What is coral bleaching?

Coral bleaching refers specifically to the loss of symbiotic zooxanthellae, which are tiny algae that live within the coral's tissues. These algae provide essential nutrients to the coral through photosynthesis and also give corals their vibrant colors. When environmental stresses such as increased water temperatures, pollution, or changes in salinity occur, corals may expel these algae, leading to a paler or "bleached" appearance. This process signifies that the coral is in distress and can lead to coral death if the conditions do not improve and the zooxanthellae do not return.

In contrast, the other options describe phenomena that either do not pertain to the bleaching process or misinterpret the biological interactions involved in coral health. Coral bleaching is a critical concern in marine ecology as it serves as an indicator of reef health and the potential impact of climate change on marine ecosystems.