The effects of deep-sea mining are unpredictable

How could deep-sea mining and the extraction of manganese nodules affect the ecosystem?

There is so little knowledge about this ecosystem that we really can't predict what will happen if commercial mining of manganese nodules is allowed in the deep sea. We don't know what impact the mining of manganese nodules will have, but we do know that many species depend on such structures because they are used as habitats. The mining equipment is more or less comparable to a hoover. They are designed to suck up the nodules from the seabed. Together with the nodules, however, the sediments associated with the nodules are also collected. The upper layer of sediment on the seabed is a very special habitat in which thousands of animals live. This layer is acutely threatened by the mining process. In addition, the machines are heavy and the bottom of the deep sea is very fluffy, so that the sediment is compacted and several animals living there could be harmed as a result. Researchers from around the world are currently working to understand the communities in this particular habitat in order to better assess the biodiversity and environmental costs that deep-sea mining will cause.

Could the impact be limited to the local level?

Some models predict that mining will have a localised impact. However, many aspects need to be taken into account. For example, there are very direct impacts such as the removal of nodules and sediments, but there are also other indirect impacts. For example, the removal of the nodules creates a sediment cloud and the water currents transport the sediments to other areas where other animals such as filter feeders are affected. In addition, the ships and pipelines that remove the nodules and sediments cause noise and an increase in water temperature, which can affect plankton communities and fish, among others.

What is currently happening?

It's more complex than we can imagine: For example, areas near the coast are well positioned by law because they belong to a particular country. However, the areas beyond the exclusive economic zones - such as the deep sea - are considered a resource that belongs to all people and it is difficult to reach agreements on how they should be utilised. So far, legislation only allows exploration through licence areas. This means that countries can apply for a licence area, and once they have obtained such an area, they can explore the resources, such as existing minerals or biodiversity, without economic benefit. Currently, several research teams are working together to carry out a biodiversity assessment to get a better picture of how many species live in and depend on this particular ecosystem. With regard to mining, we need to make predictions about how many species would be lost. Another important step, which has already been discussed, would be to establish marine protected areas.

What do we actually know about the deep sea?

We know very little about the deep sea. Some even say that we know more about the moon. About 95 per cent of the knowledge gained from the deep sea is new to science. So we know nothing. There are many species to describe, great diversity in many ways, morphological features that have never been seen before, different functions of the animals and also different habitats to explore. In 2018, we conducted a biodiversity assessment expedition - in a small area of about 300 square metres, and only there, we found more than 400 species of copepods. We were able to analyse all these species using genetic methods such as barcoding, but we also looked at the morphology of the different animals. In fact, of all the animals we analysed, we were only able to identify one species that had already been described; the others are probably completely new species. In this case, we only analysed the copepods, but of course this also applies to many other animal groups. There are areas that have never been explored, so there is still a lot to do in this respect.

How is it that the deep sea has been so little researched?

One reason for this is that exploring the deep sea is very time-consuming and therefore also very expensive. This place is difficult to access: you need very different levels of expertise among the expedition leaders and the researchers who take part in the expeditions. Just getting to some areas can take several days. You also need very specialised equipment to be able to take samples and an experienced team to help you make the most of every expedition.

What is the ecosystem like down there?

As far as the animals living in the sediments are concerned, the first five centimetres show a great diversity of species. We are trying to understand their role in the ecosystem. Nematodes and copepods are the two groups that make up 95 per cent of the meiobenthic communities in the deep sea. They live in the sediment or swim near the sediment. Another interesting feature is that for many invertebrate groups, the species living in the deep-sea sediments are also considered to be the oldest of their groups. So if we want to understand the evolution of a particular group - like copepods - we should include these species in our analysis. If we do this, we can better understand how all the changes have taken place over the course of a group's evolutionary history: Why an animal that lived in the sediment had to take another evolutionary step or evolved into a parasite, for example.

As a scientist at the LIB, how can you help to protect the ecosystem?

In general and in the scientific community, we try to understand and describe the diversity and function of ecosystems and the different animal groups. We want to provide more data so that decision-makers are better informed and hopefully make the right decisions to ensure the conservation of diversity.

Dr Nancy Mercado Salas has been Curator of the Crustacean Collection at the LIB since 1 August 2021. Previously, she worked at Senckenberg am Meer (DZMB) for six years on projects to describe the diversity of crustaceans and their colonisation processes in the meiobenthos. She later worked on analysing the diversity of deep-sea crustaceans living in areas threatened by deep-sea mining, such as the Clarion-Clipperton Fracture Zone.