How did the early Great Barrier Reef manage rapid environmental change?

April 30, 2024

As the modern Great Barrier Reef emerged after the last ice age, it had to cope with multiple environmental stresses – rising sea levels, increased sediment from a flooding coastline, ocean turbulence and likely warming oceans. It has been speculated that these factors inhibited the emergence of the modern Great Barrier Reef, but with little direct data. Their findings, published today in Quaternary Science Reviews, confirm a long-standing idea that elevated nutrient levels impacted reef growth. In modern coral reefs, nutrient-rich waters have been observed to favour macro algae, which can outcompete corals, as well as cause increases in bio-eroders that can weaken coral skeletons. “This provides evidence to understand early Holocene water quality on the southern Great Barrier Reef and demonstrates the capacity of the reef to grow under conditions that would typically be considered unsuitable.”

Jack-up drill system deployed on the reef flat with a blue star fish in the foreground.

As the modern Great Barrier Reef emerged after the last ice age, it had to cope with multiple environmental stresses – rising sea levels, increased sediment from a flooding coastline, ocean turbulence and likely warming oceans.

It has been speculated that these factors inhibited the emergence of the modern Great Barrier Reef, but with little direct data. Now, for the first time, geoscientists have managed to determine how these factors, particularly water quality, contributed to the reef’s development between about eight and six thousand years ago.

Their findings, published today in Quaternary Science Reviews, confirm a long-standing idea that elevated nutrient levels impacted reef growth. In modern coral reefs, nutrient-rich waters have been observed to favour macro algae, which can outcompete corals, as well as cause increases in bio-eroders that can weaken coral skeletons.

As the modern reef emerged thousands of years ago, scientists have found that these factors led to the establishment of slower-growing and more sediment-tolerant coral communities in deeper water, rather than the more familiar shallow and clear-water species that emerged later.

Senior author Professor Jody Webster from the School of Geosciences at the University of Sydney said: “This study has given us an historical picture of how the emerging modern reef responded to huge environmental stress.

“We get the picture of a dynamic ecosystem dealing with adverse environmental conditions during the early Holocene as sea levels rose and inundated the previously exposed shelf.”

Lead author Dr Kelsey Sanborn from the Geocoastal Research Group in the School of Geosciences said: “This work demonstrates that reef communities were able to grow despite higher sediment and nutrient input to the reef. However, the types of corals that grew were more like today’s inshore, turbid reefs, as opposed to the shallow and clear-water communities common on One Tree Reef today.

“This provides evidence to understand early Holocene water quality on the southern Great Barrier Reef and demonstrates the capacity of the reef to grow under conditions that would typically be considered unsuitable.”

The source of this news is from University of Sydney

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