Which of the following is false concerning the development of dead zones in coastal waters, for example, the dead zone in the gulf of mexico?

a. higher levels of nutrients entering streams and ultimately the oceans lead to overproduction of algae and cyanobacteria.
b. when alive, the algae and cyanobacteria photosynthesize and produce oxygen but only during the daylight hours.
c. high concentrations of algae and cyanobacteria require oxygen to survive during the dark hours of the day, leading to depletion of oxygen levels.
d. when they die, algae and cyanobacteria sink to the bottom of the coastal zones where heterotrophic aerobic bacteria feed on them and deplete the water of oxygen.
e. dead zones in coastal waters of the oceans have been a common occurrence for many thousands of years.