Friday, May 16, 2014

Coral Reefs Protect Shorelines By Reducing Wave Energy By 97 Percent, Study Finds

Coral reefs provide substantial protection against wave energy, lessening the impact of sea level rise and intense storm surges for 7 million people in the U.S. alone, according to a new report.

The report, published this week in the journal Nature Communications, reviewed 255 studies on the protective nature of coral reefs and found that reefs reduce wave energy by 97 percent on average, causing the waves that reach the shoreline to be significantly calmer than they would have been without the reefs. Michael Beck, one of the authors of the report and senior scientist for the Nature Conservancy, said he was surprised at the 97 percent average for reef wave reduction. He said he knew it would be a large number — other studies have shown that reefs are effective at reducing wave energy, but none yet had quantified it ocean-wide — but he didn’t know just how big.

The report also found that worldwide, 197 million people are protected by reefs, and that maintaining the health of coral reefs is far less expensive than installing artificial defenses — according to the report, the median cost of building artificial wave defenses is $19,791 per meter, while the median cost of coral restoration projects is $1,290 per meter. Beck said the Nature Conservancy is working in a coral reef in Grenville, Grenada to build back the reef’s crest, the highest part of the reef that’s the most important for wave-breaking. He said degredation of the reef crest, which has been caused over the last 50 years by climate change, pollution, and sand mining, can explain a “huge amount” of the erosion and sedimentation that’s been occurring in the bay.

“A variety of causes has led to a little bit of degradation in height in the reef, and when you’ve lost that height in the reef, you can suddenly explain a huge amount of problems that have been happening,” he said.

Beck’s team has been been building back the reef in Grenada by using old coral rubble and concrete blocks, then trying to regrow the living coral on those structures. Projects like that, he said, are important to coral reefs’ survival — though coral is threatened gravely by climate change and ocean acidification, he said reefs “can be resilient” and recover from stresses like bleaching. He pointed to a mass bleaching event that occurred in 1998, after El NiƱo drove up water temperatures worldwide, as evidence. Though many were worried the reefs wouldn’t bounce back from this event, which was the most extensive and severe in history, certain reefs did recover, despite significant losses worldwide.

“Those reefs that were managed well, where you reduce the other stressors like pollution and overfishing, recovered,” he said. “Living coral came back and came back in quite good abundances in places were coral reefs were managed well.”

That event points to the need for better reef management, Beck said, especially now, as reefs around the world continue to suffer the effects of warming oceans, pollution, fishing practices and other impacts. Elkhorn coral, which play an integral role in the reef ecosystem of the Florida Keys, are being killed off by White Pox disease, which one researcher says is likely caused by untreated human sewage that enters the ocean through leaky septic systems in Florida. And outside of the 1998 event, scientists have found other significant evidence of coral bleaching, an effect that’s due to warmer-than-usual ocean temperatures and is likely to get worse as the ocean warms.

Other coastal and marine ecosystems provide protection from storm surge, sea level rise and erosion, but they too are struggling with human-induced impacts — in fact, Beck said coral reefs are in better shape worldwide than oyster reefs and mangrove forests. These coastal ecosystems have also been found to be a cost-effective way of providing protection — an April report noted restoring ecosystems like oyster reefs can create more jobs than offshore oil development and provide $15 in net economic benefits for every $1 invested. More