Deep sea mining

Heightened interest in the exploitation of deep seafloor minerals is raising questions on the consequences for the resident fauna. Assessing species ranges and determination of processes underlying current species distributions are prerequisites to conservation planning and predicting faunal responses to changing environmental conditions. The abyssal central Pacific nodule belt, located between the Clarion and Clipperton Fracture Zones (CCZ), is an area prospected for mining of polymetallic nodules.

Recently the CCZ has seen a lot of prospectors and scientists exploring the extend of manganese nodule rock formations that lay amid the sea floor’s sediment. These were discovered as far back as the 1870s during the British Challenger Expedition and but only at the beginning of the 1960s researchers began scientific exploration. 

They nodules look like many black rocks, but they are deposits formed millions of years ago. Rich in metals, including nickel, copper, cobalt and rare earth elements. These minerals became crucial materials necessary for the production of cell phones, computers, and construction materials. It is expected that the mining operations will begin in the next 10-20 years and as per usual nothing is known about its impact on the local fauna. After all nodules are not just simply removed but large amounts of sediment will be displaced and the mechanical extraction represents a considerable impact on these usually very small patches of fauna. 

Mining will affect large areas of the seafloor owing to direct mining disturbance (estimated scales of 300–600 km2 per year) and re-deposition from sediment plumes (over scales of 10–100 km from the mining site), which calls for a systematic conservation planning process and associated establishment of a marine protected area network and adjacent buffer zones across the CCZ.

What's urgently needed is a baseline to get a better understanding of the biodiversity of the affected regions. This is not an easy task as we are looking at water depths of up to 5000 m. Our understanding of the deep sea fauna is patchy at best. Expeditions are costly and the catches are usually very limited in abundance. This does not necessarily mean that live down there is sparse, it is just much harder to find it.

A group of German researchers and one French scientist just published a study in which they assessed macrofaunal distribution patterns in these polymetallic nodule fields. They used DNA Barcoding to examine variations in genetic diversity and connectivity of isopods and polychaetes across the region. 

Specimens were collected from two mining claims (the eastern German and French license areas) located 1300 km apart and influenced by different productivity regimes.  The expeditions brought back 1900 specimens that could be subjected to genetic analysis. With 44% for the polychaetes and 31% for the isopods the success rates were rather low but it seems that the authors only attempted COI amplification with standard Folmer primers which do not work well for both taxonomic groups. Despite this relatively low sequencing success, this study is very comprehensive compared to others investigating species distribution in such regions, and the results are remarkable:

Molecular analyses indicated high local and regional diversity mostly because of large numbers of singletons in the samples. Consequently, variation in composition of genotypic clusters between sites was exceedingly large partly due to paucity of deep-sea sampling and faunal patchiness. A higher proportion of wide-ranging species in polychaetes was contrasted with mostly restricted distributions in isopods. Remarkably, several cryptic lineages appeared to be sympatric and occurred in taxa with putatively good dispersal abilities, whereas some brooding lineages revealed broad distributions across the CCZ. 

This new mineral rush - if not properly controlled - would have a devastating effect on these often unique ecosystems we don't even fully understand. As usual it is easier and cheaper to just go ahead and extract more resources from planet Earth rather than investing more into research that looks at renewable and recyclable solutions to an ever increasing demand. The good news is that the International Seabed Authority requires every contractor to report on environmental status, current biodiversity of the area as well as population structure and standing stocks. The problem is that we know so little and that seriously hampers any such assessment. This study is certainly a step forward in the right direction but once again one done by researchers.

This study represents only a first step towards understanding diversity of two macrobenthic groups in the CCZ and there are furthermore few comparable data to measure our findings against. However, the high genetic diversity, especially the high proportion of cryptic species even in good dispersers and at very small spatial scales, leads to the assumption that the central Pacific might indeed be listed amongst the World’s most diverse deep-sea ecosystems.