Coral Reefs and Climate Stress

Passage

Coral reefs, often described as the rainforests of the ocean owing to the extraordinary biodiversity they support relative to their spatial extent, are facing an unprecedented ecological crisis driven primarily by the twin stressors of rising ocean temperatures and ocean acidification, both of which are direct consequences of increasing atmospheric concentrations of carbon dioxide produced by human industrial activity. Corals are colonial organisms that depend on a symbiotic relationship with microscopic algae known as zooxanthellae, which live within coral tissues and provide up to ninety percent of the coral's energy requirements through photosynthesis, while simultaneously producing the vivid colours characteristic of healthy reef ecosystems. When ocean temperatures rise even one or two degrees Celsius above seasonal norms for extended periods, corals expel their zooxanthellae in a stress response known as bleaching, which leaves the coral white, energetically depleted, and highly vulnerable to disease and mortality. Global surveys conducted by marine scientists indicate that over fifty percent of the world's coral cover has been lost since the 1950s, with mass bleaching events occurring with increasing frequency and severity, most dramatically affecting the Great Barrier Reef off the coast of Australia. The ecological consequences extend far beyond the reefs themselves, as an estimated five hundred million people worldwide depend on reef ecosystems for food security, coastal protection, tourism income, and the rich biological diversity from which numerous pharmaceutical compounds have been derived.