Resumo

Mangroves are essential systems that provide valuable ecosystem services at the interface between land and sea in tropical and subtropical zones. However, they are currently at threat from anthropogenic activity, which have been shown to alter the diversity and composition of microbial communities associated with mangrove sediments. Here we present a study designed to characterize the bacterial diversity of mangrove sediments in 5 different locations in the State of Ceará, Northeast Brazil, which have been impacted by shrimp farming (COR and ACA), urbanization (CEA), river damming and evaporation (PAC) and we also included a pristine mangrove as a control (TIM). Samples from the bulk sediment and the root zones of Rhizophora mangle and Avicennia shaueriana were collected in 4 sampling expeditions, in the dry and wet seasons from two consecutive years. In total 300 samples were collected, extracted and 16S rRNA V4 amplified according to the Earth Microbiome Project standard protocols. As expected, overall Proteobacteria dominated the sediments, followed by Firmicutes, Chloroflexi, Acidobacteria and Actinobacteria. However, the river-damming mangrove (PAC) showed a predominance of Firmicutes, and a high abundance of the genus Psychrobacter. A vibrio bloom was detected during the year 2 wet season in a shrimp farm mangrove (COR). Microbial composition and betadiversity were significantly different between all mangroves, and between the bulk soil and root zone, except for the urbanized (CEA) and a shrimp farm location (COR). The pristine mangrove had an intermediate level of alpha diversity, while CEA and COR mangroves had the highest diversity and ACA and PAC mangroves had the lowest diversity. It is possible that in some levels of disturbance there is an increase in diversity and homogenization of the bacterial assemblies in mangrove sediments, however these results do indicate that disturbance impacts are probably multifactorial and complex.