Coral Reefs and Ocean Acidification

Passage

Coral reefs, which occupy less than one percent of the ocean floor yet support approximately twenty-five percent of all known marine species, are facing an existential threat from the twin consequences of anthropogenic climate change: rising sea temperatures and ocean acidification. When atmospheric carbon dioxide dissolves into seawater, it forms carbonic acid, progressively lowering the pH of the ocean and reducing the availability of carbonate ions that corals and other calcifying organisms require to construct their calcium carbonate skeletons. As ocean acidity increases, coral structures become weaker and more susceptible to erosion, while recruitment of juvenile corals onto damaged reefs declines markedly. Compounding this chemical threat, elevated water temperatures trigger coral bleaching events, during which the symbiotic algae known as zooxanthellae are expelled from coral tissues, depriving the coral of its primary energy source and leaving it vulnerable to disease and mortality. Mass bleaching events that were once considered rare occurrences now strike major reef systems such as the Great Barrier Reef with alarming frequency, and projections suggest that most tropical reefs could experience annual bleaching conditions before mid-century if greenhouse gas emissions continue along current trajectories. The ecological and economic ramifications are profound, as hundreds of millions of people depend on reef ecosystems for food security, coastal protection from storm surges, and tourism revenue, making coral conservation an urgent priority for both environmental science and international climate policy.