Mangrove forests are highly productive yet vulnerable ecosystems that act as important carbon sinks ("blue carbon"). The objective of this work was to analyze the impact of anthropogenic activities on microbiome structure and functioning. The metagenomic analysis revealed that the taxonomic compositions were grossly similar across all mangrove microbiomes. Remarkably, these microbiomes, along the gradient of anthropogenic impact, showed fluctuations in the relative abundances of bacterial taxa predicted to be involved in sulfur cycling processes. Functions involved in sulfur metabolism, such as APS pathways (associated with sulfate reduction and sulfur oxidation processes) were prevalent across the microbiomes, being sox and dsrAB genes highly expressed on anthropogenically-impacted areas. Apparently, the oil-impacted microbiomes were more affected in taxonomic than in functional terms, as high functional redundancies were noted across them. The microbial gene diversity found was typical for a functional system, even following the previous disturbance.