LITTER FALL AND ENERGY FLUX IN A MANGROVE ECOSYSTEM

Production, elemental composition and in situ decomposition of litter of Rhizophora apiculata, R. mucronata, Sonneratia alba and Avicennia o fficinalis were studied in a mangrove ecosystem fringing Mandovi-Zuari Estuaries on the Central West Coast of India. Litter yield ranged fro m 10.2 tonnes ha(-1) year(-1) in A. officinalis through 11.8 (R. apicu lata and R. mucronata) to 17 tonnes ha(-1) year(-1) in S. alba. Season ally maximum litter fall was in pre- and post-monsoon months, with the lowest production in the monsoon. Modelling of litter fall as a funct ion of Julian day and six environmental parameters showed that the obs erved changes can be explained in terms of dry/wet season and wind spe ed, with a <10% difference between calculated and observed annual aver ages. C, N and P contents of 13 litter fractions in the four species w ere 41.9-43.4, 0.66-1.15 and 0.054-0.105%. N:P, C:N and C:P ratios wer e <30, 30-100 and >1000. Total decomposition (98-100% loss in dry weig ht and C, and >90% loss in N and P) of yellow leaves was within 15 wee ks in the two Rhizophora spp. and S. alba, and within 8 weeks in A. of ficinalis. Ln all four species, mass changes during decomposition obey ed first-order kinetics. Comparison of C, N and P fluxes from the deco mposing mangrove litter with phytoplankton, bacterial and secondary pr oduction in the estuarine waters showed that mangrove production is im portant mainly for the C budget of the Estuaries and in sustaining the microbial food chain and nutrient regeneration, rather than the parti culate food chain directly. (C) 1997 Academic Press Limited.