Question

Choose the correct statements about corals?
A. Corals are invertebrate animals a few millimeter in diameter.
B. Corals are sensitive to heat stress and ocean pH change.
C. Corals provide algae with stable environment, CO\(_2\) and nutrients.
D. Corals bleach to get rid themselves of pathogens.

• A. C and D only
• B. A, B and C only
• C. A and B only
• D. A, B, C and D only

Hint:

Coral bleaching is a sign of severe stress, not a healthy cleaning process. It's the breakdown of the vital symbiosis between the coral animal and the algae that gives it color and most of its food.

Answer 1

The Correct Option is B

Step 1: Analyze statement A.
A coral reef is made of vast colonies of tiny animals called coral polyps. A single polyp is an invertebrate animal, typically only a few millimeters in diameter. Statement A is correct.

Step 2: Analyze statement B.
Corals have a narrow range of environmental tolerances. Increased ocean temperature (heat stress) and decreased pH (ocean acidification) are major stressors that can disrupt their symbiotic relationship with algae and lead to coral bleaching. Statement B is correct.

Step 3: Analyze statement C.
Corals live in a symbiotic relationship with microscopic algae called zooxanthellae. The coral polyp provides the algae with a protected environment and the compounds they need for photosynthesis (CO\(_2\) and nutrients like nitrates and phosphates). Statement C is correct.

Step 4: Analyze statement D.
Coral bleaching is the process where corals expel the symbiotic algae living in their tissues, causing them to turn completely white. This is a stress response, primarily to heat, not a mechanism to get rid of pathogens. The loss of the algae can lead to the coral's death. Statement D is incorrect. Conclusion: Statements A, B, and C are correct.