The effects of mining tailings in the physiology of benthic algae: understanding the relation between mud’s inductive acidification and the heavy metal’s toxicity

•Mariana’s mud was evaluated for toxic effects of heavy metals and acidification.•Sargassum cymosum and Hypnea musciformis were evaluated for physiological responses.•The presence of mud and acidic conditions caused lethality and metabolic damages.•The acidified condition had the greatest impact over physiology of both species.•The toxicity effects of mining tailings are intensified by abiotic changes.