1 Macrofaunal leaf consumption and degradation of leaves, woody twigs and r
oots were studied in mangrove island forests on a Belizean island. Factors
influencing accumulation of organic matter deposited both above and below g
round in this oligotrophic, autochothonous system were assessed.
2 Leaf degradation rates of Rhizophora mangle (red mangrove), Avicennia ger
minans (black mangrove) and Laguncularia racemosa (white mangrove) measured
in mesh bags, were much faster in the lower than the upper intertidal zone
. Mass loss was most rapid in A. germinans but zonal effects were much larg
er than species differences.
3 Exposure to invertebrates such as crabs and amphipods tripled overall rat
es of leaf litter breakdown. In the lower intertidal, crabs completely cons
umed some unbagged leaves within 23 days. Crabs also had an effect on some
upper intertidal sites, where degradation of leaves placed in artificial bu
rrows was 2.4 times faster than when placed on the soil surface.
4 In contrast to leaves (27 +/- 5% remaining after 230 days), roots and woo
dy twigs were highly refractory (40 +/- 2% and 51 +/- 6% remaining after 58
4 and 540 days, respectively). Root degradation did not vary by soil depth,
zone or species. Twigs of R. mangle and A. germinans degraded faster on th
e ground than in the canopy, whereas those of L. racemosa were highly resis
tant to decay regardless of position.
5 Peat formation at Twin Cays has occurred primarily through deposition and
slow turnover of mangrove roots, rather than above-ground tissues that are
either less abundant (woody twigs) or more readily removed (leaves).