Mangrove ecosystems play a big role in the carbon cycle of tropical coastal areas. Scientists have been studying how organic matter moves through these ecosystems using stable isotopes. They found that different sources contribute to the carbon in mangroves, and that microbes and animals use this carbon in different ways. The exchange of organic matter between mangroves and nearby ecosystems is also important. Stable isotopes have helped challenge old ideas and show the need to understand where the carbon comes from in these dynamic environments. Future studies should combine different methods to better track organic matter sources.