Recurring Occurrence of Crown-of-Thorns Starfish Causes Decline of Southern Section of Great Barrier Reef's Average Reef Cover

Since the Australian Institute of Marine Science (AIMS) started keeping track 36 years ago, the coral cover in the northern and central Great Barrier Reef has reached its greatest level.

However, continuing outbreaks of crown-of-thorns starfish caused the average coral cover in the southern area to decline.

While the Reef underwent its fourth significant bleaching episode in the past seven years this year, it was not as severe as previous instances, and was not anticipated to result in a significant loss of coral populations.

Highest coral cover

(Photo : Hiroko Yoshii/Unsplash)

Average hard coral cover grew to 33% in the Great Barrier Reef's central zone and to 27% in the region north of Cooktown between August 2021 and May 2022 as part of the AIMS Long-Term Monitoring Program (LTMP), which examined 87 representative reefs (from 26 percent in 2021), as per ScienceDaily.

On the other hand, the average coral cover in the southern area (from Proserpine to Gladstone) fell from 38% in 2021 to 34%.

The loss of coral cover in the southern area, according to AIMS CEO Dr. Paul Hardisty, demonstrated how dynamic the Reef was while the results in the north and centre regions revealed that the Reef may yet recover.

According to him, continuous outbreaks of crown-of-thorns starfish caused a loss of a third of the increase in coral cover we saw in the south in 2020/21 the previous year.

This demonstrates how susceptible the Reef is to the ongoing, severe, acute disruptions that are happening more frequently and staying longer.

The rising frequency of large coral bleaching episodes, with this year's occurrence being the fourth in seven years and the first to take place during a La Niña, is "uncharted ground," according to Dr. Hardisty.

They have not observed bleaching occurrences that closely spaced between in the 36 years that they have been keeping track of the health of the Great Barrier Reef, he claimed.

Their knowledge of how the ecosystem reacts to temperature stress, bleaching, and perhaps death that the Reef faces every summer is still emerging.

Although significant, the bleaching episodes in 2020 and 2022 weren't as severe as those in 2016 and 2017, which led to reduced mortality.

These most recent findings show that the Reef may still recover when there aren't any major disruptions.

The team leader of the AIMS monitoring program, Dr. Mike Emslie, stated that the 2022 results built on the improvements in coral cover reported for 2021, with the majority of the increase still being driven by Acropora corals, which have a rapid rate of growth.

Also Read: One of the Most Vibrant Coral Reef Systems in the World Faces a Dangerous Threat

Bleaching event

The biggest reef system in the world is thought to have seen significant coral loss as a result of warmer water temperatures, especially in February, as per BBC.

According to scientists, vast regions of severe damage, including widespread bleaching, have been found. But they have also located some prosperous areas.

Similar incidents in 2016 and 2017 devastated two-thirds of the reef.

Because of its "enormous scientific and intrinsic value," the reef system, which spans more than 2,300km (1,400 miles), has been designated a World Heritage site.

Due to the effects of human-induced climate change, Australia was compelled to lower its five-year reef prognosis from bad to very poor in 2019.

Two-thirds of the reef system was affected by the previous disasters, which wiped off coral colonies and destroyed homes for other marine creatures.

However, according to head scientist David Wachenfeld, this year's bleaching was only "moderate" in several important reefs for tourism in the northern and central areas.

This implied that the coral there would likely recover, he continued.

The reef is still an active, dynamic system, but overall, the harm from each subsequent occurrence has increased, according to him.

He argued that these occurrences should be viewed as worldwide demands for the most aggressive response to climate change.