For optimum no-decompression bottom times, plan repetitive dives so that each successive dive is to a _____ depth.

The choice of planning repetitive dives to a shallower depth is based on how the human body absorbs and expels nitrogen during dives. When divers descend, their bodies absorb nitrogen from the air they breathe. The deeper the dive, the more nitrogen is absorbed due to increased pressure.

If a diver decides to repeat dives, descending to a shallower depth allows the body to off-gas this nitrogen more effectively, reducing the risk of decompression sickness, commonly known as "the bends." By gradually decreasing depth, divers can optimize their no-decompression limits, making each subsequent dive safer. This practice aligns with safe diving protocols, which emphasize the importance of managing nitrogen levels in the body to prevent complications related to decompression.

In contrast, diving deeper or to the same depth could lead to increased nitrogen absorption, heightening the risk of decompression illness, particularly in repetitive dive situations. Variable depths may complicate the nitrogen absorption and off-gassing process, making it harder to plan and execute dives safely. Hence, planning each successive dive to be shallower is the optimal approach for safety and compliance with no-decompression guidelines.