What occurs during coral bleaching? Explain why bleaching may be an adaptation that is helpful to corals but why extended bleaching may kill coral polyps.

Coral bleaching is a phenomenon in which corals lose their color and turn white due to the expulsion of microscopic algae called zooxanthellae, which live inside the coral polyps and provide them with essential nutrients and energy through photosynthesis. The loss of these algae results in the coral losing its color, thus appearing "bleached."

Zooxanthellae are essential to the health and survival of corals. They provide corals with about 90% of their energy needs through photosynthesis, which also helps in the formation of coral reefs. The symbiotic relationship between corals and their zooxanthellae benefits both the organisms, allowing the corals to grow and maintain healthy reef ecosystems.

Coral bleaching occurs when environmental factors, such as high water temperatures, pollution, and increased exposure to ultraviolet (UV) light, put stress on the corals. In response to these stresses, corals may expel their zooxanthellae to protect themselves, which may be a helpful short-term adaptation against the harsh conditions.

In the short term, coral bleaching can be helpful for corals, as it allows them to rid themselves of damaged or less efficient zooxanthellae. Once environmental conditions improve, healthy zooxanthellae can repopulate the coral polyps, restoring the corals' energy production and color.

However, if the stressful conditions persist, corals may continue to lose their zooxanthellae without sufficient recovery, leading to extended bleaching. Extended bleaching can be detrimental to coral polyps, as they rely heavily on zooxanthellae for energy and nutrients. Without these algae, corals struggle to produce the energy they need to sustain basic functions, such as growth, reproduction, and maintaining their structural integrity. As a result, they become more susceptible to diseases, and in severe cases, extended bleaching can lead to the death of coral polyps. In conclusion, coral bleaching is an adaptation that allows corals to recover from short-term environmental stressors. However, extended bleaching can have severe long-term consequences for corals, leading to their decline and death.