The tiny sponge that could help preserve our deep oceans

The Clarion-Clipperton Zone (CCZ) is a vast area of the Pacific Ocean between Mexico and Hawaii. At six million square kilometres, it is roughly 24 times bigger than the UK.

The zone is important because it's the world's largest area of ocean that is targeted for deep-sea mining. Mineral companies and nation states, eager to secure access to precious metals, are attracted to the area because it is rich in polymetallic nodules - small chunks of minerals scattered on the seafloor.

These nodules are mostly made of manganese, but are also rich in cobalt, copper and nickel, which mean they could be a vital resource in developing new technologies like electric cars.

While the potential to harvest the nodules has been recognised since the 1960s, new technologies and the changing price of metals mean that mining is now much closer to being economically viable.

A number of countries have signed exploration contracts for various parts of the CCZ. They are currently restricted to exploration only, but mining exploitation contracts could be signed in the near future.

Some protected areas were designated around those parts of the ocean that have been selected for mining. These Areas of Particular Environmental Interest (APEIs) were chosen to help protect the entire region from the impacts of mining, which are a major environmental risk.

However, it has proved challenging to collect data from them - for example the types of species that live in them and how connected they are to the mining zones. So scientists are still not sure exactly how effective these areas will be.

Scientific data to help seafloor conservation

Scientists at the Museum are studying whether or not these protected areas are useful to conserve the diversity of animals in the deep Pacific Ocean.

In their latest study published in the journal Molecular Ecology, they examined how a small sponge called Plenaster craigi is distributed around the area. The team suggest that although the APEIs do fulfil a useful conservation role, some of these areas might need to be rethought.

Sergi Taboada, a postdoctoral researcher who worked on the study, says, 'This is a unique piece of research that has been many years in the making. Studies like this, with so many deep-sea specimens all analysed genetically at once, are very rare.

'The deep sea is the largest habitat on the planet, yet little is known about it. We need to know much more before choosing which areas should be protected.'

Adrian Glover, principal investigator of the Museum's deep-sea systematics and ecology research group, adds, 'This is the first piece of hard evidence, based on species connectivity data and oceanographic modelling combined, that could be used to help revise the regional environmental management plan of the CCZ.'

Thomas Dahlgren, a co-author and population geneticist at the University of Gothenburg in Sweden, added, 'Plenaster craigi might be a useful canary in the coal mine to assess the impacts of mining once it starts. It is an easily recognisable filter-feeding animal that sits on the nodules and could be impacted by any plumes of sediment from mining machines.'

Detailed study

The CCZ averages between 4,000 and 5,000 metres in depth. It is cold and dark, and food arriving on the seabed is limited to a low rain of particles from the sunlit upper ocean. At that depth, growth is slow and animals are few and far between.

In this study, the team examined the sponge Plenaster craigi, which was described as belonging to a new genus last year by Museum scientists in collaboration with the National University of Singapore and University of Gothenburg.

It lives exclusively on the polymetallic nodules themselves. Although the sponges are miniscule (less than a centimetre long), the description published in 2017 showed they are one of the most common species in the CCZ.

Sergi says, 'This sponge species is interesting because it is sessile and only lives on the nodules. So if all the nodules in one area were mined, those sponges would be heavily impacted.'

Sergi and the team used a detailed DNA method using microsatellites to study the molecular make-up of several sponge specimens from three different areas of the CCZ. One area was the UK-1 area, where the UK has a contract. Another was OMS-1, which is contracted by Singapore, and the last area was a protected Area of Particular Environmental Interest.

The goal was to see whether sponges from the protected area would be able to repopulate the mined areas.

They found that the sponge populations in the UK-1 area and the protected area were connected, but the sponges living in OMS-1 had a very different molecular make-up to the others.

Another part of the study modelled oceanographic currents to look at how the larvae of the sponges might move about.

The results showed a general northerly direction of currents, which fits with the OMS-1 site having a different genetic pattern to the others.

Taken together, the results suggest that although the connectivity between the protected areas and UK-1 is encouraging, increasing the protected areas to the south of the OMS-1 region may have a useful conservation benefit.

Sergi says, 'Examining the gene flow of a species is really important when you are trying to design a protected area.

'Of course, in this study we only examined one species of sponge, and this work should be viewed in a wider context. It would be great to look at how other animals are moving around the area as well, perhaps polychaete worms or isopod crustaceans.

'However, our results do suggest that the protected areas should continue to be revised, and perhaps added to, before any mining begins.'