Abundant and diverse ecosystem found in area targeted for deep-sea mining

A sea cucumber on a bed of polymetallic nodules. Credit: Amon and Smith, UHM.

A cnidarian attached to a dead sponge stalk on a nodule. Credit: Amon and Smith, UHM.

A fish and brittle star in a field of polymetallic nodules. Credit: Amon and Smith, UHM.

In a study published in Scientific Reports, scientists discovered impressive abundance and diversity among the creatures living on the seafloor in the Clarion-Clipperton Zone (CCZ) — an area in the equatorial Pacific Ocean being targeted for deep-sea mining. The study, lead authored by Diva Amon, a post-doctoral researcher at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST), found that more than half of the species they collected were new to science, reiterating how little is known about life on the seafloor in this region. 

“We found that this exploration claim area harbors one of the most diverse communities of megafauna [animals over 2 cm in size] to be recorded at abyssal depths in the deep sea,” said Amon.

The deep sea is where the next frontier of mining will take place. A combination of biological, chemical and geological processes has led to the formation of high concentrations of polymetallic “manganese” nodules on the deep seafloor in the CCZ — an area nearly the size of the contiguous United States. These nodules are potentially valuable sources of copper, nickel, cobalt and manganese, among other metals, which has led to an interest in mining this region. All of the potential polymetallic-nodule exploration contracts that have been granted in the Pacific are in this region, according to the International Seabed Authority.

This study, part of the ABYSSLINE Project, was the first to characterize the abundance and diversity of seafloor-dwelling animals, a key component of deep-sea ecosystems, in an exploration claim area leased to UK Seabed Resources Ltd (UK-1) in the eastern portion of the CCZ.

Using a remotely operated vehicle, the research team surveyed the seafloor at four sites within the UK-1 exploration contract area and at a site east of the UK-1 area to estimate abundance and diversity of the ecosystems. 

The preliminary data from these surveys showed that more animals live on the seafloor in areas with higher nodule abundance. Further, the majority of the megafaunal diversity also appears to be dependent on the polymetallic nodules themselves, and thus are likely to be negatively affected by mining impacts.

“The biggest surprises of this study were the high diversity, the large numbers of new species and the fact that more than half of the species seen rely on the nodules — the very part of the habitat that will be removed during the mining process,” said Amon.

Exploitation plans are pushing ahead even though knowledge of the seafloor ecosystem in this region is still limited.

“In order to more effectively manage the area and mitigate the environmental impacts of deep-sea mining in the CCZ and within the UK-1 contract area, baseline knowledge of the abundance, diversity, and species ranges of megafauna — a key component of this ecosystem — is essential,” said Craig Smith, oceanography professor at UHM SOEST and ABYSSLINE lead investigator. 

The ABYSSLINE team will be publishing many more papers about the seafloor biology of the CCZ, with forthcoming papers from UHM scientists including an atlas of megafauna from the UK-1 exploration contract area, a study documenting extremely high diversity in the community of macrofaunal community (crustaceans, worms, mollusks and other invertebrates between 2 and 0.3 cm in size) in the UK-1 exploration claim area.

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This is part of the ABYSSLINE Project, an international program led by Craig Smith at UHM with investigators from six countries, which is conducting benthic biological baseline surveys for the UK Seabed Resources Ltd. exploration contract area (UK-1) in the CCZ in accordance with the ISA stipulation that prior to exploitation, a benthic biological baseline study must be undertaken for each exploration contract area. This work was funded by UK Seabed Resources Ltd. and the University of Hawai‘i at Mānoa.

Diva J. Amon, Amanda F. Ziegler, Thomas G. Dahlgren, Adrian G. Glover, Aurélie Goineau, Andrew J. Gooday, Helena Wiklund & Craig R. Smith (2015) Insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone. Scientific Reports, DOI: 10.1038/srep30492.

Full photo captions:

Amperima sp.:
An Amperima holothurian or sea cucumber seen on a bed of polymetallic nodules in the eastern Clarion-Clipperton Zone. Several corals, a sponge and a brittle star can also be seen in the image. Photo credit: Diva Amon and Craig Smith, University of Hawai‘i at Mānoa.

Relicanthus sp.:
A species of cnidarian in the genus Relicanthus with 8-foot long tentacles attached to a dead sponge stalk on a nodule in the eastern Clarion-Clipperton Zone. These are closely related to anemones. Photo credit: Diva Amon and Craig Smith, University of Hawai‘i at Mānoa.

Bathysaurus mollis:
The fish Bathysaurus mollis and brittle star seen in a field of polymetallic nodules in the eastern Clarion-Clipperton Zone. Photo credit: Diva Amon and Craig Smith, University of Hawai‘i at Mānoa.