Litterfall and decomposition of Rhizophora mangle L. in a coastal lagoon in the southern Gulf of Mexico

The dynamics of Rhizophora mangle litter production and decomposition were studied in a tropical coastal lagoon on the Gulf of Mexico in Veracruz, Mexico over a year (October 2002-October 2003). This region is characterized by three seasons: northerly winds (called 'nortes'), dry, and rainy. Annual litter production (1116 g m^sup -2^) followed a seasonal pattern with leaf litter as the main fraction (70%) with two peaks in the dry and one in the rainy season. Leaf decomposition was evaluated with two types of litter bag in each season: fine mesh (1×1 mm) and coarse mesh (3×7 mm). Decomposition data were adjusted to a single negative exponential model. The results indicated faster decomposition rates in the coarse litter bag and significant differences among seasons. However these differences occurred after the 60th day of decomposition, indicating that leaching and microbial action were responsible for more than 50% of mass loss. After this period, the effects of aquatic invertebrates were evident but depended on climatic conditions. In the rainy season, the gastropod Neritina reclivata was associated with increasing leaf decomposition rate. In the 'nortes' season, the effect of aquatic invertebrates was smaller, and there were no differences in the decay constants calculated for the two litter bag types. High litter production represents an important input of organic matter which, through decomposition, may represent an important source of C, N, and P in this aquatic system.[PUBLICATION ABSTRACT]