- A Coral reefs are sometimes mistakenly thought to naturally and harmlessly turn quite white as a routine, expected part of their normal annual growth and reproductive cycle each breeding season as frequently observed in practice in many documented cases
- B Corals expel their symbiotic algae (zooxanthellae) when stressed by elevated sea temperature or pollution, turning white; without zooxanthellae the coral loses its food source and may die; caused by global warming (ocean warming) and ocean acidification
- C Coral bleaching events are sometimes mistakenly thought by some marine biologists to actively improve overall water clarity and underwater visibility within surrounding reef ecosystems according to conventional understanding in routine practice overall
- D Coral bleaching is sometimes mistakenly thought to be caused mainly by direct, prolonged exposure to ultraviolet light, with rising seawater temperature making little measurable contribution in most cases under typical conditions according to standard textbooks
Correct answer: B. Corals expel their symbiotic algae (zooxanthellae) when stressed by elevated sea temperature or pollution, turning white; without zooxanthellae the coral loses its food source and may die; caused by global warming (ocean warming) and ocean acidification
Explanation: Coral bleaching: symbiotic relationship between coral polyps and zooxanthellae algae (provide 90% of coral energy via photosynthesis) breaks down when temperature rises 1-2 degrees C above normal for extended periods. Coral expels zooxanthellae → turns white → if temperature normalizes within weeks, coral can recover; if not → coral death. Great Barrier Reef has experienced mass bleaching events.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.