Unexpected high abyssal ophiuroid diversity in polymetallic nodule fields of the Northeast Pacific Ocean, and implications for conservation

Abstract

<p><strong>Abstract.</strong> The largest and commercially appealing mineral deposits can be found in the abyssal seafloor of the Clarion-Clipperton Zone (CCZ), a polymetallic nodule province, in the NE Pacific Ocean, where experimental mining is due to take place. In anticipation of deep-sea mining impacts, it has become essential to rapidly and accurately assess biodiversity. For this reason, ophiuroid material collected during seven scientific cruises from five exploration license areas within CCZ, one area protected from mining (APEI3, Area of Particular Environmental Interest) in the periphery of CCZ and the DIS-turbance and re-COLonisation (DISCOL) Experimental Area (DEA), in the SE Pacific Ocean, was examined. Specimens were genetically analysed using a fragment of the mitochondrial cytochrome c oxidase subunit I (COI). Maximum Likelihood and Neighbour Joining trees were constructed, while four tree-based and distance-based methods of species delineation (ABGD, BINs, GMYC, mPTP) were employed to propose Secondary Species Hypotheses (SSHs) within the ophiuroids collected. The species delimitations analyses concordant results revealed the presence of 43 deep-sea brittle stars SSHs, revealing an unexpectedly high diversity and showing that the most conspicuous invertebrates in abyssal plains have been so far considerably under-estimated. The number of SSHs found in each area varied from 5 (IFREMER area) to 24 (BGR area), while 13 SSHs were represented by singletons. None of the SSHs was found to be present in all 7 areas, while the majority of species (44.2 %) had a single-area presence (19 SSHs). The most common species were Ophioleucidae sp. (Species 29), <i>Amphioplus daleus</i> (Species 2) and <i>Ophiosphalma glabrum</i> (Species 3), present in all areas except APEI3. The biodiversity patterns could be mainly attributed to POC fluxes that could explain the highest species numbers found in BGR (German contractor area) and UKSRL (UK contractor area) areas. The five exploration contract areas belong to a mesotrophic province, while in contrary the APEI3 is located in an oligotrophic province which could explain the lowest diversity as well as very low similarity with the other six study areas. Based on these results the representativeness and the appropriateness of APEI3 to meet its purpose of preserving the biodiversity of the CCZ fauna are questioned. Finally, this study provides the foundation for biogeographic and functional analyses that will provide insight into the drivers of species diversity and its role in ecosystem function.</p>

Polymetallic nodules are essential for food-web integrity of a prospective deep-seabed mining area in Pacific abyssal plains

“…It is not clear, whether this would affect the mined areas only or would result in regional or even global loss of biodiversity (Van Dover et al, 2017; Niner et al, 2018; Washburn et al, 2019). Ophiuroidea, for instance, have an unexpectedly high biodiversity in the CCZ (Christodoulou et al, 2019, 2020), and further discoveries of faunal biodiversity hubs in the poorly-studied deep sea (Ramírez-Llodrà et al, 2010) can be expected. In fact, we even neglected two very diverse taxonomic kingdoms, i.e., Bacteria and Archaea, in our study because we were not able to incorporate them adequately due to a poor understanding of their metabolic pathways.…”

Comparative reproductive biology of deep-sea ophiuroids inhabiting polymetallic-nodule fields in the Clarion-Clipperton Fracture Zone

“…Responsive reproductive modes of this sort appear to be a feature of bathyal and abyssal ecosystems in the tropical NE Pacific (Kuhnz et al, 2014; Smith et al, 2018) where the influences of episodic disturbance events are of greater influence than seasonal changes in surface productivity. Further sampling could also establish whether apparent downward trends in the proportions of late-stage oocytes found in the female specimen from the oligotrophic APEI 3 (Vanreusel et al, 2016; Christodoulou et al, 2020) reflect a lag in maturation rate, energetic constraints on reproductive output or simply a sampling artefact.…”

“…Ophiomusa lymani in N Atlantic & NE Pacific, Gage, 1982; Gage and Tyler, 1982; Ophiocten hastatum in NE Atlantic, Gage et al, 2004; Ophiura bathybia, Amphilepis patens, Amphiura carchara and O. cosmica in NE Pacific, Booth et al, 2008; Ophiura irrorata loveni, Ophiura lienosa, Amphioplus daleus, O. cosmica, Ophiernus quadrispinus and Ophioplexa condita in S Indian Ocean, Billett et al, 2013), with no data available for specimens originating from polymetallic-nodule habitats. As part of a wider concerted effort to address significant knowledge gaps in our understanding of nodule-rich seabed ecology while this habitat remains relatively pristine, the current study describes the reproductive biology of the brittle stars Ophiosphalma glabrum Lütken & Mortensen, 1899 (Ophiosphalmidae) and Ophiacantha cosmica Lyman, 1878 (Ophiacanthidae), two of the more frequently encountered ophiuroids within the eastern CCZ (Christodoulou et al, 2020), based on histological analyses of specimens collected from several mining-contract areas within the eastern CCZ.…”

Convergent Evolution and Structural Adaptation to the Deep Ocean in the Protein-Folding Chaperonin CCTα

“…2014 , 2017 ) and they represent a major component of the deep-sea fauna in terms of abundance and species diversity ( Christodoulou et al. 2019 ; Christodoulou et al. 2020 ), making them important models for marine biodiversity and biogeography ( Woolley et al.…”