(Bloomberg) — The mass death of young and old corals in Australia’s Great Barrier Reef is threatening the recovery of the largest living structure on Earth.
The bleaching of corals off Australia’s northeastern coast due to ocean warming and acidification is happening across all species and to specimens of all ages, according to a new study that analyzed coral demographics. The study, led by Andy Dietzel at the ARC Centre of Excellence for Coral Reef Studies in Australia, confirmed the Great Barrier Reef lost half its corals between 1995 and 2017.
“We measured changes in colony sizes because population studies are important for understanding demography and the corals’ capacity to breed,” Dietzel said in a statement. “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.”
Coral reefs are so sensitive to changes in ocean conditions that they have become a leading indicator for the collapse of the ocean ecosystem as climate change advances. Even if global warming is limited to 1.5°C from pre-industrial times —considered a best-case scenario— almost all warm-water coral reefs are forecast to suffer significant losses.
Oceans have absorbed 93% of heat captured by greenhouse gases since the 1970s. Their ability to capture and store carbon dioxide stopped keeping pace with emissions in the 1990s and their sponge-like capacity will keep diminishing even if humans manage to cut the greenhouse gas emissions that cause global warming.
Reefs are following a similar trend, Dietzel’s research found. Record temperatures that triggered three mass bleachings in the past five years, especially including the record event of 2016 and 2017, have led to the loss of all sorts of coral structures.
Together, the deaths of baby corals and of the large corals that produce most coral larvae are leading to smaller coral colonies. That deterioration is steeper in the northern and central areas of the Great Barrier Reef, but the report notes that the southern part of the reef was also exposed to record-breaking temperatures in early 2020.
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