Oceanographic drivers of ecosystem variability in the Chagos Archipelago

This is a four-year project, funded by £1,500,000 from the Garfield Weston Foundation and >£1,000,000 from the Bertarelli Foundation, to understand the physical processes that influence the ecosystems found throughout the Chagos Archipelago, a very large (640,000 km2) Marine Protected Area (MPA) in the Indian Ocean. For more than a decade, the area has been covered by a 640,000 km² MPA, which incorporates a no-take zone, meaning it has endured little negative impact in terms of day-to-day human activity. The remote location of the Chagos Archipelago means that there are minimal human impacts, and thus it is one of the most pristine marine environments on earth. However, as with the rest of the planet, it is being affected by climate change and has a legacy of fishing.

Our research will use this near-pristine environment as a planetary-scale laboratory to learn how a thriving marine ecosystem develops in its natural state. We will work to understand how mostly intact marine ecosystems function and explore how conservation practices put in place as part of the MPA might benefit other areas of the marine environment.

The research brings together oceanographers, marine biologists, hydrographic surveyors and biogeochemists from the University of Plymouth and the Manta Trust, an international charity established by Plymouth graduate Guy Stevens.

Our work, will target the pivotal roles played in the thriving Chagos Archipelago ecosystem by seamounts, deep “mesophotic” reefs, and regional-scale changes in oceanographic conditions. Our overall aim is to develop strategies for conserving the marine environment that accounts for the complex relationship between the biological and physical regimes. The specific environments we focus on in this project are those in greatest and most urgent need of conservation measures.

Firstly, many seamounts have been overexploited to the point of ecosystem collapse because of the enormously diverse range, and disproportionate abundance, of marine life that aggregates over and around them. Our research is focused around a seamount called Sandes, which hosts a huge aggregation of silvertip sharks around the summit. Scientists will look to establish what physical and oceanographic features cause this phenomenon.

Secondly, mesophotic coral reefs exist in the twilight zone between depths of 30-150 m. While these ecosystems have traditionally been studied to investigate their role as refugia for shallow-water reefs, they are biologically and ecologically significant ecosystems in their own right with high levels of biodiversity, including unique, rare and endemic species, that require protection.

Using a Remotely Operated Vehicle, scientists will document the diversity and distribution of mesophotic communities and how this varies with depth around Egmont Atoll and Sandes Seamount. They will also collect samples of corals to investigate the genetic connectivity of populations between shallow and mesophotic reefs.

Thirdly, scientists are undertaking the most comprehensive research to date of the reef manta ray subpopulation that is resident at Egmont Atoll in the Archipelago. Reef manta rays are listed as vulnerable to extinction on the IUCN’s Red List of Threatened Species. Measures to protect them are hindered by an incomplete knowledge of how manta use environmental cues to determine where and when they forage, often in dense aggregations that render them especially vulnerable to exploitation.

The conservation strategies we are developing will provide a cornerstone of measures designed to protect these charismatic animals but, equally, will contribute to equivalent efforts for other large marine animals.