Mangrove loss and degradation is increasingly due to climatic and environmental causes. In this study we investigate the two mangrove dieback events in two World Heritage Areas in north-west Australia; Ningaloo World Heritage Area (Mangrove Bay site) and Shark Bay World Heritage Area (Carnarvon site). Field (drone, and sediment cores), satellite and allometric equations were used to derive total biomass, sediment Corg stock and sequestration rates at the two study sites within impacted and unimpacted zones. We found that 33% of mangrove area has been lost in total. The Mangrove Bay impact event is related to El Niño Southern Oscillation (EÑSO), a cyclic climate phenomena, and has a lower Corg than Carnarvon, which we attribute the dieback occurrence to a major flood in the region that was then followed by a marine heatwave. We conclude that although global policy has increased to protect mangroves from reclamation, there needs to be greater interaction between terrestrial and marine management practices for mangroves which are at the marine and terrestrial interface, making them vulnerable to direct anthropogenic practices in both marine and terrestrial environments as well as climate changes.