c. consumption of waters' oxygen
Although algae produces oxygen during photosynthesis, in an algae bloom the algae is growing at a rapid rate which causes the algae to use more oxygen then it actually produces. When algae is growing rapidly it needs to use oxygen in order to break down glucose into energy through a process called cellular respiration. Cellular respiration requires large amounts of oxygen, so the faster the algae is growing the faster it uses oxygen draining it from the waters the algae lives in and thereby depleting the aquatic environment of oxygen.
