Scientists trying to size up the toll climate change will take on Florida reefs may have found their answer at the bottom of the ocean on the other side of the world.
In a study published this week in the journal Nature Climate Change, a team looked at an ancient, buried volcano near the Mariana Islands in the Pacific Ocean where carbon dioxide bubbling from the sea floor mirrors projections for future levels of ocean acidification. The results? A real world yardstick showing the point at which healthy reefs collapse and algae takes over, leaving a bleak rocky moonscape.
“It’s a grim picture,” said lead author Ian Enochs, an assistant scientist at the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies. “It viscerally hits home more than the numbers.”
Lab experiments have long led scientists to conclude that as the ocean becomes more acidic, coral and other sea life will suffer. Already, increasing acidification in Florida waters have caused some Keys reefs to stop growing, Enochs said.
Scientists worry because coral reefs provide a natural barrier against sea rise and more powerful hurricanes — two other byproducts of climate change. But while lab experiments have allowed them to examine changes species by species, they could only theorize about possibilities for complex reefs, an ecosystem filled with fish, anemones, sponges and a web of marine life working in tandem. So more and more they are turning to ocean vents to gain a better understanding of how carbon plays into the delicate balance.
“In reality the ecosystems are complex,” said Enochs. “And scaling up from the experiments is difficult.”
About two years ago, while Enochs was in the Mariana Islands, a U.S. territory where government scientists are closely monitoring reefs, he heard about the bubbling sea floor near the Maug Islands. The bubbles are caused by carbon dioxide escaping vents near buried volcanoes. When the gas dissolves in the ocean, it drives up acidity, which can stunt growth or kill sea life. Such vents — also found in Italy, Japan and Papua, New Guinea — have increasingly drawn the interest of climate scientists trying to pin down how acidity could change the world’s oceans.
Enochs thought the vents would provide a perfect chance to measure the “slippery slope to slime,” when coral begin to give way to algae. The Maug Islands had also never been studied before, he said. A two-day boat ride from an already remote chain of volcanic islands on the edge of the deepest trench in the world, they are like the glaciers of the sea and remote even for oceanographers.
“Therein lies the adventure,” he said. “You have this amazing natural laboratory where you can look at what predictions for the end of the century look like today.”
The three-island chain, which has been uninhabited since the late 17th century, makes up the outer rim of a submerged volcano. In the middle, a caldera — a kind of lake in the middle of the Pacific — stretches for more than a mile. The shallow waters near the islands are filled with pristine reefs. All around the bubbling sea floor “is like diving through champagne,” Enochs said.
Because they are so remote, none of the human-generated stresses that can sicken reefs — or influence the study’s findings — exist.
“You’re looking at a place that literally a handful of people can get to every year,” Enochs said. “ So you’re not dealing with areas where people are taking tons of fish, areas where there’s runoff and coastal pollution. You’re not dealing with a hugely impacted ecosystem.”
The team picked three sites to study. One spot reflected carbon dioxide at levels now generally occurring in the ocean, a second had medium levels and the third lay nearest the vents where carbon equals projections for the next century. For three months, the team logged acidity, temperature and light, tracking both ocean conditions and the sea life living there. They also captured images using new equipment UM helped develop that allowed them to photograph huge swaths of sea floor — up to nearly 11 yards at a time. The UM center works closely with scientists at the National Oceanic and Atmospheric Administration’s research lab on Virginia Key.
Closest to the vents, the team found hardly any coral and the sea floor matted with algae. For the first time, researchers were able to document a complete shift from coral to algae. While a recent study found some coral might acclimate to increased levels of acidity, Enochs said near vents in Maug, where acidity occurs in amounts projected for the next century, coral did not adjust.
“It absolutely gives us a measuring stick,” Enochs said.
That measuring stick could help researchers better understand how much acidity reefs can tolerate and what events might hurt or help them. For example, scientists know that hurricanes can stress reefs. After Hurricane Isaac passed by Florida in 2012, Enochs said researchers recorded higher ocean acidity as sea life struggling to breathe released more carbon — like a winded runner — in the churned-up water. Likewise, some elements of the ocean can help counter rising carbon dioxide. Three years ago UM researchers found South Florida seagrass beds, like forests, absorb carbon to help protect reefs.
For now, trying to place Florida reefs on the Maug measuring stick is complicated because the pollution and and over-fishing that damage Florida reefs don’t stress the remote Pacific island tract. The team is planning more research, he said, but pointed out that if a reef as pristine as Maug’s collapses at predicted levels of acidification, South Florida’s already stressed reefs will almost surely suffer.
“If a reef so far removed is still seeing collapses,” Enochs said, “it casts a scary shadow on what might occur on Florida reefs.”