In 2016 I found myself two miles below the surface of the Indian Ocean, gently drifting across what could have been another planet.
Alex Rogers is the Science Director of REVOcean, a new philanthropic organisation seeking solutions for a healthy ocean. He has spent the last 30 years studying the biodiversity of the deep ocean and has just published The Deep: The Hidden Wonders of Our Oceans and How We Can Protect Them.
We were greeted by a large pink shrimp, the swimmers under its tail rhythmically paddling the animal forward to investigate our vehicle with long antennae. Life appeared sparse, though the fine mud was dotted with burrows and riddled with scrapes and prints – signs of small creatures living in the seabed.
In much of the deep sea, dead plankton and other organic material has to descend from the ocean’s surface and most is consumed before reaching the bottom. It is a food-limited environment, but this does not mean it is barren. The muddy seafloor of the continental slopes is one of the most species-rich ocean ecosystems.
The hot fluids pouring out of the vents are rich in chemicals that are oxidised by bacteria to produce energy. Deep-sea crabs grow the bacteria on their hairy bellies and comb them off as food, while snails house the bacteria in a special organ in their body – the bacteria get a comfortable place to live and the snails are fed by them. Our discovery of the rich communities of unknown species around Antarctic vents changed the understanding of the distribution of life on vents globally and we now know that there are eleven distinct types of vent fauna.
Seamounts – sub-marine mountains – are another oasis of life. They trap animals participating in the largest migrations in the world – vertical daily migrations of twilight zone animals. Interactions between currents and the elevated seafloor block the animals from migrating away from the ocean surface as the sun rises, leading to high concentrations of food, attracting ocean predators, including tuna, sharks, whales, seals, seabirds and even turtles.
They also host species-rich cold-water coral reefs, as well as coral gardens and sponge beds. I led the first expedition to explore a coral seamount in sub-Antarctic waters in the southern Indian Ocean. Here, we found an extraordinary stony coral reef, but our delight rapidly turned to dismay and then anger when we discovered a lost fishing net that had scraped clear a large area of coral, with the broken and smashed branches still rolled up in its mesh.
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