Leaf litter and its breakdown products represent an important input of organic matter and nutrients to mangrove sediments and adjacent coastal ecosystems. It is commonly assumed that old-grown stands with mature trees contribute more to the permanent sediment organic matter pool than younger stands. However, neither are interspecific differences in leaf decay rates taken into account in this assumption nor is our understanding of the underlying mechanisms or drivers of differences in leaf chemistry sufficient. This study examines the influence of different plant species and ontogenetic stage on the microbial decay of mangrove leaf litter. A litterbag experiment was conducted in the Matang Mangrove Forest Reserve, Malaysia, to monitor leaf litter mass loss, and changes in leaf litter chemistry and microbial enzyme activity. Four mangrove species of different morphologies were selected, namely the trees Rhizophora apiculata and Bruguiera parviflora, the fern Acrostichum aureum and the shrub Acanthus ilicifolius. Decay rates of mangrove leaf litter decreased from A. ilicifolius to R. apiculata to B. parviflora to A. aureum. Leaf litter mass, total phenolic content, protein precipitation capacity and phenol oxidase activity were found to decline rapidly during the early stage of decay. Leaf litter from immature plants differed from that of mature plants in total phenolic content, phenolic signature, protein precipitating capacity and protease activity. For R. apiculata, but not of the other species, leaf litter from immature plants decayed faster than the litter of mature plants. The findings of this study advance our understanding of the organic matter dynamics in mangrove stands of different compositions and ages and will, thus, prove useful in mangrove forest management.
Generic global conservation targets lack the ambition required for certain habitats of critical value for biodiversity and human well-being. Developing more challenging targets for such habitats may offer a solution. Mangrove forests provide an example: any and all future loss will have negative repercussions, while many impacts could be reversed through extensive restoration. The Global Mangrove Alliance, an international grouping of 100 civil society and academic partners, has set goals to halt anthropogenic losses, accelerate restoration and greatly enhance protection by 2030. Using global-scale data, we estimate that achieving these goals will avoid losses of some 1500 km2; restore some 4000 km2; and secure an additional 36 000 km2 of mangroves under effective and equitable protection. Multiple benefits will follow, and we present values for carbon storage gains and avoided losses. Global datasets can guide broad approaches, while quantifying the challenges and benefits provides inspiration and impetus for change.