In 2016 I found myself two miles below the surface of the Indian Ocean, gently drifting across what could have been another planet.
Black, exfoliated ropes of basalt lay in irregular ridges on the seafloor. Between them were pools of white sediment, which dusted the rock and looked like snow when illuminated by the lights of the submersible. For the first time in my life I could see no evidence of human life, anywhere.
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.
There are oases in the deep ocean where large animals live in abundance. I will never forget our first view of the deep-sea hot springs or hydrothermal vents on the East Scotia Ridge, Antarctica. Out of the gloom, the lights of our remotely operated vehicle, Isis, picked out heaving piles of bone-white – and hairy – yeti crabs. There were also piles of large black snails, stalked barnacles, limpets and other creatures. Every species was new to science.
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.
On other seamounts on the same ridge we discovered ghost nets, some with very fine mesh, trapping lobsters and fish. Areas that had once been living coral reef were smashed to fragments by deep-sea trawlers. The fisheries had been targeting orange roughy, a species that lives to 150 years old and has a very low resilience to fishing. Orange roughy spawns in large numbers over seamounts and are easy targets for modern vessels with acoustic fish finders and accurate satellite navigation. The limitation of food in the deep sea causes life to grow slowly live a long time with low rates of reproduction. Some corals live for more than 4,000 years and one sponge has been estimated to live for 11,000 years. When these habitats are destroyed by fishing, they do not recover.
Fishing is not the only menace. Our investigations of these seamounts revealed another menace. All our sediment samples – from on and in many of the animals – contained microplastic fibres; plastic is now everywhere in the ocean, even in the deepest trenches. The deep sea is not immune to climate change. The effects of ocean warming will alter the production of food at the ocean surface and drive changes on the seafloor many kilometres below. Even hydrothermal vents are vulnerable as climate change alters the oxygenation of the ocean, which may in time affect vent species.
Yet despite these many threats, people are now contemplating mining the deep ocean, an activity that may target the abyssal plains, hydrothermal vents and even seamounts.It is critical that we learn more about the deep ocean - how life is distributed through it and what functions deep-sea species perform for the Earth’s biosphere and, ultimately, us. Less than 0.0001 per cent of the waters between the surface and seabed have been explored and only 0.002 per cent of seamounts. It is ridiculous to pretend that we can manage the environmental impacts of activities such as deep-sea fishing and mining with such a dearth of knowledge.
We urgently need to protect these biological hot-spots. Crucial negotiations, which include developing a legal framework for the protection of biodiversity in areas beyond national jurisdiction, are taking place at the United Nations in New York. We are also about to embark on the UN Decade of the Ocean, an international effort to explore the ocean and better understand it. Until we have improved our knowledge of the deep ocean, new extractive activities such as deep-sea mining should be postponed.
Before 2019, only three people had been to the deepest part of the ocean: the Challenger Deep in the Marianas Trench in the western Pacific. This year, a new expedition allowed several more people to reach its depths. In comparison, 12 people have been to the moon. It is time to explore our inner space.
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