An ancient coral community prior to the European settlement of its neighboring continent lies beneath the sparkling waters off the coast of the Palm Islands of Australia.
This community of giant corals has just become known as the widest coral in the Great Barrier Reef, in fact, with an impressive length of 10.4 meters (34.1 feet).
Called Muga sin (Big Coral) of the traditional custodians of the Islands, the people of Manbarra, this magnificent and flourishing lattice of lattice calcium carbonate is inhabited mainly by the colony of living coral polyps that built it for many generations.
“The great Porites the coral on Goolboodi Island (Orpheus) is unusually hardy and resilient, ”James Cook University marine ecologist Adam Smith and colleagues write in their article.
“It has survived coral bleaching, invasive species, cyclones, severely low tides and human activities for nearly 500 years.”
While the flanks of the coral are still home to their creators along with their algae symbiotes, the zooxanthellae, part of its upper part is hollow.
Instead, the green and boring sponge (Cliona viridis), algae and even other types of corals (Acropora i Montipora species) have been established here: their competition for the remaining space draws clear lines on the skeletal surface of the coral.
Muga sin and its inhabitants. (Smith et al., Scientific Reports, 2021)
These sponges are often found on the more turbulent side of corals, where they are exposed to larger currents to facilitate filtering of water for bacteria and other microbes to eat.
“Sponge advances are likely to continue to compromise the size and health of colonies,” the researchers warn.
Sections of coral tissue can die due to exposure to the sun at low tide or warm water, without killing the entire colony, Smith and the team explain.
Under stress, jellyfish-like coral polyps upside down expel photosynthesizing zooxanthellae. This may allow them to conserve energy in the short term, but if the algae do not return, the polyps will soon starve, which is what happened to entire reefs during the recent devastating coral bleaching events.
The parts of the coral that are still alive reflect the cumulative and intergenerational effect of beneficial and destructive environmental factors.
Anatomy of a coral polyp. (NOAA)
Discovered in March during a citizen science project, at a depth of 7.4 meters (24.3 feet) on a slope of sand reefs, Muga sin it is also the sixth tallest coral measured at the Great Barrier Reef, with a height of 5.3 meters (17.4 feet). Depending on the height of the colony, the team estimates that it is between 421 and 438 years old.
They also found high-density “stress bands” recorded in the coral structure, evident since 1877, that appear significantly more frequently according to anthropogenic global warming.
But by reviewing significant environmental events since at least 1575, researchers learned that this coral community is very harsh, as it has survived nearly 100 bleaching events and up to 80 major cyclones during its lifetime, as well as the decreased water quality due to sediment runoff.
Muga sin belongs to the genus of stony corals called Porites, along with 16 other species found in the Great Barrier Reef. They are one of the most important types of corals that build reefs: they provide shelter with their large structures that other corals use.
Given the bleak future corals they face, thanks to ocean acidification and anthropogenic global warming (mainly due to these 20 and 100 companies), researchers think we can learn a lot from monitoring of this resistant colony.
The good news is that Smith and his colleagues found no signs of disease or coral bleaching. Muga sin. For now, this amazing coral city chonk is still full of life, with 70% of coral habitats alive.
If we take the actions recommended by scientists, there is still the possibility of keeping this ancient community alive for many more years.
This research was published in Scientific reports.