Man, now is just not a good time to be a coral reef. I mean, it’s never really easy. We think of corals as being rock-like, but they’re actually anything but. A Nov. 28 news release from the University of Hawaii breaks down coral’s precarious existence rather elegantly:
“Coral reefs persist in a balance between reef construction and reef breakdown. As corals grow, they construct the complex calcium carbonate framework that provides habitat for fish and other reef organisms. Simultaneously, bioeroders, such as parrotfish and boring marine worms, break down the reef structure into rubble and the sand that nourishes our beaches. For reefs to persist, rates of reef construction must exceed reef breakdown.”
Any change in that balance threatens their existence. Back in November 2013, researchers from the National Oceanic and Atmospheric Administration (NOAA) and the University of Hawaii announced that their data showed that the very traits that make corals so abundant may also put them at a disadvantage when having to deal with changes in ocean chemistry caused by climate change.
As levels of carbon dioxide rise in our atmosphere, the ocean’s acidity (pH) increases. Until recently, researchers just thought that increased acidity spelled doom for species like coral. But now, according to that Nov. 28 UH news release, even a lowering of our ocean’s pH level can be catastrophic for coral:
Researchers with the university’s Hawaii Institute of Marine Biology (HIMB) began by using small blocks of dead coral skeleton (called “bioerosion blocks”). Their experiment involved placing these blocks on coral reefs for a year:
“The researchers placed the bioerosion blocks along a 100-foot transect on shallow coral reef in Kāne‘ohe Bay, taking advantage of natural variability of pH in coastal reefs. The study compared the influence of pH, resource availability, temperature, distance from shore, and depth on accretion-erosion balance. Among all measured variables, pH was the strongest predictor of accretion-erosion. Reefs shifted towards higher rates of erosion in more acidic water – a condition that will become increasingly common over the next century of climate change.”
Using high-resolution CT scans, the researchers were able to study accretion and erosion in the blocks in minute detail. Their findings don’t bode well for the species.
“It was surprising to discover that small-scale changes in the environment can influence ecosystem-level reef processes,” said Nyssa Silbiger, the lead study author and a doctoral candidate at the HIMB. “We saw changes in pH on the order of meters and those small pH changes drove the patterns in reef accretion-erosion.”
Photo of coral in Hawaii: Brocken Inaglory/Wikimedia Commons