A role of a herbivorous crab, Neosarmatium smithi, in dissolved iron elution from mangrove ecosystems

Iron solubilization in mangrove soils associated with polyphenols leached out from leaf-litter can improve iron bioavailability. In this context, the leaf-removing process by mangrove crabs would increase reacting frequency of the polyphenols in mangrove leaves with iron in the soils. In this study, we investigated ecological roles of a leaf-removing crab, Neosarmatium smithi , on the iron solubilization process. After the fallen leaves carried by the crabs to their burrows and eaten by them, polyphenols may be remained in their feces. If so, contact of polyphenols in the feces with mangrove soils could promote elution of dissolved iron from the soils. In order to demonstrate this hypothesis, we firstly surveyed the appearance ratio of the black part in crab burrows and measured total phenolic content in feces of N. smithi as well as in the black part soil. Then, we examined influences of the crab feces on dissolved iron elution from mangrove soils. As the results, the appearance ratio of the black part in the burrow was 67 % and the phenolic content in the feces, the black part, and the yellow part in crab burrows were 9.93, 0.49, and 0.12 mg g − 1 , respectively. Dissolved iron content in the solution (soil ＋ water extract from feces) was 0.65 μ g g − 1 and this content was 4.5 times higher than the control (soil ＋ distilled water). We suggest that the polyphenols remained in the feces affect to solubilize insoluble forms of iron by iron reduction and chelating properties.