When evaluating the robustness of our results, we found that even highly unfavorable assumptions regarding the cost of avoiding emissions would add only around $1 to the estimated per-ton cost (SI Appendix). An exception is when we approximate the opportunity cost for Indonesia and Thailand based solely on local estimates of potential returns from oil palm plantations (20) and shrimp mariculture (21, 22), respectively (SI Appendix). Assuming all mangroves in these countries face these pressures clearly overestimates the opportunity costs but nevertheless serves as a useful illustration. In this case, the supply curve shifts inward, such that in the high soil carbon case, the lower bound of the offset credit price ($10 ton−1 CO2) is met at around 60% of the total potential supply.