Since the mid-1990s, coral on the Great Barrier Reef has declined by more than 50 percent, and it goes to almost every species, to every depth, and to every size, according to a new study.
The research covered the entire 2,300 kilometers of the Great Barrier Reef and found a disturbing loss at almost every level.
“A living coral population has millions of tiny, baby corals, as well as many large ones – the big mamas that make up most of the worms,” explains Andy Dietzel of the ARC Center of Excellence for Coral Reef Studies.
“Our results show that the Great Barrier Reef’s ability to recover – its stability – has been compromised compared to the past, because there are fewer babies, and fewer older adults breeding.”;
Like the old forests, these large corals are the most valued by marine scientists.
The loss of older corals like this can have a cascading effect on the entire reef system, as the largest colony in a population is disproportionately affecting the reproduction and genes of the next generation while also providing larger habitat and food for fish and other reef life.
“The global decline of large, mature trees, for example, indicates the loss of critical habitat, food, and carbon storage,” the authors write. But while the size of the forests on the ground has been carefully monitored in recent years, trends in coral size are rarely examined; traditionally about scope.
To fill this gap, researchers recorded a systematic decline in coral abundance on the Great Barrier Reef across size, habitat, sector, and taxa from 1995 to 2017. During that time, the reef experienced many locals. storm, four mass whitening events, and two major thorn-crown starfish outbreaks (not to mention another severe bleaching event that occurred this year).
The study of the vast expanse of the Great Barrier Reef was clearly a challenge, and to estimate the size of the colonies, the researchers used the length of the line to block as a proxy.
This means that a line is placed on the coral reef to measure the excess length of the various organisms below.
Although not a direct measure of coral size, line-intercept length may indicate changes in the underlying colony size, and since it has been used for a long time, the authors say it is “a no. convertible source of historical demographic data “on corals.
The authors found that an abundance of coral was strongly opposed to all colony sizes and all coral taxa. These changes are most pronounced in the Northern and Central regions of the Great Barrier Reef, where most recent coral mass bleaching has taken place.
“We used to think the Great Barrier Reef was protected by its excessive size,” says marine biologist Terry Hughes, “but our results show that even the world’s largest and relatively well-established reef system is increasingly compromised and going down. “
The loss of medium and large colonies is particularly troubling, as they can inhibit reproduction and prevent older corals from replenishing declining populations. At the same time, disproportionate loss in smaller colonies indicates a reduction in the propagation of small coral larvae.
“The potential for recovery of older fecund corals is uncertain given the increasing frequency and intensity of turbulent events,” the authors of the current study write.
“The systematic decline of smaller colonies in regions, habitats, and taxa indicates that a decline in recruitment has further eroded the potential recovery and stability of coral populations.”
And the window for recovery will close quickly. If we do not cut our emissions by the end of the century, studies show destructive bleaching events such as those that occurred in 2016 and 2017 that could occur on an annual basis.
“I think we can control the heating somewhere between 1.5-2 ° C [above pre-industrial levels], according to the Paris agreement, then we will still have a reef, “Hughes told The Guardian.
“But if we get to 3-4 ° C due to uncontrolled emissions, then we have no recognizable Great Barrier Reef. ”
The study is published in Royal Society Procedures B.