Living organisms need oxygen in order to respire, which involves converting stored chemical energy into useful forms such as heat and kinetic energy. They require this energy in order to move, grow, reproduce and carry out all their daily activities. Plants produce oxygen via the process of photosynthesis, but animals have to take it in from the air or water in which they live.  Oxygen is not very soluble in water and it diffuses slowly through this medium. This means that aquatic ecosystems are particularly vulnerable to...