Skip to main content

Have you ever been at sea, on a boat, far from the coast, with the ocean as far as the eye can see? For those who have experienced it, the sensation of immensity is striking – the immensity of the ocean, this mass of water that seems to expand infinitely. And suppose one gets the chance to jump from the boat to immerse themselves. In that case, the same sensation of immensity appears underwater: a vertiginous sensation offered by the kilometers of this blue liquid extending below. 

If you have not experienced it, let’s try to picture it. The ocean is a huge space, in all its dimensions. The ocean is wide: it covers about 70% of the surface of the Earth. But the ocean is also really deep: the space underwater extends to 4,000 meters on average and up to 11,000 meters in the Mariana trench. In that regard, the ocean offers 98% of the habitable space on Earth. 

The immensity of the ocean makes it hard for us humans to explore and understand all of it. Although we have been able to explore mostly all of its surface, we have barely explored its depths – we actually know more about the surface of the moon than the bottom of the ocean. 

In a previous article, we focused on coastal ecosystems: coral reefs, mangrove forests, seagrass meadows and kelp forests; their importance for life in the ocean and from a climate change perspective. But coastal ecosystems are what their name suggests: they are found on the coast, in relatively shallow waters. So, what else is there in the rest of the ocean, in this wide and deep space? 

As inconceivable or unimaginable as it could appear, the deep ocean is actually full of life. In the dark and high-pressure water, various forms of life are thriving. Unfortunately, today, deep-sea ecosystems are seriously threatened. Right now, one of the biggest threats to life in the ocean is taking place, out of sight from most of us: humans are starting to mine the ocean bottom, putting unprecedented pressure on marine life. 

Let’s dive into the depths of the ocean to discover the hidden life found down below, the current threats which could eradicate deep-sea species and what we should do about it. 

Life in the deep ocean

First of all, let’s define the setting in which we are immersing ourselves. We are talking about the deep ocean, also called the deep sea. The deep sea starts after 200m but is on average 3,000-4,000 meters deep. Down there, it is dark as the light does not penetrate further than 200 m down. For the same reason, it is also pretty cold. The pressure is enormous, around 400 times more than the pressure felt at sea level. Basically, the conditions are highly different from what we can see or experience in shallow waters. 

These conditions seem to be the perfect hostile combination to prevent life to thrive. It even gave rise to the azoic (« lifeless ») theory proposed by Forbes in the 1840s, stating that the amount of life in the ocean would decrease with depth and that there would be none below 600m. And yet, many scientific explorations have shown us that the deep sea has a variety of ecosystems harbouring many forms of life. Species have adapted to live down there and their ways of growing, developing, moving and reproducing are conditioned by these specific deep-sea conditions. For example, at these depths, life develops really slowly (an important point for what will follow later on).

In this dark and cold space are found various ecosystems such as the abyssal plains, the seamounts and the hydrothermal vents. 

The abyssal plain is a flat area where species mostly live in sediments. Representing most of the ocean bottom, it is considered one of the biggest ecosystems on Earth in terms of surface area.

The seamounts are underwater mountains created by volcanic activity. They can be 1,000-3,000 meters high but never reach the surface (or they would be considered islands). 

Hydrothermal vents are geological formations from which heat and chemicals from the interior of the Earth are expelled. 

These ecosystems are hotspots of biodiversity, providing critical habitats for many species of corals, fish, molluscs, crustaceans and mammals that come here to grow, reproduce, forage or hide. 

Some of the species from the deep seem as alien as what we could imagine life to be on another planet. 

  • Barreleye fish 
  • Anglerfish 
  • Dumbo octopus 
  • Lophelia corals 
  • Goblin sharks

Today, the number of deep-sea species identified is estimated to be around 200,000. However, with each new scientific exploration of the deep ocean happening, new species are being identified and named. Considering that we have only explored a little of the ocean, the amount of species living in the deep sea is actually enormous. Some extrapolations suggest that the total number of species found in the deep sea would be around 10 million

Marine life under an unprecedented threat

Although the deep ocean appears so far from us, from our lives and from our eyes, humans are putting a lot of pressure on it. Even the deepest areas of the ocean show signs of human activities. 

In the context of the deep sea, two main human activities are causing the greatest damage: fishing and mining

With the depletion of shallow-waters fish stocks due to intensive fishing, some industrial fishing fleets have directed their efforts to deeper waters to start exploiting previously-untouched fish populations. The main method of fishing is trawling, one of the most destructive ways of extracting fish from the ocean. Deep-sea trawls are big and heavily ballasted fishing nets that scrape the bottom, destroying everything on their way. The impact on deep-sea biodiversity is huge as life grows and develops really slowly at these depths and in these conditions – surely not fast enough to recover before another deep-sea trawl comes. 

At the European level, after many years of campaigning by activists, political leaders, and NGOs such as BLOOM, a new regulation on deep-sea fishing has been put in place to ban bottom trawling below 800 meters and to close some areas from bottom fishing in order to protect vulnerable ecosystems.

More recently, NGOs, scientists and activists have rung the alarm bell over another topic, barely known to the general public: deep-sea mining

The deep sea is full of diverse forms of life but it is also full of metals: iron, manganese, cobalt, nickel, copper... The industrial interest in these resources did not start yesterday, it has been growing for years. An intergovernmental body has even been created in 1994: The International Seabed Authority. Its role is to regulate the exploration and the exploitation of the seabed by attributing permits to companies that are interested in these resources. Today, permits have been allowed to explore more than 1.3 million square kilometres on the high seas (outside of national territories). Permits to start mining will probably be attributed in 2023 although some companies have managed to bypass the whole decision-making process and have obtained permits to start exploiting now. 

Why is this such a problem? We know so little about the deep-sea ecosystems and life down there that it is really hard to know what the impacts of mining could be. However, it has been suggested that mining the depths of the ocean will have devastating effects on deep-sea life due to their fragility and slow recovery

The force of the collective

What can we do in the face of such a situation where the power really seems out of our hands, with decisions being taken behind closed doors and ignoring scientific recommendations? 

At the individual level, it does seem impossible and overwhelming. But as individuals gather together, there is a lot that can be done. Right now, many activists, scientists and NGOs have gathered their forces to put pressure on political leaders. Today, a global movement has started taking place among the civil society and reaching political rooms, asking for a moratorium on deep-sea mining. An alliance of countries calling for a deep-sea mining moratorium has been created, some European parliamentarians have declared supporting the moratorium too and some political leaders such as Emmanuel Macron have expressed their wish to stop mining the high seas during the UN Ocean Conference (Lisbon, earlier this year).

Every day, something new happens regarding the deep-sea mining topic and each day comes with its good and bad news. But there is not a single day without people fighting to get their voices heard – speaking up for life in the deep ocean. The best we can do in this current situation is to stay informed with the latest news and follow NGOs and activists that share petitions and on-the-ground actions to which we can all contribute. 

If you want to learn more about this pressing issue and know how you can act you can follow 

FR @look_down_action @ansroux @grainedepossible @underwaterbaguette @soafrance

EN @diva_amon et  Deep Sea Conservation Coalition (=Save The High Seas) 


The deep ocean really is an extraordinary place, full of wonders to discover and to be amazed by. It is like another part of the universe to be explored – yet on this planet. Instead of wanting to extract and exploit it, we should be observing, exploring and admiring the wonder of what is. If you do also feel like so, let’s try to defend what cannot speak our language, and speak up for them.