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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-255
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-255
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Jul 2019

Submitted as: research article | 04 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Alpha and beta diversity patterns of polychaete assemblages across the nodule province of the Clarion-Clipperton Fracture Zone (Equatorial Pacific)

Paulo Bonifácio1, Pedro Martinez-Arbizu2, and Lénaïck Menot1 Paulo Bonifácio et al.
  • 1Ifremer, Centre Bretagne, REM EEP, Laboratoire Environnement Profond, ZI de la Pointe du Diable, CS 10070, F-29280 Plouzané, France
  • 2Senckenberg am Meer, DZMB, F-26382 Wilhelmshaven, Germany

Abstract. In the abyssal Equatorial Pacific Ocean, most of the seafloor of the Clarion-Clipperton Fracture Zone (CCFZ), a 6 million km2 polymetallic nodule province, has been preempted for future mining. In light of the large footprint that mining would leave, and given the diversity and the vulnerability of the abyssal fauna, the International Seabed Authority has implemented a regional management plan that includes the creation of nine areas of particular environmental interest (APEIs) located at the periphery of the CCFZ. The APEIs were defined based on the best – albeit very limited – scientific knowledge for the area. The fauna and habitats in the APEIs are unknown, as are species' ranges and the extent of biodiversity across the CCFZ.

As part of the Joint Programming Initiative Healthy and Productive Seas and Oceans (JPI Oceans) pilot action Ecological aspects of deep-sea mining, the SO239 cruise aimed at improving species inventories, determining species ranges, identifying the drivers of beta diversity patterns and assessing the representativeness of an APEI. Four exploration contract areas and an APEI (APEI#3) were sampled along a gradient of sea-surface primary productivity that spanned a distance of 1440 km in the eastern CCFZ. Between 3 and 8 quantitative box cores (0.25 m2; 0–10 cm) were sampled in each study area, resulting in a large collection of polychaetes that were morphologically and molecularly (COI and 16S genes) analyzed.

A total of 275 polychaete morphotypes were identified. Only one morphotype was shared among all five study areas and 49 % were singletons. The patterns in community structure and composition were mainly attributed to variations in food fluxes at the regional scale and nodule density at the local scale. The four exploration contract areas belong to a mesotrophic province. The distance-decay of similarity among the four areas provides an estimated species turnover of 0.04 species km−1 and an average species range of 25 km. The polychaete assemblage in APEI#3 showed the lowest densities, lowest diversity as well as very low, distant-independent similarity with the other four study areas. Given that APEI#3 is located in an oligotrophic province and separated from the CCFZ by the Clarion Fracture Zone, our results call into question the representativeness and the appropriateness of APEI#3 to meet its purpose of preserving the biodiversity of the CCFZ fauna. Two methods for estimating the total number of polychaete species gave estimates that ranged from 498 to 240 000 species. Both methods are biased by the high frequency of singletons in the dataset, which likely result from under-sampling; our estimates thereby merely reflect our level of uncertainty. The assessment of potential risks and scales of biodiversity loss due to nodule mining thus requires an appropriate inventory of species richness in the CCFZ.

Paulo Bonifácio et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Paulo Bonifácio et al.
Data sets

The polychaete fauna of the Clarion-Clipperton Fracture Zone from boxcore samples during SONNE cruise SO239 P. Bonifácio, L. Neal, E. Omnes, B. François, T. G. Dahlgren, and L. Menot https://doi.pangaea.de/10.1594/PANGAEA.902860

Paulo Bonifácio et al.
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Short summary
We found a positive control of polychaete abundance by food supply at regional scale and an influence of nodule cover on species composition at local scale. High levels of alpha and beta diversity are mainly driven by rare species, leading to regional species pool estimates that may range from 498 to 240 000 species. The high proportion of singletons seems reflect an under-sampling bias which is currently preventing the assessment of potential biodiversity loss due to nodule mining.
We found a positive control of polychaete abundance by food supply at regional scale and an...
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