Final answer:
Coral bleaching is primarily caused by increased water temperatures leading to the expulsion of vital, symbiotic algae from coral reefs, amplified by rising ocean acidity due to higher CO₂ levels.
Step-by-step explanation:
B) Increased water temperature is the primary factor that can lead to coral bleaching.
Coral bleaching is a phenomenon that occurs when coral reefs undergo stress due to increased water temperature. This warm temperature causes the coral to expel the symbiotic algae (zooxanthellae), which are crucial for coral health and color. The absence of these algae leads to the whitening or 'bleaching' of corals, significantly impacting their ability to survive, since the algae provide them with the majority of their energy through photosynthesis.
Additionally, rising CO₂ levels result in increased ocean acidity, further affecting corals by hindering their calcification process, crucial for building their calcium carbonate skeletons. This combination of high temperatures and ocean acidification can lead to a decline in reef biodiversity and productivity, as species that depend on reefs for food and shelter are also affected.