DeCarlo, T.

Hidden battles on reefs - How will corals fare in a changing ocean?

2015

Woods Hole Oceanographic Institution (WHOI)

"How do you drown a coral reef? The very idea seems unfathomable for animals that spend their entire lives under water. But the deep ocean is actually riddled with 'drowned' coral reefs - the remains of ancient reefs that slipped into the dark ocean depths and starved without sunlight. Coral reefs need to get it just rightsubmerged in the sea, but shallow enough for the corals symbiotic photosynthetic algae to soak up sunlight. Too deep and the ecosystem wastes away without solar energy to make food. Too shallow and corals dry out at low tide. This delicate balance is achieved by a constant tug-of-war, which most people overlook. Day in and day out, as corals build their skeletons up toward the sea surface, other organisms are eroding and dissolving the skeletons to build their own homes, cutting down the corals hard work.his delicate balance between calcium carbonate production and removal is threatened by ocean acidification, the decline in seawaters pH driven by rising carbon dioxide (CO2) levels in the atmosphere. Changing ocean conditions are bound to affect the bioeroders, too. Will lower-pH seawater hinder them, or will it help them and tip the balance even further against corals? Members of Woods Hole Oceanographic Institution (WHOI) have been investigating the impacts of ocean acidification on coral reefs. The team has searched the ocean for reefs that are able to tolerate living in seawater that naturally has a pH lower than the seawater typically found in the tropics. This search took us from the Pacific coast of Panama, across a vast stretch of the equatorial Pacific Ocean, and into the South China Sea - just shy of half the circumference of the globe. On their search across the Pacific, they identified a number of reefs that are naturally happen to be bathed in seawater with pH levels today that are as high as those expected for much of the tropical ocean by the end of this century. Examining the 3-D CAT scans of coral skeletons collected from these reefs, they found that relatively acidic (lower-pH) reefs were more heavily bioeroded than their higher-pH counterparts. So how do you drown a reef? The answer is 'add acid,' and to do it much faster, add nutrients. Both are happening now on many of our coral reefs. The encouraging news in their findings is that people can take action to protect their local reefs. Most excess nutrients added to the ocean come from human activities that cause runoff from sewers, septic tanks, roads, and fertilizers. If people can limit these sources of nutrients to the coastal ocean, the bioeroders will not have such an upper hand, and the balance will tip much more slowly toward erosion and dissolution of coral reefs."

This research is funded by the National Science Foundation (NSF), the Nature Conservancy, and the National Oceanic and Atmospheric Administrations Coral Reef Conservation Program

National Science Foundation

the Nature Conservancy

Coral Reef Conservation Program