Microscopic organisms increase coral erosion in acidic waters

Editor's note: This web story is courtesy of Erica Rule of NOAA's Atlantic Oceanographic & Meteorological Laboratory. The story can be found at AOML's website.

Corals live and thrive by maintaining a careful balance between their growth and natural erosion. Scientists already know the projected increases in carbon dioxide absorbed into the global ocean from the atmosphere, known as ocean acidification, will slow the rate at which corals build the hard calcium carbonate skeletons that are the foundation of their habitat. A new NOAA-led study published online today in PLOS ONE demonstrates that in naturally highly acidified waters, coral skeletons face increased erosion or eating away of reef structure by microscopic organisms called microborers.

A team led by coral ecologist Ian Enochs at NOAA’s Atlantic Oceanographic & Meteorological Laboratory and the Cooperative Institute for Marine and Atmospheric Studies at the University of Miami confirmed the results during a study at the remote Pacific island of Maug, in the Northern Marianas Islands.

The region contains natural carbon dioxide seeps that bubble from the ocean floor, lowering the pH of the surrounding waters and providing a natural laboratory to study ocean acidification conditions predicted to occur by the end of the century.  By placing small blocks of calcium carbonate in acidified areas of lower pH, and in unaffected control sites for a period of three months, scientists were able to compare the amount of bioerosion that occurs with increasing ocean acidification.

Microscopic algae that naturally erode all calcium carbonate structures in the reef environment increased their erosion of coral in the most acidified waters. The microscopic algae left behind a network of microscopic cavities, smaller than the average diameter of human hair. This is the first research to demonstrate this relationship between increased ocean acidification and increased bioerosion by microscopic organisms outside the laboratory in a complex, real-world ecosystem.

The study was made possible by support from NOAA’s Coral Reef Conservation Program and NOAA’s Ocean Acidification Program. Read more about NOAA’s research into the effects of Ocean Acidification at Maug here. 

For more information contact Monica Allen, director of public affairs for NOAA Research at 301-734-1123 or by email at monica.allen@noaa.gov