Which of the following is true about oxygen concentration in anoxic environments?

In anoxic environments, the oxygen concentration is entirely absent or extremely low. Anoxia refers to a condition where oxygen levels fall below the threshold needed to sustain aerobic life, which is essential for most fish and other aquatic organisms. Without adequate oxygen, aerobic processes that many organisms rely on for survival cannot occur, leading to significant ecological consequences, including the decline or absence of aquatic life.

This condition can arise in various environments, such as deep water layers of lakes and oceans, sediments, or areas affected by excessive nutrient loading leading to hypoxia and subsequently anoxia. Therefore, the complete absence of oxygen characterizes an anoxic environment, making it inhospitable for aerobic organisms like most fish, which rely on dissolved oxygen for respiration.

Understanding anoxia is crucial in comprehending aquatic ecosystems and the factors that influence species composition and biodiversity in those environments.