Localized cyclone strike and flooding stress on the Great Barrier Reef likely to have far-reaching effects.
Australian floods bathed Great Barrier Reef corals in sediment while cyclone damage in one region may reduce reef growth elsewhere.
Coral reef managers see local stress from runoff an easier fix than bleaching from warming or carbon-emission caused acidification.
The devastation from summer monsoon flooding and Cyclone Yasi over Queensland, Australia, currently stands in the billions of dollars, while offshore the effects on the Great Barrier Reef are just beginning to be seen.
"Expected damage will include smashed coral beds, movements of coral boulders, sand and rubble and major disturbance to seagrass beds," announced the Great Barrier Reef Marine Park Authority in a statement following Yasi's category 5 cyclone strike on Feb. 5, 2011.
While the coastlines off of Whitsundays, Port Douglas, and Cairns are again open for tourism, the destructive winds tore through approximately 13 percent of the 1,400 mile-long (2,300 km) Marine Park said Great Barrier Reef Marine Park Authority Chairman Russell Reichelt in a press release on Feb. 10.
The floodwaters and cyclone have flushed sediment, as well as remnants of fertilizers and pesticides over the coral reef. The acidic terrestrial washout will leave telltale signs in the corals' skeletons for years to come.
In the short-term, too much sediment turns the normal nutrients in the water into an unhealthy diet. The corals' soft-bodied tissues, alive with photosynthetic organisms called zooxanthellae, normally rely on sunlight as their energy drink, but sunlight can't easily penetrate the sediment clouds. For their solid meals coral polyps feed themselves with tentacles, which grab planktonic organisms drifting by – but the washout muddies the waters into a mix where even the tiniest of particles are more likely to be sand and dirt rather than food. Like tree rings the skeleton growth during this period will reflect the stress of the flooding.
Still, the main threat to coral reefs remains climate change. Because weak cyclones are a regular feature of coral reef systems, it's the increase in intensity rather than frequency that is cause for concern, says Katharina Fabricius, principal research scientist with the Australian Institute of Marine Sciences (AIMS).
Between 1970 and 2005 Australia's Great Barrier Reef saw 116 cyclones cross its path, none of which were category five. Since 2006, three cyclones -- Larry, Hamish, and now Yasi – have tackled the coastline with category-five strength, dislodging large coral heads, the older corals in the reef.
"Reefs take 10 years in the most favorable conditions, and up to 50 years in deeper water to recover, so the presently high frequency of disturbance doesn't give the reefs sufficient time to recover, and consequently coral cover is declining," Fabricius told Discovery News.
Even if only a part of a reef is directly hit by a storm, as was the case with Cyclone Yasi, the impact can have a far-lasting reach. "They're not all completely isolated and separate, there is this communication between them," marine geologist Michael Field of the U. S. Geological Survey and project chief for the Pacific Coral Reef Project told Discovery News. He's referring to the millions of larvae that coral spawn which can travel in surface waters for hundreds of miles before settling and starting new coral colonies.
"If you lose a reef, you've lost one source," Field said. And that may be the source that feeds another reef somewhere else, he explained.
Because the Great Barrier Reef was already suffering from climate change related threats -- including bleaching from increased warming, and acidification from increased ocean absorption of atmospheric carbon dioxide -- it's hard to tell just how long the reef will take to recover from this year's specific incidents of flooding and cyclone damage.
Many coral reef scientists and managers are now taking the approach of managing what they can at the local level, says Field. "If we cannot practically address the acidification and the warming issues, then what we can do, what we must do, is control the other stresses that affect coral reefs," he said.
"Rivers carry four to 10 times more nutrients and sediments than they used to do in the past, this has to be curbed," Fabricius said. "No farmer wants to lose their top soil or fertilizer or pesticides, so keeping the stuff on the land where it does a lot of good and preventing it from entering the Great Barrier Reef where it does a lot of damage is an obvious target for action."
By mitigating the damage from other sources, scientists hope not only to better preserve coral, but also to give all coral reefs the best possible chance of surviving damage from climate change.