NOAA Fisheries
A NOAA researcher swims in front of the huge coral in the Mariana Trench Marine National Monument
A team of NOAA divers documented a gigantic coral in the Mariana Islands Porites rus that lives inside an underwater volcanic caldera. Given its dimensions and growth rate, its age will be around 2,050 years.
At a time when coral bleaching, disease and habitat loss are increasingly common, a hidden giant defies all odds.
A majestic cathedral-like structure built by a large number of colonies of Porites rusa species of stony coral, rises from a submerged volcanic caldera in the Maug Islands, in the Mariana archipelago.
“This coral was so big that, in fact, we can’t measure it easily due to diving safety restrictions,” he said. Thomas OliverPhD and principal scientist at NOAA’s National Coral Reef Monitoring Program, at the North American ocean agency.
Although the existence of the choir was already known by the local populationNOAA scientists recently had the opportunity to make the first approximate measurements during the 2025 National Coral Reef Monitoring Program surveys.
Measurements suggest that the colony covers about 1.347 m²extending over more than 31 meters at the top and 62 meters at the base. At the top, it is wider than the length of two school busesand at the base it is equivalent to the length of four.
NOAA
Approximate scale of the coral colony
This is the biggest coral Porites ever registeredbeing approximately 3.4 times greater than the massive Porites coral colony reported in 2020 in American Samoa. But size is not the only impressive feature of this Porites rus: so is your age.
“It is difficult to determine the true age of this coral because it does not produce growth rings like other corals,” he explained. Hannah BarkleyPhD, and principal scientist for NOAA’s National Coral Reef Monitoring Program.
“We estimate, roughly, that the Porites rus grows outward approx. one centimeter per yearo, so it is possible to imagine that a colony of this size is very old.”
At this rate, the choir may have more than 2,050 years!
Se this coral is certainly special, the same can be said of the place where it is located: the Maug’s boilerlocated within the Mariana Trench Marine National Monument.
The Maug Caldera has intrigued scientists committed to protecting the oceans for decades — from seafloor mapping expeditions in 2003, through in-depth ocean chemistry studies in 2014, to coral reef monitoring program visits in 2017, 2022 and 2025.
The boiler is known as a “natural laboratory” due to its carbon dioxide vents. In a certain area, the gas bubbles up from the vents and creates acidic oceanic conditions, allowing scientists to study how organisms, such as corals, might react to these conditions in the future.
It should be noted that the acidic conditions only affect habitats located a few meters from the chimneys, having no impact on massive coral which thrives just a few hundred meters further.
“It is remarkable to observe both extremess — a resilient and thriving mega coral, and a dead zone next to the carbon dioxide vents — in the same area. Maug is truly a very special place,” said Barkley.
The Mariana Trench Marine National Monument was established in 2009 and protects elements of scientific interest, including coral reef ecosystems, submerged volcanoes and hydrothermal vents.
Os coral reef ecosystems play a fundamental role in the health of the oceans, on which we depend for stable weather patterns, food, coastal protection, among others. To the US economy alone, coral reef ecosystems are worth more than $3.4 billion.
