Which component is critical for supporting life in aquatic environments?

Oxygen levels are critical for supporting life in aquatic environments because they are essential for the respiration of most aquatic organisms, including fish, invertebrates, and aerobic bacteria. Oxygen dissolved in water is what enables these organisms to carry out cellular respiration, allowing them to convert food into energy.

In many aquatic ecosystems, the concentration of dissolved oxygen can fluctuate based on various factors, including water temperature, salinity, and the presence of plants and algae that produce oxygen during photosynthesis. When oxygen levels drop significantly, it can lead to hypoxia, a condition that can be detrimental or even fatal to marine life.

In contrast, while pollution levels can adversely affect aquatic environments, they do not inherently support life. Sunlight penetration is vital for photosynthetic organisms, but it does not directly support the respiration needs of most aquatic life. Water depth can influence temperature and pressure conditions but is not directly linked to the vital life-supporting processes as oxygen levels are.