Coral reefs that provide habitat for 25% of sea-dwelling fish species may be on the verge of another mass bleaching event, indicating that the coral are losing contact with the algae they depend on to survive. A U.S. researcher is pointing to warming oceans as the cause.
The relationship between the coral and the algae, zooxanthellae, “thrives within a pretty tight range of ocean temperatures, and when water warms above normal levels, coral tends to expel its algal lifeline,” Mother Jones reports. “In doing so, coral not only loses the brilliant colors zooxanthellae deliver—hence, ‘bleaching’—but also its main source of food. A bleached coral reef rapidly begins to decline.”
Coral bleaching began in the 1980s, and the first known global bleaching in Earth’s history took place in 1998, after an unusually strong El Niño raised ocean temperatures, explains C. Mark Eakin, coordinator of the Coral Reef Watch program at the U.S. National Oceanic and Atmospheric Administration (NOAA).
“Eakin is concerned about a relapse, because the oceans are relentlessly warming, driven by climate change from ever-increasing greenhouse gas emissions,” Philpott writes. “As heat builds in the ocean, he says, coral become more vulnerable to bleaching.”