Which factor contributes to coral bleaching?

Elevated sea temperatures are a primary contributor to coral bleaching. Corals have a symbiotic relationship with zooxanthellae, which are microscopic algae living in their tissues. These algae provide essential nutrients to corals through photosynthesis and give them their vibrant colors. However, when sea temperatures rise beyond the normal range—often due to climate change—coral polyps become stressed. This stress can lead to the expulsion of the zooxanthellae from their tissues, resulting in a loss of color and the bleaching effect.

Once bleached, corals are more vulnerable to disease and have reduced chances of survival because they lack the energy and nutrients usually supplied by their symbiotic partners. Prolonged periods of elevated temperature can lead to widespread coral mortality, impacting reef ecosystems significantly.

Though low salinity, increased sunlight availability, and high nutrient levels can affect coral health in various ways, they are not as directly linked to the immediate phenomenon of bleaching as elevated sea temperatures. The primary threat to coral reefs from these other factors usually operates in different contexts, such as creating poor water quality or altering the reef's ecological balance.