The megafauna community from an abyssal area of interest for mining of polymetallic nodules
De Smet, B.; Simon-Lledó, E.; Mevenkamp, L.; Pape, E.; Pasotti, F.; Jones, D.O.B.; Vanreusel, A. (2021). The megafauna community from an abyssal area of interest for mining of polymetallic nodules. Deep-Sea Res., Part 1, Oceanogr. Res. Pap. 172: 103530. https://dx.doi.org/10.1016/j.dsr.2021.103530
In: Deep-Sea Research, Part I. Oceanographic Research Papers. Elsevier: Oxford. ISSN 0967-0637; e-ISSN 1879-0119
Polymetallic nodules increase habitat heterogeneity in some abyssal benthic ecosystems by providing hard substrate. Besides their important role in structuring ecosystems, polymetallic nodules have high grades of valuable minerals and are a target of likely future exploitation, particularly in the Pacific Clarion-Clipperton Zone (CCZ). Mining activities will remove hard substrate and sediment and cause sediment plumes potentially affecting faunal communities over large areas. Long-lived megafaunal assemblages may be particularly vulnerable but data are lacking on the density, biodiversity and community structure in many areas of the CCZ. This study aims to provide megabenthic community baseline data from two physically similar areas (B6S02 and B4S03) located in the contract area of Global Sea Mineral Resources N.V. (GSR). Seafloor images, obtained by an autonomous underwater vehicle are used to characterise the large areas required for robust evaluation of sparse megafauna. Higher altitude images cover a larger area for the same effort but have reduced resolution compared to images obtained closer to the seafloor, leading to difficulties in detecting and identifying individuals. Our comparison of images obtained at different altitudes shows that images taken above 8m altitude underestimate the megafauna density by almost 50%, so images <8m were used for further analysis. We also used multiobserver agreement analysis to improve the megafaunal annotation consistency, and the quality and robustness of the data in this study. The two GSR areas were significantly different in nodule coverage and megafauna composition and a general positive relationship between nodule coverage and megafauna abundance was observed. Differences in the megafaunal composition were primarily caused by differences in echinoderms (asteroids, echinoids, ophiuroids and holothuroids), representing almost 70% of the megafauna.
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