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

Abstract

<p><strong>Abstract.</strong> In the abyssal Equatorial Pacific Ocean, most of the seafloor of the Clarion-Clipperton Fracture Zone (CCFZ), a 6 million km<sup>2</sup> 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.</p> <p>As part of the Joint Programming Initiative Healthy and Productive Seas and Oceans (JPI Oceans) pilot action <q>Ecological aspects of deep-sea mining</q>, 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 m<sup>2</sup>; 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.</p> <p>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<sup>−1</sup> 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.</p>

Taxonomic assessment of deep-sea decapod crustaceans collected from polymetallic nodule fields of the East Pacific Ocean using an integrative approach

“…Despite the fact that the CCZ is perhaps the most persistently-studied abyssal ecosystem (Glover et al 2018), the high proportion of new species recorded and discovered (i.e. Bonifacio et al 2020;Christodoulou et al 2019Christodoulou et al , 2020Brix et al 2020) underlines the limited information presently available on its biodiversity. Megafauna biodiversity assessments in the CCZ and DEA areas are largely dependent on seafloor image surveys (i.e.…”

Toward a reliable assessment of potential ecological impacts of deep‐sea polymetallic nodule mining on abyssal infauna

“…Polychaetes and crustaceans together can represent up to 79% of the absolute sampled organisms (Hessler and Jumars 1974;Wilson 2017). More than 500 macrofaunal morphospecies, including polychaetes, isopods, tanaidaceans, and ophiuroids have been documented in different studies of the CCFZ (Paterson et al 1998;Glover et al 2002;Wilson 2017;Bonif acio et al 2019;Janssen et al 2019Janssen et al , 2015Błażewicz et al 2019b;Christodoulou et al 2020), but very few have been formally described (Riehl et al 2014;Paterson et al 2016;Bonifacio and Menot 2019;Jakiel et al 2019;Wiklund et al 2019;Chim and Tong 2020;Riehl and De Smet 2020).…”

“…The structure and composition of polychaete and tanaidacean assemblages reported for the eastern CCFZ is mostly controlled by organic carbon fluxes to the seafloor (Bonifácio et al 2019; Błażewicz et al 2019 b ). Investigating benthic communities of both western and eastern CCFZ, Wilson (2017) found contrasting productivity‐diversity relationships for polychaetes, tanaidaceans, and isopods.…”

“…While both polychaetes and tanaidaceans showed highest diversity at the highest productivity site, this trend was reversed for Isopoda (Wilson 2017). At the local scale, nodule density also influences the composition of polychaete assemblages (Bonifácio et al 2019) and was reported to have either a positive (Yu et al 2018) or no (Pasotti et al 2020) influence on macrofaunal densities.…”