Explain why coral bleaching occurs in the absence of zooxanthellae and what alternatives can support coral survival?

• A. Without zooxanthellae, corals rely on heterotrophy but productivity and calcification drop; some corals can survive longer by capturing plankton, yet long-term survival is unlikely; recovery requires recolonization with symbionts.
• B. Bleaching occurs because corals cannot photosynthesize; alternatives include heterotrophy; but long-term survival is guaranteed.
• C. Bleaching happens due to pollution; alternatives include increasing nutrient input.
• D. Corals without zooxanthellae cannot survive at all.

Answer: (A)