What restricts the amount of time diving animals can spend underwater?

Diving animals are restricted in their underwater time primarily by the need for oxygen, as they rely on aerobic respiration for energy. The duration they can stay submerged is influenced by factors such as their metabolic rate, the efficiency of their oxygen storage, and the ability to tolerate carbon dioxide buildup. Additionally, environmental factors like water temperature and depth can affect their physiological responses and limits on dive times.