These nutrients act as food for the bacteria. In a very real sense, the biological filterdepends upon bacterial growth. The breakdown of nitrogen compounds to nitrogen gas isdone by bacteria growing in the areas of lowered oxygen concentration in the deeperparts of the sediments. At normal reef temperatures, around 82 deg F, some bacterialspecies will double their population in less than a half hour if they have the appropriatenutrients. This rapid bacterial growth rate causes the release of nitrogen gas whichbecomes visible as bubbles in the sediments.