Washington: A new study has revealed that lowering of the ocean's pH is making it harder for corals to grow their skeletons and easier for bioeroding organisms to tear them down.
According to the study, these reefs may have a harder time growing toward the ocean surface, where they get sunlight they need to survive.
The study, led by scientists at Woods Hole Oceanographic Institution (WHOI), highlights the multiple threats to coral reef ecosystems, which provide critical buffers to shoreline erosion, sustain fisheries that feed hundreds of millions of people, and harbor 25 percent of all marine species.
The researchers point to a key management strategy that could slow reef decline: reducing the input of nutrient pollution to the coastal ocean from human activity such as runoff from sewers, septic tanks, roads, and fertilizers.
Corals make their skeletons out of calcium and carbonate ions from seawater, constructing massive colonies as large as cars and small houses. As the ocean absorbs excess carbon dioxide from fossil-fuel burning, it spurs chemical reactions that lower the pH of seawater, a process known as ocean acidification. The process removes carbonate ions, making them less available for corals to build skeletons.
The new study shows that additional nutrients provide a dramatic boost for bioeroders that, combined with lower pH conditions, will tip this balance in favor of erosion. The bioeroders are filter feeders, sifting particles of food out of seawater.
Nutrients spur the growth of plankton, supplying food for large populations of bioeroders that burrow into coral skeletons.
The researchers found that relatively acidic (lower-pH) reefs were more heavily bio-eroded than their higher-pH counterparts. But their most striking finding was that in waters with a combination of high nutrient levels and lower-pH, bio-erosion is ten times higher than in lower-pH waters without high nutrient levels.
The study was published in the journal Geology.