Oct 14 2020
According to a recent study of the Great Barrier Reef, populations of its large, small, and medium corals have reduced in the last 30 years.
The Great Barrier Reef has lost half its corals in the past three decades. Diminished populations of the larger breeding corals mean there are fewer baby corals—which affects the reef’s ability to recover from the impacts of climate change. Image Credit: Andreas Dietzel.
Dr. Andy Dietzel, the study’s lead author from the ARC Centre of Excellence for Coral Reef Studies (CoralCoE), stated that while many studies have been performed across centuries relating to the changes in the structure of human populations—or, in the natural world, trees—no corresponding data is available on the changes in coral populations.
We measured changes in colony sizes because population studies are important for understanding demography and the corals’ capacity to breed.
Dr Andy Dietzel, Study Lead Author, ARC Centre of Excellence for Coral Reef Studies
Together with his co-authors, Dr. Dietzel evaluated coral communities and the size of their colony along the length of the Great Barrier Reef between 1995 and 2017. Their findings showed that coral populations have declined considerably.
We found the number of small, medium and large corals on the Great Barrier Reef has declined by more than 50 percent since the 1990s.
Terry Hughes, Study Co-Author and Professor, ARC Centre of Excellence for Coral Reef Studies
Hughes continued, “The decline occurred in both shallow and deeper water, and across virtually all species—but especially in branching and table-shaped corals. These were the worst affected by record-breaking temperatures that triggered mass bleaching in 2016 and 2017.”
The table-shaped and branching corals impart the structures that are crucial for reef inhabitants, for example, fish. The loss of coral population translates to a loss of habitat, which consequently decreases the abundance of fish population and the productivity of coral reef fisheries.
According to Dr. Dietzel, one of the significant implications of coral size is its impact on breeding and survival.
“A vibrant coral population has millions of small, baby corals, as well as many large ones—the big mamas who produce most of the larvae. Our results show the ability of the Great Barrier Reef to recover—its resilience—is compromised compared to the past, because there are fewer babies, and fewer large breeding adults,” added Dr. Dietzel.
According to the study’s authors, there is an urgent need for improved data on the demographic trends of corals.
If we want to understand how coral populations are changing and whether or not they can recover between disturbances, we need more detailed demographic data: on recruitment, on reproduction and on colony size structure.
Dr Andy Dietzel, Study Lead Author, ARC Centre of Excellence for Coral Reef Studies
Professor Hughes added, “We used to think the Great Barrier Reef is protected by its sheer size—but our results show that even the world’s largest and relatively well-protected reef system is increasingly compromised and in decline.”
Climate change has increased the frequency of reef disturbances, like marine heatwaves. The research work records a steeper decline of coral colonies in the Central and Northern Great Barrier Reef following the mass coral bleaching events that took place in 2016 and 2017. Moreover, the southern portion of the reef experienced record-breaking temperatures in early 2020.
“There is no time to lose—we must sharply decrease greenhouse gas emissions ASAP,” concluded the study’s authors.
Journal Reference:
Dietzel, A., et al. (2020) Long-term shifts in the colony size structure of coral populations along the Great Barrier Reef. Proceedings of the Royal Society B. doi.org/10.1098/rspb.2020.1432.
Source: https://www.coralcoe.org.au/