Can mangroves keep pace with contemporary sea level rise? A global data review

Abstract

Coastal vegetated wetlands such as mangrove forests provide multiple ecosystem services, though are potentially threatened by contemporary accelerated sea level rise (SLR), in addition to other immediate threats such as agriculture and coastal development. Several studies have revealed that mangroves are able to adapt to, and keep pace with local relative SLR through vertical surface elevation change (SEC), however data are lacking, with often only surface accretion rate (SAR) data available. We systematically review published studies of SEC and SAR from globally distributed monitoring sites using meta-analysis, and compare them with the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5) SLR scenarios. Hydro-geomorphic setting plays an important role, with basin mangroves potentially less vulnerable to SLR through land building processes. We find that SAR in both basin and fringe mangroves can cope with low SLR scenario (RCP 2.6) throughout the 100 years projection period. However, SAR can only keep pace with high SLR scenario (RCP 8.5) up to year 2070 and 2055 in basin and fringe mangrove settings respectively. These were associated with potential sediment accumulation of 41 cm and 29 cm respectively from the baseline. Mangrove degradation promoted lowering trends of SEC, while mangrove management such as rehabilitation practice stimulated positive trends of SEC. Mangrove ecosystems may be vulnerable to contemporary SLR in small island locations such as the Caribbean, East Africa and parts of the Indo-Pacific that are dominated by fringe mangroves and where SEC cannot keep pace with both low and high IPCC AR5 SLR scenarios. A global expansion of current mangrove surface elevation monitoring effort is urgently needed in order to better assess the vulnerability of mangroves, and the factors affecting their resiliency in the face of rising sea levels.