Answer :
The answer is "d. increased temperature".
At the point when corals are stressed by changes in conditions, for example, temperature, light, or supplements, they remove the symbiotic algae living in their tissues, making them turn totally white. Hotter water temperatures can result in coral bleaching. At the point when water is too warm, corals will oust the algae living in their tissues, making the coral turn totally white. This is known as coral bleaching.
When a coral blanches, it isn't dead. Corals can endure a bleaching occasion, yet they are under more pressure and are liable to mortality.
Answer: d.increased temperature
Explanation:
The colony of coral polyp (coral reef) and algae lives in mutualistic association in oceanic waters. In this association the coral reef receives it's color and algae receives food and shelter. The increase in temperature is the abiotic factor responsible for the removal of the algal colony from the coral reef. The increase in temperature of oceanic water, causes the algal colony to swell and the algal colony get remove from the coral reef . The coral reef looks white due to the composition of calcium carbonate. This phenomena is called as coral bleaching.