90
these observations that in ecosystems dominated by slow-growing plants such as
trees, large, slowly decomposing detrital pools accumulate. Mangrove forest ecosystems are dominated by slow-growing trees growing on intertidal flats where the
soil is anoxic because it is constantly inundated by brackish water. Thus, mangrove
ecosystems satisfy the conditions for large necromass accumulation.
3.5.2.1 Necromass Increments and Decrements
Litter, such as leaves, flowers, twigs, and small branches, falls continuously in mangrove forests. According to Bouillon et al. (2008), litter input in mangrove forests
ranges from 4 to 13 t ha
−1
year
−1
by dry weight. They also reported a latitudinal difference in litter production, from an average of 10.4 t ha
−1
year
−1
(dry weight) at 0°
to 10° of latitude to an average of 4.7 t ha
−1
year
−1
(dry weight) at latitudes of >30°.
In the soil, plants continuously produce fine roots for nutrient and water uptake
and shed old roots. The production of root litter by mangrove plants is thought to be
considerable, so the organic matter content of mangrove soils may be high, but evaluation of root litter production is difficult. Thus, information on the mangrove necromass increment from dead roots is lacking. In addition to materials produced in the
mangrove ecosystem itself, litter may also be transported into the ecosystem from
surrounding areas. For example, leaves and branches may be carried from upland
areas by river flow, and materials from the sea such as algae, sea grasses, and dead
fish carried by waves and tidal currents can contribute further necromass. At the
same time, dead organic materials in mangrove ecosystems may be exported to
nearby waters (Gong and Ong 1990; Alongi et al. 1998). In fact, large masses of dead
wood from a mangrove forest are sometimes observed floating in the sea. The dead
materials remaining in mangrove ecosystems become fragmented by physical processes such as tidal fluctuations and wind, and by animal activities, and soluble
organic matter may be leached from the dead materials into the water. Cundell et al.
(1979) suggested that 30–50% of mangrove leaf biomass can be lost by leaching.
The leached compounds can serve as energy sources for organisms in the water. On
the floor of a mangrove forest, macrofauna (crabs, snails, mudskippers, prawns,
snakes, and so on) are often observed busily feeding on litter (Chong and Sasekumar
1981; Rodelli et al. 1984). Leaf-consuming crabs sometimes have carbon stable isotopic ratios, which can be used to trace carbon sources, close to the ratio of mangrove
litter, an indication that mangrove litter is their main food source. According to
Robertson et al. (1992), who compiled data on macrofaunal feeding in mangrove
forests, crabs consumed 28–71% of the litter in mangrove forests. Moreover, various
prawn species that live in mangrove waterways also feed on dead organic materials
derived from mangrove plants (Chong and Sasekumar 1981; Rodelli et al. 1984;
Chong et al. 2001). The species that feed on the litter and the intensity of their feeding depend on factors such the macrofaunal species composition and physicochemical conditions in the forest. At smaller scales, bacteria and fungi are major
decomposers in mangrove ecosystems. These organisms extract electrons from
organic materials in the soil and obtain energy from the electron flow for their
T. Inoue
these observations that in ecosystems dominated by slow-growing plants such as
trees, large, slowly decomposing detrital pools accumulate. Mangrove forest ecosystems are dominated by slow-growing trees growing on intertidal flats where the
soil is anoxic because it is constantly inundated by brackish water. Thus, mangrove
ecosystems satisfy the conditions for large necromass accumulation.
3.5.2.1 Necromass Increments and Decrements
Litter, such as leaves, flowers, twigs, and small branches, falls continuously in mangrove forests. According to Bouillon et al. (2008), litter input in mangrove forests
ranges from 4 to 13 t ha
−1
year
−1
by dry weight. They also reported a latitudinal difference in litter production, from an average of 10.4 t ha
−1
year
−1
(dry weight) at 0°
to 10° of latitude to an average of 4.7 t ha
−1
year
−1
(dry weight) at latitudes of >30°.
In the soil, plants continuously produce fine roots for nutrient and water uptake
and shed old roots. The production of root litter by mangrove plants is thought to be
considerable, so the organic matter content of mangrove soils may be high, but evaluation of root litter production is difficult. Thus, information on the mangrove necromass increment from dead roots is lacking. In addition to materials produced in the
mangrove ecosystem itself, litter may also be transported into the ecosystem from
surrounding areas. For example, leaves and branches may be carried from upland
areas by river flow, and materials from the sea such as algae, sea grasses, and dead
fish carried by waves and tidal currents can contribute further necromass. At the
same time, dead organic materials in mangrove ecosystems may be exported to
nearby waters (Gong and Ong 1990; Alongi et al. 1998). In fact, large masses of dead
wood from a mangrove forest are sometimes observed floating in the sea. The dead
materials remaining in mangrove ecosystems become fragmented by physical processes such as tidal fluctuations and wind, and by animal activities, and soluble
organic matter may be leached from the dead materials into the water. Cundell et al.
(1979) suggested that 30–50% of mangrove leaf biomass can be lost by leaching.
The leached compounds can serve as energy sources for organisms in the water. On
the floor of a mangrove forest, macrofauna (crabs, snails, mudskippers, prawns,
snakes, and so on) are often observed busily feeding on litter (Chong and Sasekumar
1981; Rodelli et al. 1984). Leaf-consuming crabs sometimes have carbon stable isotopic ratios, which can be used to trace carbon sources, close to the ratio of mangrove
litter, an indication that mangrove litter is their main food source. According to
Robertson et al. (1992), who compiled data on macrofaunal feeding in mangrove
forests, crabs consumed 28–71% of the litter in mangrove forests. Moreover, various
prawn species that live in mangrove waterways also feed on dead organic materials
derived from mangrove plants (Chong and Sasekumar 1981; Rodelli et al. 1984;
Chong et al. 2001). The species that feed on the litter and the intensity of their feeding depend on factors such the macrofaunal species composition and physicochemical conditions in the forest. At smaller scales, bacteria and fungi are major
decomposers in mangrove ecosystems. These organisms extract electrons from
organic materials in the soil and obtain energy from the electron flow for their
T. Inoue