Mangrove leaf transportation: Do mimic Avicennia and Rhizophora roots retain or donate leaves?

Mangrove forests are typically located in the catchment areas of the terrestrial zone and can be adjacent to oceanic ecosystems (e.g. seagrass beds and coral reefs). These forests are thought to provide ecosystem services by retaining particulate organic matter such as detrital leaves that can facilitate nutrient-sensitive seagrass beds and coral reefs. However, there is a scarcity of knowledge about the mechanisms that control leaf retention. In this study, using a flume and mimic mangrove roots, we aimed to identify the physical (hydrodynamics, root density and type) and biological (size and decay state of the leaf) parameters that control the retention of leaves within these mangrove forests. Our study found that the majority (83 to 92%) of decaying leaves were retained within Rhizophora and Avicennia mimic roots. Only the mimic Rhizophora roots trapped fresh fragmented leaves (25%); other drivers such as fragment size, root density and presence of waves showed a significant difference in trapping leaves. These results suggest that the zonation of tree species and the hydrodynamics acting on roots can play an important role in the leaf-trapping capacity of a mangrove forest. This information may be used in planning for conservation and restoration of these forests, especially with respect to facilitating the establishment and expansion of connected ecosystems. However, further work in the field under more realistic hydrodynamic conditions is needed to verify the results of this flume experiment.