DECOMPOSITION DYNAMICS OF LITTERFALL IN MANGROVE ECOSYSTEMS

Litterfall decomposition is a vital ecological process in tropical forests, shaping nutrient cycling and carbon dynamics. In mangrove ecosystems, accumulated leaf litter will decompose to form peat under certain environmental conditions, and the rate of decomposition can regulate the formation of in-situ leaf mats. Further, the breakdown of leaf litter is significantly influenced by invertebrate detritivores. Among them, the coffee bean snail (Melampus coffea L.) is a macroinvertebrate detritivore (> 1 mm) that has been recognized to play a crucial role in litterfall decomposition within mangroves. This study investigates decomposition rates of red mangrove (Rhizophora mangle L.) leaves and leaf mat formation in contrasting mangrove sites along a hydrological gradient in South Florida without the interference of macroinvertebrate detritivory. To estimate litterfall decomposition rates, litterbags containing red mangrove leaves were deployed and collected at regular intervals throughout the year. Linear regressions were used to compare the percentages of organic mass remaining in surficial and subsurface litterbags. The population densities of M. coffea were censused to evaluate their correlation with intact leaf mats. Contrary to expectations, this study found no significant difference in M. coffea populations or leaf litter decomposition rates between sites. However, leaf mats were observed in inundated, interior basin mangroves where nearly continuous flooding excludes M. coffea from the leaf litter whereas leaf mats were not observed in fringe mangroves where litterfall experiences tidal export and rapid consumption by M. coffea during low tides. These data suggest a correlation between the presence of intact leaf mats and the access of pulmonate macroinvertebrate detritivores to the leaf litter layer. The results support that macroinvertebrate detritivores, particularly M. coffea, play a crucial role in shaping litterfall decomposition in mangroves, and their restricted access to litterfall in basin mangroves promotes the formation of leaf mats in these coastal environments. In tropical freshwater peatlands, localized leaf mats may accumulate in pools caused by tree falls where flooding decreases the decomposition rate of leaf litter; these depositional settings are comparable to inundated swales observed in modern basin mangroves.