Living Diatoms Contain Brownish Plastids

Living diatoms contain brownish plastids. If global warming causes blooms of diatoms in the surface waters of Earth's oceans, how might this be harmful to the animals that build coral reefs?

A) The coral animals, which capture planktonic organisms, may be outcompeted by the diatoms.
B) The coral animals' endosymbiotic dinoflagellates may get "shaded out" by the diatoms.
C) The coral animals may die from overeating the plentiful diatoms with their cases of silica.
D) The diatoms' photosynthetic output may over-oxygenate the water.