LITTER DYNAMICS IN RIVERINE MANGROVE FORESTS IN THE GUAYAS RIVER ESTUARY, ECUADOR

The hypothesis that rates of litter turnover in mangroves are controll ed by local geophysical processes such as tides has been studied at si tes with mostly small tides (< 1 m) and minor crab consumption of leaf litter. Our study describes litter dynamics of three riverine mangrov e sites (M1, M2, M3), inhabited by the mangrove crab Ucides occidental is, located in a macrotidal (> 3 m) river-dominated tropical estuary i n Ecuador (2.5 degrees S latitude). There were statistical effects of site and depth on soil salinities, but ail mean salinities were < 17 g kg(-1). Dairy rates of leaf litter fall were higher in the rainy comp ared to the dry season, although no seasonal effects were observed for other components of litter fall. Annual total litter fall rates were significantly different among sites at 10.64, 6.47, and 7.87 Mg ha(-1) year(-1) for M1, M2, and M3, respectively. There were significant sit e (M3 > M2 > M1) and season (rainy > dry) effects on leaf degradation, and both effects were related to differences in the initial nitrogen content of senescent leaves. Mean leaf litter standing crop among the sites ranged from 1.53 to 9.18 g m(-2), but amounts were strongly seas onal with peak values during September in both years of our study (no significant year effect) at all three sites. Leaf turnover rates based on leaf fall estimates and litter standing crop were 10- to 20-fold h igher than estimated from rates of leaf degradation, indicating the si gnificant effect of leaf transport by tides and crabs. Field experimen ts demonstrated that the mangrove crab can remove daily additions of l eaf material within 1 h at all three sites, except during August-Octob er, when the crab is inactive on the forest floor. Even though there i s seasonally elevated leaf accumulation on the forest floor during thi s time, leaf turnover rates are much higher than expected based on lea f degradation, demonstrating the importance of tidal export. This is t he first description of how crabs influence litter dynamics in the New World tropics, and results are similar to higher rates of crab transp ort of leaf litter in the Old World tropics. Even in riverine mangrove s with high geophysical energies, patterns of litter dynamics can be i nfluenced by ecological processes such as crab transport.