Litter fall and decomposition of mangrove species Avicennia marina and Rhizophora mucronata in Maputo Bay, Mozambique

Abstract

Litter fall and decomposition of mangrove leaves were compared for different seasons, species (Avicennia marina and Rhizophora mucronata) and sites in southern Mozambique. Mangrove leaf litter fall and decomposition was estimated using small mesh collecting-baskets and litter bags respectively in 2006 and 2007 at two sites of Maputo Bay: an urban dwarf mangrove at Costa do Sol (Maputo City) and a rural well-developed mangrove at Saco (Inhaca Island). A. marina at Saco produced more litter (dry season 10.6 g m-2 and wet season 14.2 g m-2) than R. mucronata (dry season 4.6 g m-2 and wet season 14.1 g m-2), and leaves contributed more to total litter fall in the dry season (February/March) compared with the wet season (September/October) for both species. Decomposition by means of loss of ash free dry weight (AFDW) from leaves maintained in the subtidal was best described by double exponential models which showed loss rates of leaves along the time. Field experiments at Saco showed that submerged leaves of A. marina decomposed faster than R. mucronata. For A. marina, the average time required to lose half of the initial AFDW (t 0,5) was 96 days and 78 days for the dry and wet season respectively, whereas for R. mucronata leaves it took 151 days in the dry and 476 days in the wet season. At Costa do Sol, A. marina leaves took 171 and 48 days for the dry and wet seasons respectively to lose half AFDW; whereas R. mucronata took 98 days in the dry and 25 days in the wet season. The results showed that breakdown of leaf litter was season and species dependent. Litter decomposition in the wet season was faster than the dry season and A. marina had the fastest decomposition rates, appearing to act as a principle pioneer species for enrichment of the fringing mangrove habitats of subtropical eastern Africa.