Since these chemicals are potentially toxic, wetland plants have developed means of removing these toxins. Other plants shift metabolism to produce malic acid, which unlike ethanol or acetaldehyde is not toxic. Most plants in wetlands are type C 4 because the photosynthesis that takes place in these plants uses oxygen, carbon dioxide, and water more efficiently than type C 3 under stressful conditions. Structurally, plants developed pores in their stems, leaves and roots so that oxygen rich air can reach the roots. Trees develop root systems that extend above the anaerobic level to find oxygen.
Animals also adapt to anoxic conditions.
They can do this by changing their biochemistry, their physiology, or their behavior. The biochemical changes in animals are much more limited than they were in either the bacteria or the plants because evolution has tended to favor aerobic respiration. Some animals, such as crabs, have been able to increase the efficiency of their respiratory system to remove oxygen from the environment. Others have developed behaviors that allow them to avoid the harshest stress from the environment. Human activities have greatly changed wetlands worldwide.