Recent findings published in the journal Coral Reefs show the that Halimeda bioherms in the deeper seafloor beyond the Great Barrier Reef cover a surprisingly vast area: 2,300 square miles, compared to what was previously thought of 800 square miles.
Halimeda is an algae that, when alive, is green. Yet when the algae dies, it turns into white, flaky limestone pieces that build up over a long periods of time — up to 10,000 years — and can make doughnut-shaped mounds 30 feet tall and 600 feet across.
One of the study authors, Robin Beaman of James Cook University, says in a press release, "We've known about these geological structures in the northern Great Barrier Reef since the 1970s and '80s, but never before has the true nature of their shape, size and vast scale been revealed."
The Australian team of researchers used laser imaging data that the Australian navy gathered by plane in order to make a 3-D map of the ocean floor. The LiDar images were worth the tedious flyovers: "When the three-dimensional shape of them was revealed, it was really surprising," lead author Mardi McNeil of the University of Queensland told ABC Australia. "They form these fields of doughnut-shaped structures ... sometimes they're like singular circular rings, sometimes in groups of three or four," she adds.
Associate Professor Jody Webster from the University of Sydney, said the revelations about the extent of the bioherm field make questions over its vulnerability to climate change even more pressing. “As a calcifying organism, Halimeda may be susceptible to ocean acidification and warming. Have the Halimeda bioherms been impacted, and if so to what extent?”
Beaman responds, stating that the discovery also opens up many other new avenues of research. “For instance, what do the 10-20 metre thick sediments of the bioherms tell us about past climate and environmental change on the Great Barrier Reef over this 10,000 year time-scale? And, what is the finer-scale pattern of modern marine life found within and around the bioherms now that we understand their true shape?”
He said future research would require sediment coring, sub-surface geophysical surveys, and employing autonomous underwater vehicle technologies to unravel the physical, chemical and biological processes of the structures.
