Below , in the brine , the number of cells is much lower than in the halocline . Extremophiles are most common , including some of the deep-sea hydrothermal vent archaea and bacteria . In the brine , the abundance of cells is much lower ; extremophiles predominate , including members of the deep-sea hydrothermal vent euryarchaeota ( DHVEs ) , Methanohalophilus and Proteobacteria .