This work presents the phytosociological characteristics of Todos os Santos Bay mangrove communities in Brazil as well as the chemical composition of the leaves of the three mangrove species and their associated sediment. For the qualitative, phytosociological investigation, the contiguous parcel method was used at five sites associated with petroleum extraction (Site 4, Fontes Island), transportation (Site 2, Madre de Deus and 3, Pati Island), and refining (Site 1, Mataripe). Each site was divided into seven 10 x 10 m parcels. Results indicated that the Todos os Santos mangrove ecosystem has a fringe physiognomy with low bearing, containing the obligate species, Laguncularia racemosa, Rhizophora mangle, and Avicennia schaueriana, the former being the dominant species. The sediment presented a predominantly sandy texture and the average levels of the elements P, Ca, K, Mg, Na, Cu, Zn, Mn, and Fe were within the normal range of variation for this kind of environment. The chemical analysis of leaves revealed significant differences among the species, although Rhizophora mangle and Laguncularia racemosa demonstrated a great similarity in their average concentrations of the minerals N, P, K. Ca, Mg, S, Cu, Fe, Mn, and Zn. For the three species, the individuals collected at Mataripe (Site 1) site, presented significantly higher (p<0.05) concentration of the elements N, P,and Cu, when compared to the others sites, thus suggesting the influence of the oil refinery on mangrove plants.

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