Decay of Rhizophora apiculata (Blume) and Xylocarpus granatum (Koenig) detrital sources in the Sarawak Mangrove, Malaysia

Decaying mangrove detritus plays a significant role in nutrient cycling and fueling in both the forests and aquatic habitats where the detritus stems from estuarine and coastal food webs. Detrital decay rates partly depend on the type of detritus, but most studies have thus far focused on leaf litter decay and decomposition, whereas other detrital sources (except for roots) have largely been ignored. We compare the decay rates of Rhizophora apiculata and Xylocarpus granatum non-leafy detritus (flowers, propagules, stipules, and twigs) with mangrove leaf litter in field studies, using litter bags during the dry and the wet seasons in the tropical mangrove forest of Sibuti, Sarawak, Malaysia. We observed higher microbial decay rates of stipules, flowers, propagules, and twigs for both the R. apiculata and X. granatumduring the wet months. By contrast, leaf decay rates were higher during the dry months. Decay rates depended on the lignin content of the detrital sources of both species, both during dry and wet months. Accordingly, the half-life (T-0.5) and 95% lifespan (T-0.95) of non-leaf materials (flowers, propagules, stipules and twigs) for both species were remarkably longer than those of leaf litter. Slowly decaying non-leafy detritus may play a significant role in nutrient and carbon cycling over longer time, when leaf litter is either being decomposing rapidly and/or being washed away by tidal flush and river runoff. Hence, non-leafy (flowers, propagules, stipules and twigs) detritus should be taken into account when budgeting organic matter turnover in mangroves.