Large parts of Australia’s Great Barrier Reef are again densely populated by corals than they have been in 36 years. Researchers from the Australian Institute of Marine Sciences (AIM) were able to determine this with the help of a long-term monitoring program in the northern and central areas of the largest reef on earth. In the southern region, on the other hand, large swarms of the crown-of-thorns starfish are causing problems for the corals, according to the institute’s annual report, which has just been published. The red echinoderms eat hard corals en masse.
In total, the scientists examined 87 representative reefs between August 2021 and May 2022. The result: north of Cooktown, the average hard coral cover increased from 27 percent last year to 36 percent. In the central area, the growth increased from 27 to 33 percent. In the southern part between Proserpine and Gladstone, however, only a coral cover of 34 percent was recorded, after 38 percent in the previous year.
Despite the partly good news, the AIM experts did not give the all-clear. The main reason for the increase is the fast-growing hard corals of the genus Acropora. “These corals are particularly vulnerable to wave damage caused by high winds and tropical cyclones,” said AIM program manager Mike Emslie. In addition, be the genus Acropora also extremely vulnerable to the coral bleaching that occurs when water temperatures rise. “This means that large increases in hard coral cover are quickly offset by disturbances on reefs where Acropora– corals predominate, can be annihilated.”
Disorders are now becoming more frequent and lasting longer, said institute director Paul Hardisty. This year’s coral bleaching was the fourth in seven years – absolutely “new territory” even for experts. Scientists have yet to understand how the reef responds to temperature stress and such frequent bleaching. Before 1998, the occurrence of such mass bleaching was not known at all.