What is happening to the most remote coral reefs on the planet?

In the middle of the Indian Ocean are some of the last wild coral reefs on the planet. The Chagos Archipelago, a collection of atolls, the largest of which on Earth – the Great Chagos Bank – is home to reefs that have not been disturbed by humans for the past 50 years. Some estimates indicate that the Chagos Archipelago may contain more than half of the healthy coral reefs remaining throughout the Indian Ocean. These reefs are protected both by their remote location and in one of the largest no-harvest marine reserves in the world – the British Indian Ocean Territory Marine Protected Area (BIOT).

In 2015, scientists from the Khaled bin Sultan Living Oceans Foundation (KSLOF) came to the Chagos Archipelago to assess the condition of the reefs. During two months at sea, an international team of scientists conducted thousands of surveys of benthic and reef fish communities at more than 100 sites across the archipelago. This research was conducted as part of the Foundation’s Global Reef Expedition (GRE), a 5-year research mission that traveled around the world to assess the health and resilience of coral reefs.

“The Global Reef Expedition was designed to assess the state of benthic and reef fish communities and assess the impact of anthropogenic and natural disturbances on coral reef ecosystems,” said Alexandra Dempsey, Director of Management KSLOF scientist and one of the authors of the report. . “A priority for us was to study reefs with minimal human disturbance, and there was no better place on Earth to do so than the Chagos Archipelago.”

Their findings are detailed in a new report, the Global Reef Expedition: Chagos Archipelago Final Report, which contains detailed information on the diversity and abundance of corals and reef fish species as well as valuable background data on the state of reefs at any given time. .

What they found during the search mission were reefs with an astonishing diversity of corals and an abundance of fish. Of all the reefs surveyed on the Global Reef Expedition – the largest coral reef mapping study and expedition in history – the reefs in the Chagos Archipelago were among the most diverse and had some of the highest coral cover. and fish biomass. They also had more fish per square meter than in any country studied on the GRE.

“When we first arrived in the Chagos Archipelago, the reefs were beautiful,” said Renée Carlton, marine ecologist at KSLOF and lead author of the report. “We saw reefs covered with a diverse assemblage of living corals and surrounded by an astonishing abundance of fish. It was refreshing to see such flourishing reefs.”

However, even here, in what are perhaps the most remote and best protected reefs on the planet, there were signs of human impacts. Towards the end of the research mission, KSLOF scientists witnessed the start of what would become a catastrophic, global mass coral bleaching event, illustrating the extent of the coral reef crisis. The data in the report released today is the latest data collected in the Chagos Archipelago before this disastrous bleaching event resulted in mass coral kills on the reefs.

“Of all the reefs visited on the Global Reef Expedition, those in the Chagos Archipelago were certainly the most remote and least disturbed,” said Sam Purkis, Chief Scientist of KSLOF as well as Professor and Head of the Department of marine geosciences of the University. from the Rosenstiel School of Miami’s Marine and Atmospheric Science. “Witnessing a coral bleaching event during our research mission was heartbreaking, but there is compelling evidence that reefs that are untouched by direct human pressures such as overfishing and coastal development, have magnified resilience, so there was hope that the archipelago would rebound. to health relatively quickly. “

At the first signs of bleaching, corals in the Chagos Archipelago took on shades of pink, blue and cotton candy yellow before turning white, as corals tried to shield themselves from the sun’s harmful rays afterwards. have lost their symbiotic algae. As the warm waters persisted, the extent of the bleaching was evident and affected the vast majority of shallow corals. A study shortly after the bleaching event found living coral plummeted from the relatively healthy 31-52% seen on the Global Reef Expedition to just 5-15%. Since then, there have been promising signs of reef recovery, but the reefs are unlikely to have returned to the same condition they were before the bleaching.

The report released today will provide marine managers with information on what reefs looked like before the devastating bleaching event, so that changes to the reef can be tracked over time and monitor how the ecosystem is performing. restores. The Foundation shared the report with representatives of BIOT’s Marine Protected Area (MPA) as well as scientists and conservation organizations invested in the preservation of these remarkable reefs.

The Global Reef Expedition mission to the Chagos Archipelago allowed scientists to study some of the most intact coral reefs in the Indian Ocean. Their results illustrate what reefs can be like when protected in large MPAs without harvesting, but they also highlight the dangers that all reefs face in a changing world.

Provided by Khaled bin Sultan Living Oceans Foundation