A researcher swims over dome-shaped structures at the top of the coral structure (right). Credit: NOAA Fisheries.
A team of U.S. scientists has identified one of the largest coral colonies ever recorded, a massive organism stretching more than 100 feet (30 meters) across in the remote waters of the Mariana Islands, offering rare insight into marine resilience at a time of accelerating climate threats.
The coral, a species known as Porites rus, was documented during a 2025 expedition led by the National Oceanic and Atmospheric Administration (NOAA). Researchers found the colony inside the submerged volcanic caldera of Maug, part of the protected Mariana Trench Marine National Monument.
Measuring approximately 14,500 square feet (1,347 square meters), the coral’s massive structure makes it one of the largest single coral colonies known to science. Its size is so extraordinary that divers were unable to capture its full dimensions during a single dive due to safety limitations.
“This coral was so big, we actually couldn’t easily measure it,” said Thomas Oliver, a chief scientist with NOAA’s National Coral Reef Monitoring Program, in his statement, March 2026.
What Is the Giant Coral Found in the Mariana Islands?
The newly documented coral belongs to Porites rus, a species known for forming large, dome-like colonies in tropical waters. However, scientists say the size of this particular specimen far exceeds what is typically observed.
Unlike coral reefs, which are made up of many colonies, this structure is a single living organism composed of countless tiny polyps working together. Over centuries, these polyps secrete calcium carbonate skeletons, slowly building vast, rock-like formations.
The coral’s base spans nearly 200 feet (about 60 meters), with a height of more than 20 feet (6 meters), making it not only massive but also structurally complex. Its surface supports a wide array of marine life, from fish to invertebrates, effectively functioning as a micro-ecosystem.
Researchers say discoveries like this challenge assumptions about the limits of coral growth and longevity, especially in environments previously considered marginal for reef development.
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How Old Is the 100-Foot Coral Colony?
Determining the precise age of the coral has proven difficult. Unlike some coral species, Porites rus does not produce clear annual growth bands that can be easily counted.
Instead, scientists estimate its age based on average growth rates. Coral of this type typically grows about one centimeter per year. Given its enormous size, researchers believe the colony could be more than 2,000 years old.
If confirmed, that would mean the coral began forming long before the modern era, potentially dating back to a time when ancient civilizations were just beginning to rise.
“This is likely one of the oldest living coral structures in the region,” said Hannah Barkley, a scientist involved in the research.
Such longevity underscores the coral’s ability to survive natural environmental fluctuations over centuries — a trait scientists are keen to understand in the face of modern climate stressors.
Why This Discovery Matters for Coral Reef Conservation
The discovery comes at a critical moment for coral reefs worldwide. Rising ocean temperatures, acidification, and pollution have triggered widespread coral bleaching and mortality in recent decades.
Against this backdrop, the Maug coral represents a rare example of resilience.
“It’s a bright spot,” scientists say, highlighting the possibility that some coral systems may possess natural resistance to environmental stress.
Understanding what allows this coral to survive — whether genetic factors, location, or water chemistry — could inform conservation strategies aimed at protecting and restoring vulnerable reefs.
Coral ecosystems are essential to ocean health. They support roughly 25% of all marine species, protect coastlines from erosion, and sustain millions of people through fisheries and tourism.
Yet despite their importance, scientists warn that most coral reefs could face severe decline if global warming continues unchecked.
Extreme Ocean Conditions Near the Mariana Trench
One of the most intriguing aspects of the discovery is its location.
The coral lies within the Maug caldera, an underwater volcanic crater that contains active carbon dioxide vents. These vents release CO₂ into the surrounding water, creating localized conditions similar to ocean acidification — one of the major threats linked to climate change.
Just a short distance from the thriving coral colony, scientists observed areas where marine life was largely absent due to high acidity levels.
The stark contrast between these two environments — a thriving coral and a nearby “dead zone” — offers a unique natural laboratory for studying how ocean chemistry affects marine ecosystems.
“It’s remarkable to see both extremes in such close proximity,” Barkley said.
Researchers believe this setting could help scientists better predict how coral reefs will respond to future changes in ocean conditions.
Protected Waters Offer Hope for Survival
The coral’s location within the Mariana Trench Marine National Monument may be a key factor in its survival.
The monument is one of the largest marine protected areas in the world, limiting human activities such as fishing and resource extraction. This protection reduces local stressors, allowing ecosystems more space to adapt to broader environmental changes.
Scientists are now working with local communities, including Indigenous Chamorro and Carolinian groups, to better understand and protect the site. Plans are also underway to give the coral a culturally appropriate name.
While the discovery does not change the overall trajectory of coral reef decline globally, it provides valuable insight — and a measure of hope.
For researchers, the massive coral in the Mariana Islands is more than just a scientific curiosity. It is a living archive of ocean history, and potentially, a guide to its future. (Wage Erlangga)
