These vents have naturally acidified waters that hint at how our seas might change if atmospheric carbon dioxide levels continue to rise. They are conditions that would make it harder for corals and similar organisms to make the hard parts in their bodies.

Dr Jason Hall-Spencer's work suggests our oceans could lose perhaps 30% of their biodiversity this century. The Plymouth University researcher has been presenting his latest findings to a major conference in Vancouver, Canada.

"I am investigating underwater volcanoes where carbon dioxide bubbles up like a Jacuzzi, acidifying large areas of the seabed, and we can see at these vents which types of organisms are able to thrive and which ones are most vulnerable," he told the annual meeting of the American Association for the Advancement of Science (AAAS).

Dr Hall-Spencer treats the vents like a time machine. As he swims towards them, the pH level of the water falls and he can use particular locations to simulate what the open ocean will be like in the decades ahead if emissions of atmospheric CO2 go unchecked and much of the that gas is absorbed into sea.