These include juveniles of various species with difficulty constructing skeletons, fewer varieties of corals, less coral cover, more algae growth and more porous corals with greater signs of erosion from other organisms.
The new research results, published in a paper in Geophysical Research Letters, a journal of the American Geophysical Union, explain the biological and geomorphological causes of the more acidic waters near Palau's Rock Islands.
The paper also describes a surprising second finding--that the corals living in those more acidic waters were unexpectedly diverse and healthy.
The unusual finding, contrary to what has been observed in other naturally low pH coral reef ecosystems, has important implications for the conservation of corals in all parts of the world.
"When you move from a high pH reef to a low pH neighboring reef, there are big changes, and they are negative changes," said Cohen, a co-author of the paper and principal investigaor of the project.
"However, in Palau wherever the water is most acidic, we see the opposite. There's a coral community that is more diverse, hosts more species and has greater coral cover than in the non-acidic sites.
"Palau is the exception to other places scientists have studied."
Through analysis of the water chemistry in Palau, the scientists found that the acidification is primarily caused by the shell-building done by organisms living in the water, called calcification, which removes carbonate ions from seawater.
A second reason is the organisms' respiration, which adds carbon dioxide to the water when they breathe.
"These things are all happening at every reef," said Cohen. "What's critical is the residence time of the seawater."
|Contact: Cheryl Dybas|
National Science Foundation