Litter Fall and Energy Flux in a Mangrove Ecosystem

Production, elemental composition andin situdecomposition of litter ofRhizophora apiculata,R. mucronata,Sonneratia albaandAvicenna officinaliswere studied in a mangrove ecosystem fringing Madovi–Zuari Estuaries on the Central West Coast of India. Litter yield ranged from 10.2 tonnes ha-1year-1inA. officinalisthrough 11.8 (R. apiculataandR. mucronata) to 17 tonnes ha-1year-1inS. alba. Seasonally maximum litter fall was in pre- and post-monsoon monthe, with the lowest production in the monsoon. Modelling of litter fall as a function of Julian day and six environmental parameters showed that the observed changes can be explained in terms of dry/wet season and wind speed, with a <10% fifference between calculated and observed annual changes. C, N and P contents of 13 litter fractions in the four species were 41.9–43.4, 0.66–1.15 and 0.054–0.105%. N:P, C:N and C:P ratios were <30, 30–100 and >1000. Total decomposition (98–100% loss in dry weight and C, and >90% loss in N and P) of yellow leaves was within 15 weeks in the twoRhizosporaspp. andS. alba, and within 8 weeks inA. officinalis. In all four species, mass changes during decomposition obeyed first-order kinetics. Comparison of C, N and P fluxes from the decomposing mangrove litter with phytoplankton, bacterial and secondary production in the estuarine waters showed that mangrove production is important mainly for the C budget of the Estuaries and in sustaining the microbial food chain and nutrient regeneration, rather than the particulate food chain directly.