Sand deposits like this one at One Tree Island in the Great Barrier Reef can tell you how healthy a coral reef is, even from the air.
Global warming poses a major threat to coral reefs. If the water gets too warm, the corals die off and the previously species-rich reefs are like a graveyard. This is already happening worldwide. The Great Barrier Reef off Australia, the largest coral reef in the world, is also considered acutely endangered. When corals of such a reef die off, this is reflected in a bleaching of the corals, which is clearly visible in dives.
In the future, however, a glance will be enough to assess the health of a reef. Scientists from the University of Sydney have been studying how to read coral health from sand skirts, sand deposits along the shores of lagoons. Using the sand skirts, they can reliably estimate coral reef growth and carbonate sediment productivity — two important indicators of reef health. The new method makes the scientists' work much easier.
Previously, to check reef health, they had to “actively measure the chemistry of the water or take thousands of photos to calculate how much each creature in the ecosystem contributes to the productivity of the carbonate sediments,” explains Ana Vila-Concejo of the University of Sydney, who led the study.
The analysis of the sand aprons even allows a glimpse into the past. The researchers have determined that carbonate productivity in the southern Great Barrier Reef is now only half what it was in the past millennia. "Our results suggest that ecosystem health was much better then, so we're likely seeing the effects of climate change in our data today," Vila-Concejo said. By understanding the evolution of the sand aprons and thus the reefs, the scientists can better model the future effects of climate change and look into the future of the Great Barrier Reef.