According to endosymbiosis theory, host archaea engulfed which then allowed both popopulations to survive together.

According to endosymbiosis theory, host archaea engulfed aerobic bacteria, which then allowed both populations to survive together. Aerobic Bacteria grow in the presence of oxygen to oxidize glucose where water is produced. They are the largest and most common cause of clinical infections, such as tuberculosis. In contrast, anaerobic bacteria/organisms do not require oxygen for growth and may, in fact, die as a result of too much oxygen. 

The zone your looking for is the intertidal zone.