‘The closest humans come to being a fish’: How scuba is pushing new limits

Scientists have begun to explore the ocean’s ‘middle light’ – the mesophotic zone, a lesser-known part of our seas – with new rebreathers

Divers explore under the Eureka oil rig platform at Long Beach California. The platform is 8 miles off the California coast and has an ecologically diverse ecosystem underneath

In between the sunlit shallows and the dark, deep ocean lies an inky realm where few people have ever been. Stretching from about 30 to 150 metres, the mesophotic zone (meaning 'middle light') is an awkward depth. It lies just beyond the reach of regular scuba divers and it’s usually what aquanauts inside multimillion-dollar submersibles merely glimpse as they plunge deeper.

However, a new generation of scientists is pushing the limits of diving to discover the secrets of this ecological zone. “There’s so much to see, and everything seems new. It’s like a different world,” says Erika Gress from James Cook University in Queensland, Australia.