The role of bioturbation by Ucides cordatus crab in the fractionation and bioavailability of trace metals in tropical semiarid mangroves

•U. cordatus burrowing activity affect mangrove soils biogeochemical conditions.•The bioturbation decreases the role of pyrite as a trace metal sink.•As pyrite decreases, the participation of iron oxy-hydroxides increases.•Bioturbation increases trace metals bioavailability and bioaccumulation.•Metals contents in the crab tissues is a good proxy to evaluate its bioavailability.

This study evaluated the burrowing activity of U. cordatus and its effects on Fe, Cu and Zn fractionation, bioavailability and bioaccumulation in a semiarid mangrove area (Ceará state, NE-Brazil). Were analyzed the Eh; pH; grain size and pore water composition; total S and organic C, and the speciation of Fe, Cu and Zn solid-phases in two areas: a densely populated crab and a control site. The burrowing activity and seasonal variation affect the biogeochemical conditions of mangrove soils increasing metals bioavailability and bioaccumulation. The crab burrows favors the entrance of oxygen into the soil, oxidizing the pyrite and forming poorly-crystalline Fe minerals, increasing the risks of biocontamination. Furthermore, the metals content in the hepatopancreas are a good proxy for the evaluation of bioavailable metal forms and, thus, further studies must be conducted in order to evaluate the potential use of U. cordatus as a bioindicator for trace metals contamination.