RAS question
Coral bleaching occurs primarily due to:
Correct answer: (C) Rise in sea surface temperature.
Coral bleaching occurs primarily due to a rise in sea surface temperature, which stresses corals and makes them expel their symbiotic algae.
Explanation
Coral bleaching is the whitening of corals after stress breaks the relationship between the coral animal and its symbiotic algae, zooxanthellae. Elevated sea surface temperature is the primary stress, and NOAA National Ocean Service describes this mechanism: when water becomes too warm, corals expel the algae living in their tissues, leaving the coral completely white. This does not mean the coral is immediately dead, but the coral is under greater stress and may die if the algae loss and stress continue. NOAA National Ocean Service also states that increased ocean temperature caused by climate change is the leading cause of coral bleaching, which is why a rise in sea surface temperature is the best answer.
Why the other options are wrong
- (A) A decrease in salinity can stress corals, and NOAA notes that storm precipitation can dilute ocean water, but it is not the primary cause identified here.
- (B) Tectonic activity is not linked to the main bleaching mechanism of heat stress and algae expulsion.
- (D) Increased rainfall may contribute indirectly by diluting near-shore waters, but NOAA identifies increased ocean temperature as the leading cause of coral bleaching.
Concept
This tests coral reef ecology, especially the stress response of coral-algae symbiosis under climate change. It recurs in RAS Environment and Ecology because coral reefs are a standard indicator topic for ocean warming and ecosystem vulnerability.