Climate change-driven dieback triggers metal mobilization in mangroves: a case study from the Maldives

Mangrove ecosystems play a vital role in mitigating trace metal pollution by acting as natural biofilters that trap and accumulate trace metals from surrounding sediments. However, climate change-induced stressors, such as sea level rise and salinity fluctuations, can disrupt their regulatory capacity. In March 2020, a large-scale dieback of Bruguiera cylindrica in northern Maldives occurred, attributed to extreme climatic conditions, sea level rise, and enhanced salinity. This study examines the variability of 8 trace metals in sediments and plant tissues across dieback and non-dieback zones, assessing the impact of climate change on metal bioavailability and accumulation. Sediment analysis revealed consistently higher metal concentrations in non-dieback zones, reflecting enhanced sediment retention by healthy stands, while dieback sites exhibited erosion and flushing of metals due to altered hydrodynamics. Pollution load and geoaccumulation indices indicated moderate to very high contamination, particularly for Cd, often linked to agricultural runoff and local anthropogenic inputs. Bruguiera cylindrica in dieback areas exhibited elevated metal uptake, particularly Cu and Cd, while non-dieback sites showed below-detection levels, suggesting stress-enhanced uptake and translocation of bioavailable metals. These findings revealed that climate-induced mangrove mortality not only weakens the sedimentary sink function but may also increase metal export and toxicity risks to adjacent marine systems. Large-scale dieback events in the Maldives parallel observations from Australia and Brazil, underscoring the global vulnerability of mangroves to climate extremes. For island nations, these results highlight the urgency of integrated strategies to mitigate climate impacts, regulate metal inputs, and restore mangrove resilience as critical defenses against coastal degradation and pollution.