as Australia, Brazil, the USA and China will experience a significant C accumulation increase under all projected scenarios.

After its introduction into North America, Euro-Asian Phragmites australis became an aggressive invasive wetland grass along the Atlantic coast of North America. Its distribution range has since expanded to the middle, south and southwest of North America, where invasive P. australis has replaced millions of hectares of native plants in inland and tidal wetlands. Another P. australis invasion from the Mediterranean region is simultaneously occurring in the Gulf region of the United States and some countries in South America. Here, we analysed the occurrence records of the two Old World invasive lineages of P. australis (Haplotype M and Med) in both their native and introduced ranges using environmental niche models (ENMs) to assess (i) whether a niche shift accompanied the invasions in the New World; (ii) the role of biologically relevant climatic variables and human influence in the process of invasion; and (iii) the current potential distribution of these two lineages. We detected local niche shifts along the East Coast of North America and the Gulf Coast of the United States for Haplotype M and around the Mississippi Delta and Florida of the United States for Med. The new niche of the introduced Haplotype M accounts for temperature fluctuations and increased precipitation. The introduced Med lineage has enlarged its original subtropical niche to the tropics-subtropics, invading regions with a high annual mean temperature (> ca. 10 °C) and high precipitation in the driest period. Human influence is an important factor for both niches. We suggest that an increase in precipitation in the 20th century, global warming and human-made habitats have shaped the invasive niches of the two lineages in the New World. However, as the invasions are ongoing and human and natural disturbances occur concomitantly, the future distribution ranges of the two lineages may diverge from the potential distribution ranges detected in this study.

Coastal wetlands mainly include ecosystems of mangroves, coral reefs, salt marsh, and sea grass beds. As the buffer zone between land and sea, they are frequently threatened from both sides. The world coastal wetland lost more than 50% of its area in the 20th century, largely before their great value, such as wave attenuation, erosion control, biodiversity support, and carbon sequestration, was fully recognized. World wetland loss and degradation was accelerated in the last three decades, caused by both anthropogenic and natural factors, such as land reclamation, aquaculture, urbanization, harbor and navigation channel construction, decreased sediment input from the catchments, sea level rise, and erosion. Aquaculture is one of the key destinations of coastal wetland transformation. Profound consequences have been caused by coastal wetland loss, such as habitat loss for wild species, CO 2 and N 2 O emission from land reclamation and aquaculture, and flooding. Great efforts have been made to restore coastal wetlands, but challenges remain due to lack of knowledge about interactions between vegetation and morphological dynamics. Compromise among the different functionalities remains a challenge during restoration of coastal wetlands, especially when faced with highly profitable coastal land use. To solve the problem, multi-disciplinary efforts are needed from physio-chemical-biological monitoring to modelling, designing, and restoring practices with site-specific knowledge.