Corals reefs face double threats from rising atmospheric carbon dioxide: severe heat stress and ocean acidification.
Corals reefs face double threats from rising atmospheric carbon dioxide: severe heat stress and ocean acidification. Severe heat stress causes bleaching (the expulsion of corals’ food-producing algae). Ocean acidification (the drop in seawater pH as the ocean absorbs carbon dioxide) reduces the availability of calcium minerals for skeleton building and repair. The combination of these two threats poses a Catch-22 for coral reefs. In many cases, the longer a reef is protected from severe heat stress, the more time the ocean has to absorb carbon dioxide, and the greater the threat the reef will face from acidification by that point in time.
The maps at right show how this relationship is likely to play out in the tropical Pacific, based on modeling research led by scientists at NOAA’s Atlantic Oceanographic and Meteorological Laboratory. The top map shows the year in which heat stress sufficient to cause severe bleaching (8 degree heating weeks) is likely to become a yearly event, causing severe degradation of the reefs and the goods and services they provide. The bottom map shows the projected declines, by that year, in how saturated seawater is with the mineral aragonite, the form of calcium carbonate used by growing corals.
Corals close to the equator—such as around the Solomons Islands—are projected to experience potentially fatal levels of heat stress on a yearly basis in less than 15 years with continued high rates of carbon dioxide emissions. Meanwhile, reefs at higher latitudes, such as those around Fiji or Hawaii, may have three decades before they hit that threshold. This latitude-linked pattern is consistent for reefs around the globe. (See global views of heat stress and aragonite saturation state maps.)
Continue reading at NOAA.
Image via Pixabay.
