Leaf transport in mimic mangrove forests and seagrass beds

Mangrove forests and seagrass beds are thought to exchange particulate organic material, especially in the form of leaves. However, relatively little is known about the trapping capacity of mangrove above-ground roots and seagrass plants for leaf segments. We aimed to identify the major factors controlling the leaf-trapping capacity of mangroves and seagrasses in a flume study. For mangroves, we found that higher density mangrove roots enhanced trapping capacity whereas the presence of waves strongly reduced the trapping capacity. The latter might be explained by a reduced average collision time (i.e. the time a leaf was attached to a root structure) in the presence of waves. The ability for seagrass beds to trap leaves was dominated by the length/type of vegetation and the absence/presence of waves. Overall, our results suggest that mangroves-via their roots-have a more efficient trapping mechanism than seagrass beds. Mangrove roots extend through the entire water column the majority of the time, which enhances trapping capacity. In contrast, seagrass beds require particulate organic material to become entangled within the predominantly submerged shoots, making trapping dependent on the degraded state of the leaf and the water depth. Our results give an indication of parameters which could be used in a model of trapping capacity of these ecosystems. As leaves are associated with nutrients, we have identified factors which will help to determine what parameters affect the nutrient retention or export of ecosystems. These include density of roots, hydrodynamic conditions (absence/presence of waves), location of initial deposition, degradation stage and type of leaf.