Coral Reefs

Robotic Diver Reveals the Secrets of Deep-Sea Tropical Reefs

Scientists working in the British Indian Ocean Territory hope their findings can help conserve shallow-water coral reefs

Shallow-water coral reefs are one of the world’s most important and diverse ecosystems. These tropical habitats are facing rapid destruction by human interference and ocean warming but they may have a hidden saviour deeper below the surface: mesophotic reefs.

Lying at depths of up to 150 metres, these remote marine ecosystems have remained largely unexplored for decades. But now a team of University of Plymouth scientists, led by Nicola Foster, are using a robotic submersible to gather coral samples from mesophotic reefs in the isolated British Indian Ocean Territory (BIOT). They hope to identify whether these reefs can play a role in supporting shallow-water corals. A new video reviews this vital research.

“When we first descended below 60metres we were amazed at the colourful abundance of life,” says Foster. “It was an incredible privilege to be one of the first people to see these reefs and all the life they support”.

Uncovering hidden species

The team had hoped to find that mesophotic corals are genetically related to shallow-water corals. If this is the case, they could help repopulate damaged reefs in shallower waters. Video footage to date has revealed very few coral species that inhabit both reefs, and it seems unlikely that they are closely related.

However, whilst genetic analysis continues, the research is revealing other uplifting insights into mesophotic reefs.

“We’ve discovered extensive, diverse coral communities that are positively thriving between 40 and 150 metres,” says Foster. “These reefs host huge biodiversity and potentially rare and endemic species.

“Like shallow-water reefs, mesophotic reefs support the marine ecosystem by providing food, regulating climate, offering essential nursery habitats and providing shoreline protection. It’s vital that we protect the mesophotic reefs to maintain the support they provide to shallow-water reefs.”

Their ongoing research to reveal the reefs’ secrets ties closely into the Bertarelli Foundation’s recent seminar ‘Secret Biodiversity: Uncovering Hidden Species and Behaviours’.

Deep diving

The state-of-the-art remotely operated vehicle (ROV) the team are using to survey the reefs is equipped with on-board lights and a camera system which streams high-resolution video to a surface unit on the boat. This means researchers can observe coral communities in real-time at depths where sunlight is limited. Capable of diving to depths of up to 1,000 metres, the ROV is also able to collect biological samples using its manipulator arm.

The ROV is especially useful for exploring mesophotic reefs in the BIOT MPA; because of its remoteness, human divers are not able to dive more than 25 metres below the surface.

A united effort across British Indian Ocean Territory

As part of the Bertarelli Foundation’s Marine Science Programme, Foster’s team share data and collaborate with other experienced researchers from a range of disciplines.

“We’re planning another cruise,” says Foster. “We’ll be documenting where mesophotic reefs occur within the MPA and describing their diversity. We want to see how they connect with shallow reefs and with other mesophotic reefs around the Chagos Archipelago and the wider Indian Ocean.”

The Bertarelli Foundation and the Garfield Weston Foundation fund this research as part of the Bertarelli Marine Science Programme.