Due to human activities atmospheric carbon dioxide concentrations have increased from 280 to almost 400 parts per million since the industrial revolution. This has resulted in global warming and a sea surface temperature increase of approximately 0.7 degrees Celsius. About half of the excess carbon is now dissolved in the oceans, leading to a 30 % increase in ocean water acidity. Warming and acidification combined have potentially disastrous consequences for coral reefs if the current carbon dioxide emission trend continues. In tropical Southeast Asia several species of seagrasses can often be found growing together on reef flats where they form dense meadows. Seagrasses have the potential to mitigate the effects of global warming on coral reefs by taking up carbon and increasing seawater pH. They also accumulate organic matter with a high residence time in below-ground deposits, thereby taking carbon out of the global cycle for extended periods of time. However, most of what is known about tropical seagrasses stems from research conducted in the Caribbean or Australia. A series of experiments and studies is planned in collaboration between the Alfred-Wegener-Institute for Polar and Marine Research, Germany, and the Research and Development Center for Marine, Coastal and Small Islands (RDC MacSI) of Hasanuddin University Makassar, Indonesia. The studies will be conducted in the Spermonde Archipelago, Makassar Strait, Indonesia. Dissolved carbon dioxide concentrations will be elevated in in-situ mesocosms to study the reaction of tropical seagrasses to the concentrations expected in the year 2100. Sediment organic content will be determined in soil and sediment cores collected in a variety of seagrass habitats, ranging from “river estuary / mud flats” over “shallow coastal and back reef / coral reef” to “deep water / deep costal / fore reef”. The results will be compared to nearby mangrove and bare sand areas.