Complex sentence: If sufficient sulfate is present to support sulfate reduction, the sulfide, produced in the sediments, diffuses upward into the anoxic bottom waters, where purple sulfur bacteria can form dense cell masses, called blooms, usually in association with green phototrophic bacteria.
Split into simpler sentences: If sufficient sulfate is present to support sulfate reduction, the sulfide produced in the sediments will diffuse upward into the anoxic bottom waters. This allows purple sulfur bacteria to form dense cell masses (blooms), usually in association with green phototrophic bacteria.