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The Aua Transect

Saving the reefs one step at a time

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Coral Reef

Regional scientists conducted a survey in late May celebrating the 100th anniversary of the world’s oldest continuously monitored coral reef transect, located in American Sāmoa.

The Aua Transect of Tutuila island is a permanent line placed on the reef that scientists can observe over time. Because it provides a stable basis of comparison, differences in the reef are only seen in time, not in place, so measurements of change are more accurate. Surveyors use the transect to learn how to help the reefs survive the global stresses that are threatening coral throughout the Pacific.

“We need to learn to handle the reefs as best we can. [Observations show] how serious the effects on the reefs can be. The coral won’t necessarily ‘just grow back,’” Charles Birkeland, an emeritus professor in the Department of Biology at the UH at Mānoa, said in a phone interview.

One of the biggest lessons of the transect is that new coral growth needs a large substratum or a “big heavy block of dead coral” to develop safely, according to Birkeland.

Practices such as dynamite fishing and dredging do not only kill the fish and coral that are already present, they slow or prevent further growth by breaking up existing reefs.

Live coral gets crushed or smothered when it attaches to the constantly shifting rubble that is created when reefs are destroyed. Until a new substratum is formed — which can take decades or longer — it is difficult for new coral to survive. The reef is still recovering from destruction that occurred more than 50 years ago.

“We have to take care of the local, not just the global,” Birkeland said.

Terry P. Hughes, of James Cook University in Australia and his coauthors found in a March 16 report that “bolstering resilience will become more challenging and less effective in coming decades … Securing a future for coral reefs … ultimately requires urgent and rapid action to reduce global warming.”  

“That is the purpose of the transect – What can we do about it?” Birkeland said. “The bottom line is that we can learn about local effects and solutions. Even though the CO2 and global warming and ocean acidification are big problems, we have to maintain [the reefs] in the meantime.” 

Local attention to and knowledge of the reefs will help keep coral healthy in the short term so it can survive high levels of global stresses.

To that end, the University of Hawai‘i Sea Grant reached out to connect local students and the public, with the work that is happening at the transect. The reef needs a lot more care. Environmental agencies need people to measure the health of the water and fisheries need to know how fish live. The transect has brought attention to these needs, and the Samoans have risen to the challenge of bringing the reef back to health, according to Birkeland, who has shown that local efforts really can make a difference.

“If you look at early pictures of the reefs, they were very beautiful, but then canneries were put up in the ’50s,” Birkeland said.

In 1992, the Environmental Protection Agency intervened. The pipe that dumped waste water from the canneries was moved out to the open ocean, and the coral started coming back. When Birkeland originally visited the reef in the late 1970s, there had been no Acropora. As the fastest growing coral, Acropora is common on new or recovering reefs.

“It’s a good indicator of if things are doing well or not because [Acropora is] also the most sensitive coral. It doesn’t defend itself or even repair itself. It’s just streamlined for growth … so, when it came back, it was a really good sign,” he said.

“The transect shows us that we can do something right now,” Birkeland said. The problem of global warming can be overwhelming, but there are local problems we can solve in the short term.

“We are all part of the global problem and the global solution. Contact politicians. Don’t step on living coral. Corals are only as thick in living tissues as the skin that covers your nose cartilage, yet they make reefs that are thousands of feet deep, cover entire islands,” Birkeland said.

Many islands in the Pacific, such as the Marshall Islands, would never have risen above sea level if not for coral, which covered the underwater land masses in such quantities that they broke the surface of the water, forming islands. 

“Coral reefs are more important to the world than people realize, and local efforts are key to their protection and maintenance,” Birkeland said.