Leaf litter processing by macrodetritivores in natural and restored Neotropical mangrove forests

Knowledge of mangrove litter dynamics is crucial to an understanding of the energetic links between mangrove ecosystems and nearby estuaries and coastal waters. Previous research into the role played by macrodetritivores in Neotropical mangrove litter processing has been contradictory. This study used leaf tethering to examine the effects of macrodetritivores on initial rates of mangrove litter degradation in South Florida, USA. Leaf litter dynamics experiments were run in both natural and restored mangrove forests to assess functionality of the restoration projects. Although less important than in some other parts of the world (e.g., the Indo-Pacific), macrodetritivores played a significant role in increasing in situ leaf degradation within mangrove forests on both east and west coasts of Florida. In contrast to Indo-Pacific forests, gastropods were the primary macrodetritivores usually observed feeding on abscised mangrove leaves in South Florida. During leaf tethering trials, macrodetritivores (the gastropod Melampus coffeus and grapsid crabs) attacked between 1.7 and 29.6% of deployed leaves at different sites and accounted for 24.0% more leaf mass loss compared to non-attacked leaves. Macrodetritivores increased leaf litter degradation in several different mangrove forest types and under different environmental conditions within this study. In addition, macrodetritivore degradation rates varied among site histories (natural versus restored) and macrodetritivore characteristics. Although macrodetritivore community populations were greater in restored forests, litter cycling processes were similar to nearby reference forests. Litter and environmental characteristics were also examined to help understand macrodetritivore impacts on litter cycling. Litter fall rates varied from 0.4 ± 0.1 to 3.2 ± 0.3 g m-2 d-1 at the several sites. Standing stocks of litter on the forest floor varied widely within and among sites and ranged from 29 g m-2 to 559 g m-2 with an overall mean of 269 g m-2. Differences in litter fall and litter standing crop across sites and seasons were partly attributable to environmental variables (i.e., temperature, porewater salinity, forest structure, and light). The restored mangrove forests observed during this study appear to have gained some natural functionality of leaf litter dynamics as compared to nearby reference forests