What is a direct cause of coral bleaching? a. exposure to sunlight b. the loss of symbiotic algae c. overgrazing by fish d. all of the above

Option B, the loss of symbiotic algae

Explanation:

Coral and algae form a symbiotic relationship in which the chlorophyll (the photosynthesis pigment) is responsible for the providing food and color to the coral. Due to unavoidable environmental conditions such as rising temperature of sea water, change in chemical constituents of sea water etc, the rate of photosynthesis done by algae  reduces due to the loss of chlorophyll and thus the coral turns white is color. The change of color of coral into white is called as coral bleaching

Thus option B, is correct.

b. the loss of symbiotic algae

Explanation:

Coral bleaching occurs when some stress, usually thermal, causes the coral to expel the microscopic algae that live in symbiosis with it. These algae, called zooxanthellae, are the coral's main source of food and give it color. When the sea gets too hot, they leave. The coral starves and is more susceptible to disease. In many cases it even dies.

b.