Part of world's largest coral reef thriving in muddy waters
London: Scientists have found that a part of Great Barrier Reef, world's largest coral reef has been growing at a rapid rate in sediment-laden marine environments, a condition believed to be detrimental to reef growth.
Researchers led by the University of Exeter found that Middle Reef, part of Australia's iconic Great Barrier Reef has grown more rapidly than many other reefs in areas with lower levels of sediment stress.
Middle Reef is located just 4 kilometres off the mainland coast near Townsville, Australia, on the inner Great Barrier Reef shelf.
Unlike the clear waters in which most reefs grow, Middle Reef grows in water that is persistently 'muddy'. The sediment comes from waves churning up the muddy sea floor and from seasonal river flood plumes.
High levels of sediment result in poor water quality, which is believed to have a detrimental effect on marine biodiversity.
The research team collected cores through the structure of Middle Reef to analyse how it had grown. They used radiocarbon dating to map out the precise growth rate of the reef.
Results showed that the reef started to grow only about 700 years ago but that it has subsequently grown rapidly towards sea level at rates averaging nearly 1 cm per year.
These rates were significantly higher than those measured on most clear water reefs on the Great Barrier Reef and elsewhere.
The periods of most rapid growth averaging 1.3 cm a year occurred when the accumulation rates of land-derived sediment within the reef structure were also at their peak.
Although there is evidence that other reefs have suffered degradation from high levels of sediment, these findings suggest that in some cases reefs can adapt to these conditions and thrive.
The team believed this is because the accumulating sediment rapidly covers the coral skeletons after their death, preventing their destruction by fish, urchins and other biological eroders, thus promoting coral framework preservation and rapid reef growth.
"Our research challenges the long-held assumption that high sedimentation rates are necessarily bad news in terms of coral reef growth. It is exciting to discover that Middle Reef has in fact thrived in these unpromising conditions," Professor Chris Perry from the university said in a statement.
"It is, however, important to remain cautious when considering what this means for other reefs. Middle Reef includes corals adapted to deal with high sedimentation and low light conditions. Other reefs where corals and various other reef organisms are less well adapted may not do so well if sediment inputs increased," Perry said.
The study was published in the journal Geology.