Machines mining minerals in the deep ocean have been found to cause significant damage to life on the seabed, scientists carrying out the largest study of its kind say.

The number of animals found in the tracks of the vehicles was reduced by 37% compared to untouched areas, according to the scientists.

The researchers discovered more than 4,000 animals, 90% of which were new species, living on the seafloor in a remote area of the Pacific Ocean.

Vast amounts of critical minerals needed for green technologies could be locked in the deep ocean, but deep sea mining in international waters is very controversial and currently not permitted until more is known about the environmental impacts.

The research by scientists at the Natural History Museum in London, the UK National Oceanography Centre and the University of Gothenburg was conducted at the request of deep sea mining company The Metals Company.

The scientists said their work was independent and that the company was able to view the results before publication but was not allowed to alter them.

The team compared biodiversity two years before and two months after the test mining that drove machines for 80km on the seafloor.

They looked specifically at animals 0.3mm – 2cm in size, such as worms, sea spiders, snails and clams.

In the tracks of the vehicle, the number of animals fell by 37% and the diversity of species by 32%.

“The machine removes about the top five centimetres of sediment. That’s where most of the animals live. So obviously, if you’re removing the sediment, you’re removing the animals in it too,” lead author Eva Stewart, PhD student at the Natural History Museum and the University of Southampton, told BBC News.

“Even if they are not killed by the machine, pollution from the mining operations could slowly kill some less resilient species,” said Dr Guadalupe Bribiesca-Contreras from the National Oceanography Centre.

A few of the animals could have moved away, but “whether or not they come back after disturbance is a different question”, she added.

However, in the areas near the vehicle tracks, where clouds of sediment landed, the abundance of animals did not decrease.

“We were expecting possibly a bit more impact, but [we didn’t] see much, just a shift in which species were dominant over others,” Dr Adrian Glover, research scientist at the Natural History Museum, told BBC News.

“​We’re ​encouraged ​by these ​data,” a spokesperson for The Metals Company told BBC News.

“After ​years ​of ​activist ​alarm ​that ​our ​impacts ​would ​spread ​thousands ​of ​kilometers ​beyond ​the ​mine ​site, ​the ​data ​show ​that ​any ​biodiversity ​impacts ​are ​limited ​to ​the ​directly ​mined ​area,” they added. 

But some experts do not think that this is good news for mining companies.

“I think the study shows that current technologies for harvesting are too damaging to permit large-scale commercial exploration,” Dr Patrick Schröder, senior research fellow at the Environment and Society Centre at think tank Chatham House, told BBC News.

“These were only tests and the impact was significant. If they did that at large scale, it would be even more damaging,” he added.

Deep sea mining is controversial. At the heart of the debate is a difficult problem.

The latest research took place in the Clarion-Clipperton Zone, a 6m sq km area of the Pacific Ocean estimated to hold over 21bn tonnes of nickel, cobalt and copper-rich polymetallic nodules.

The world needs these critical minerals for renewable energy technologies to tackle climate change. They are essential components in solar panels, wind turbines and electric vehicles, for example.

The International Energy Agency predicts that demand for the minerals could at least double by 2040.

The minerals have to come from somewhere, but some scientists and environmental groups are gravely concerned that mining the deep seas could cause untold damage.

Some fear that before we have the chance to explore the full nature of life in the undiscovered deep ocean, it could be endangered.

Oceans play a critical role in regulating our planet and are already at severe risk from rising temperatures.

The International Seabed Authority (ISA), which governs activity in international waters, has not yet approved commercial mining although it has issued 31 licences for exploration.

A total of 37 countries, including the UK and France, are backing a temporary ban on mining.

This week Norway postponed mining plans in its waters including the Arctic.

But in April, US President Donald Trump called for domestic and international projects to be fast-tracked, as the US wants to secure the supply of minerals for use in weapons.

If the ISA concludes that current mining techniques are too destructive, companies could try to develop less intrusive ways of extracting nodules from the seafloor.

The research is published in the scientific journal Nature ​Ecology ​and ​Evolution.