Rapid sea level rise (SLR) represents a novel threat to mangroves, which could adapt through vertical accretion or landward expansion. Depending on tidal conditions and stressors, managers will likely have to intervene to enhance the adaptive capacity of mangroves. However, managers must be aware of, understand, and anticipate the risks of SLR-induced habitat degradation to plan adaptive measures, which must be supported by administrative resources, political will, and stakeholder engagement. Here, we studied how cognitive, experiential, and organizational factors influence risk awareness and adaptive management capacity of communal and state-based managers. In telephone-based interviews, the risk perception of 60 community-based and 23 governmental mangrove managers in Thailand was assessed to gain insights into their awareness and understanding of SLR risks, current management practices and adaptive measures, and the extent of their collaboration and stakeholder engagement. The findings show that most managers acknowledge the presence of SLR (72%) but perceived the adaptive capacity of mangroves as sufficiently high and the risk of SLR-induced degradation as minimal (63%), regardless of their affiliation. However, few respondents (18%) were aware that SLR would prolong hydroperiods and increase waterlogging stress of mangrove trees. The survey also revealed organization-specific biases. State officials cited a high level of uncertainty due to limited research and monitoring preventing them from planning adaptive measures. Community managers relied on their past experiences of mangrove recovery following disturbances, which might be unsuitable for informing management decisions in response to the novel threat of SLR. These findings indicate a lack of knowledge and guidelines for understanding and addressing SLR impacts. Additionally, there was an observed optimism bias among community managers, where past successful recoveries led to an overestimation of mangroves' adaptive capacity. Knowledge transfer and awareness-raising among mangrove resource stakeholders are critical for developing adaptation measures.