Coral reefs more resistant to seaweed than previously thought

June 2nd, 2009 - 3:53 pm ICT by ANI  

Washington, June 2 (ANI): A new study by a team of marine scientists from the US and Australia has suggested that coral reefs appear to be more resistant to seaweed than previously thought.

Their study is the first global-scale analysis of thousands of surveys of individual reefs - in all, more than 3,500 examinations of about 1,800 reefs performed between 1996 and 2006.

“Until now, many scientists have concluded that the world’s coral reefs are being overrun by seaweed,” said John Bruno of the University of North Carolina at Chapel Hill and lead author of the study.

“Our findings show that’s not the case. Seaweed have taken over and are dominating some reefs, but far fewer than assumed,” he added.

According to researchers, the problem with too much seaweed is that it can smother the baby corals, reducing the ability of reefs to recover from other disturbances such as hurricanes and disease outbreaks.

Over recent decades, there have been several dramatic examples of such shifts, with one of the most widely known and striking cases occurring in the Caribbean in the 1980s.

Bruno, along with colleagues Hugh Sweatman from the Australian Institute of Marine Science and William F. Precht, a Florida-based marine ecologist, set out to determine how bad and how widespread the problem of seaweed-dominated reefs really is.

The team came up with a “phase-shift index” to determine the state of each reef.

Pristine reefs where coral was still abundant had an index number of -2 to -3, while areas where macroalgae have overwhelmed reefs’ surfaces were given an index ranking of between 3 and 5.

They found that while there were moderate local increases in seaweed cover over the study period, only four percent of reefs worldwide were dominated by macroalgae - that is, more than 50 percent of a reef’s surface was covered in seaweed.

Researchers also found overall “phase shift severity” decreased in the Caribbean, did not change in the Florida Keys and the Indo-Pacific, and increased slightly on the Great Barrier Reef due to moderate coral loss.

“Overall, our results indicate that there is no general recent trend (i.e., post-1995) toward marcoralgal dominance,” according to the researchers.

“The results from this study question many of the prevailing paradigms that coral reef ecologists have developed over the past two decades,” Precht said. “These findings will change the way we view and manage these fragile yet resilient ecosystems,” he added. (ANI)

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