Oxygen Levels in the Photic Zone Fluctuate Over the Course

Multiple Choice

Oxygen levels in the photic zone fluctuate over the course of a 24-hr period.If you were measuring dissolved oxygen over the course of the day,when would you expect to see the lowest levels of oxygen and why?

A) Mid-morning -- because fish are most active and their respiration rates are highest.
B) Early afternoon -- when the surface water warms up and sinks to the bottom.
C) Mid-afternoon -- because the activity of the Calvin cycle (the dark reactions) of photosynthesis are at their peak.
D) Early evening -- when animals come to feed and disturb the surface waters.
E) During the night -- because the light reactions of photosynthesis are inactive.