Final answer:
Coral bleaching occurs when rising ocean temperatures cause coral reefs to expel their symbiotic algae, resulting in loss of color. Increased levels of carbon dioxide further threaten corals by affecting their calcification process. This decline in coral reefs poses a threat to biodiversity and coastal economies.
Step-by-step explanation:
Coral bleaching refers to the phenomenon where coral reefs expel their symbiotic algae, resulting in the loss of their characteristic color. This expulsion is triggered by rising ocean temperatures, caused by global warming due to fossil fuel emissions. The excessive warmth causes the coral organisms to expel their food-producing protists, known as zooxanthellae, leading to bleaching. When the protists leave, the corals lose their color and turn white.
Rising levels of atmospheric carbon dioxide further threaten the corals by lowering the pH and increasing ocean acidity. This interferes with the calcification process that corals use to build their calcium carbonate homes. The decline of coral reefs not only affects biodiversity and the ecosystem, but also poses a serious threat to coastal economies since coral reefs are important tourist destinations.