The Last Great Coral Reef Wilderness
Global Geneva Magazine
April 21, 2021
By Liz Thompson & Renée Carlton
Scientists aboard the Global Reef Expedition—the largest coral reef survey and mapping expedition in history—traveled to the Chagos Archipelago to study some of the most pristine coral reefs on Earth. What they found were reefs teeming with life, but also worrying signs of the unfolding coral reef crisis.
In the middle of the Indian Ocean lies the Chagos Archipelago, a collection of atolls and submerged banks where the reefs have been largely undisturbed by humans for the last 50 years. Located over 1500 kilometers south of India, the waters of the Chagos Archipelago are home to some of the most remote and undisturbed coral reefs on Earth. The reefs are protected by both their location and because they are found in one of the world’s largest no-take marine protected areas (MPAs).
The Khaled bin Sultan Living Oceans Foundation led a research mission to study these reefs in 2015 as part of the Global Reef Expedition. (See Global Geneva story). This scientific research excursion circumnavigated the globe to address the coral reef crisis and gain a better understanding of the health and resiliency of coral reefs in the Atlantic, Pacific, and Indian Oceans. Over the course of two months at sea, scientists aboard the Global Reef Expedition conducted thousands of surveys of the benthic and reef fish communities at over 100 locations across the Chagos Archipelago. Only a handful of research missions have had the opportunity to explore the reefs of Chagos, and some of the reefs visited on the Expedition had never been surveyed by scientists before.
One priority for the Global Reef Expedition was to study reefs with minimal human disturbance, and there was no better place on Earth to do that than the Chagos Archipelago. Some estimates indicate these reefs could contain more than half of the healthy reefs remaining in the Indian Ocean. Because of its remote location and protected status, Chagos was the perfect place to explore global issues such as climate change and overfishing that threaten the long-term survival of coral reefs. By studying these relatively pristine reefs, the scientists wanted to add to their knowledge about the coral reef crisis, and were eager to see how coral reefs could thrive without the impacts of these other major disturbances. (See Global Geneva story on the EPFL corals’ project in the Red Sea)
What they found in the Chagos Archipelago was a stark reminder that the coral reef crisis is affecting reefs everywhere, even in the last great coral reef wilderness area on Earth.
The scientific findings from the research mission were recently released in a new publication, The Global Reef Expedition: Chagos Archipelago Final Report, which contains detailed information on the diversity and abundance of corals and reef fish species along with valuable baseline data on the state of the reefs at a point in time.
When the research mission began, scientific divers found reefs teeming with life, a diverse assemblage of corals, and an abundance of fish. The reefs of the Chagos Archipelago were truly exceptional; they had some highest coral cover and fish biomass recorded on the Global Reef Expedition. The Chagos Archipelago was teeming with schools of jacks and snappers, swarms of small fish clung to the reefs, and large fish such as groupers, sharks, and rays were found in throughout the area. These large top-predators are reported to be much less common in the rest of the Indian Ocean, as they are highly vulnerable to fishing pressure, but they were thriving in the protected waters of Chagos.
In addition to having an impressive diversity of fish, Chagos had more fish per square meter than reefs in any of the 15 countries studied on the Global Reef Expedition. Chagos had an astounding abundance and diversity of life in the water and on the seafloor. However, towards the end of the research mission, the scientists witnessed the beginning of what would become a catastrophic mass global bleaching event.
In the clear and unusually calm waters of the Indian Ocean, the scientists watched the corals bleach before their eyes as they surveyed the reefs and fish communities. During the first signs of bleaching, corals in the Chagos Archipelago turned vibrant, almost neon-colored shades of pink, blue, and yellow before turning white, as the corals tried to protect themselves from the sun’s harmful rays after losing their symbiotic algae. As the warm waters persisted, the extent of the bleaching was readily apparent and impacted the vast majority of the shallow-water corals.
Although it was heart-wrenching to see this happen, previous studies had shown that reefs which are spared direct human pressures, such as through overfishing and coastal development, have increased resilience. There was hope that corals in the archipelago would bounce back to health relatively quickly. However, a study shortly after the bleaching event found live coral fell dramatically from the relatively healthy 31-52 per cent observed on the Global Reef Expedition, to only 5-15 per cent. Since then, there have been promising signs the reefs are recovering, but it is unlikely the reefs have, and may never, return to the same state they were in prior to bleaching. (See Global Geneva piece on saving Caribbean corals.)
Because the Global Reef Expedition was the last research mission to survey the reefs prior to the mass bleaching event, the Living Ocean Foundation’s findings will be extremely useful to marine managers as they assess the impact of the bleaching event and monitor how the reefs are recovering over time. This report on the state of the reefs can also help government agencies, conservation organizations, and scientists with the ongoing management and conservation of reefs in the marine reserve. In order to help make this science readily available to those who can use it, the Living Oceans Foundation has shared their findings with individuals and organizations invested in the reef’s recovery, and made the report freely available on their website at livingoceansfoundation.org.
The world has lost half of its coral reefs in the past 50 years, and is are set to lose even more in the future. With the increased frequency of coral bleaching due to a changing climate, combined with increasing human impacts such as overfishing and pollution, the reefs face an uphill battle to survive as we know them today.
To save reefs, large marine protected areas are the best tool we have. In the face of the coral reef crisis, which is threatening the survival of coral reefs across the planet, the reefs of the Chagos Archipelago face some of the best odds, despite recently bleaching. They are protected, relatively free from human influence, and still contain large and healthy fish populations and a stunning diversity of life. This diversity may be helping the reefs in Chagos recover from this bleaching event, but it may also be one of the key factors that could help these reefs survive well into the future.
The Global Reef Expedition mission to the Chagos Archipelago gave scientists the chance to study some of the most pristine coral reefs in the Indian Ocean. Their findings illustrate what remarkable places coral reefs can be when protected, but they also highlight the perils all reefs face in a changing world.