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

Abstract

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