Parts of the Great Barrier Reef have recorded their highest amount of coral cover since records began 36 years ago, according to a new survey by the Australian Institute of Marine Science (AIMS). It isn’t all good news, however. Some regions of the reef have suffered further declines and scientists are still concerned that this delicate ecosystem is still in a deeply precarious situation.
The AIMS survey found that coral cover in the northern and central Great Barrier Reef has increased by 9 percent and 7 percent respectively, since 2021. Meanwhile, the average coral cover in the southern region decreased from 38 percent in 2021 to 34 percent.
The promising results suggest that the Great Barrier Reef has, to some extent, managed to bounce back from the significant number of mass bleaching events in recent years, the most severe of which happened in 2016 and 2017.
Bleaching occurs when the corals become stressed due to temperature, light, or nutrient changes. Single-celled algae live within corals in a symbiotic relationship: the coral provides shelter while the algae provide sugars through photosynthesis. Under stress, however, the algae jump ship and evade the coral, stripping it of vital nutrients and coloring, leaving it a ghostly white.
Even this year has seen a bleaching event, which was particularly concerning as it was the first to occur during a La Niña, a weather phenomenon that typically brings cooler water temperatures. Fortunately, however, it doesn’t appear to have been as devastating as in previous years.
“In our 36 years of monitoring the condition of the Great Barrier Reef we have not seen bleaching events so close together,” Paul Hardisty, chief executive of AIMS, said in a statement.
“Every summer the Reef is at risk of temperature stress, bleaching and potentially mortality and our understanding of how the ecosystem responds to that is still developing," added Hardisty.
“The 2020 and 2022 bleaching events, while extensive, didn’t reach the intensity of the 2016 and 2017 events and, as a result, we have seen less mortality. These latest results demonstrate the Reef can still recover in periods free of intense disturbances.”
Much of the increase in cover is being driven by fast-growing Acropora corals, says AIMS monitoring program team leader, Dr Mike Emslie. While the growth is welcome, these are not the hardiest of corals and it could leave the reef in a vulnerable place in years to come.
“These corals are particularly vulnerable to wave damage, like that generated by strong winds and tropical cyclones,” he explained. “They are also highly susceptible to coral bleaching, when water temperatures reach elevated levels, and are the preferred prey for crown-of-thorns starfish. This means that large increases in hard coral cover can quickly be negated by disturbances on reefs where Acropora corals predominate.”
It’s good news for now, but the Great Barrier Reef is not out of the woods yet. With climate change warming the planet’s oceans, we can expect to see some more bumpy years ahead, to put it lightly.
“The increasing frequency of warming ocean temperatures and the extent of mass bleaching events highlights the critical threat climate change poses to all reefs, particularly while crown-of-thorns starfish outbreaks and tropical cyclones are also occurring. Future disturbance can reverse the observed recovery in a short amount of time,” Emslie warns.