Despite the expected importance, the changes in mangrove ecosystems and the main causes in Fiji have not been well addressed. To address the issues, we collected data from multiple sources to assess mangrove ecosystem variation due to both natural factors and human impacts in the Ba and Rewa deltas, Fiji. Landsat satellite data were used to map the land use and cover of the study area from 2000 to 2020. Questionnaire surveys were conducted to identify the main uses of mangroves that could influence mangrove ecosystems. Over the period investigated, the mangrove area increased by 572 ha (by 12%) in Ba and decreased by 697 ha (by 9%) in Rewa. The social survey revealed that 45% of respondents in the Ba delta and 20% in the Rewa delta visited the mangrove area daily in search of food resources. The net annual economic loss and lost functioning of mangroves as an anthropogenic CO 2 reservoir caused by mangrove degradation in the two deltas were estimated to be 335,000 USD and 202 t-C, respectively. Because local livelihoods are strongly linked with mangroves, the outcomes of this study will provide preliminary information for policy interventions to ensure the sustainability of the mangrove ecosystem.