Abstract
In the Clarion-Clipperton Zone (CCZ) in the north-eastern Pacific Ocean ca. 30 billion tonnes of polymetallic nodules, rich in metals critical for frontier technologies, lay on the sediment surface over an area of 4 to 5 million square kilometres. For this reason, there is accelerating interest in deep-sea mineral mining in the CCZ. Few data exist concerning marine biodiversity in this enormous region and a solid understanding of baseline biodiversity and ecosystem function are necessary in order to inform effective management strategies, conservation and monitoring in the event that mining goes ahead in the CCZ. In this study, 10 in situ baited-camera experiments were carried out in the BGR (The Federal Institute for Geosciences and Natural Resources, Germany) license area in the eastern CCZ to document the biodiversity of scavengers and their feeding activities. Twelve different bait-attending taxa were identified. The most common of these were macrourid, ophidiid and zoarcid fishes, and dendrobranchiate shrimp. Successional patterns regarding their time of arrival were also observed. The bait consumption rate was measured, and a mean scavenging rate of 878 g d-1 ± 113 (SE, n = 9) was calculated, with the rattail Coryphaenoides spp. responsible for the majority of the bait consumption. Polymetallic nodule size did not significantly affect community structure, diversity or scavenging rates within the BGR license area, but significant differences were found in community structure between the BGR area and other areas of the eastern CCZ (the Ocean Minerals of Singapore and UK1 areas). This study increases our knowledge of deep-sea scavenging communities in an area targeted for deep-sea mining.
Highlights
Increasing demand for metals and rare earth elements for use in electronics and renewable energy infrastructure is accelerating research into deep-sea minerals and their potential for exploitation (Wedding et al, 2015; Miller et al, 2018)
Net primary productivity (NPP) is inversely correlated with sea-surface temperature (SST) and reaches a maximum of 379 ± 26.2 mg C m−2 day−1 around March [data derived from the Vertically Generalised Production Model (VGPM); Behrenfeld and Falkowski, 1997a,b; average value retrieved from the Ocean Productivity website1 for the BGR licence area]
Our results show a relatively high diversity of benthic and demersal scavengers in the BGR licence area of the Clarion-Clipperton Zone (CCZ), in line with other similar experiments performed in adjacent licence areas
Summary
Increasing demand for metals and rare earth elements for use in electronics and renewable energy infrastructure is accelerating research into deep-sea minerals and their potential for exploitation (Wedding et al, 2015; Miller et al, 2018). Benthic and demersal scavengers play an important role in nutrient cycling and energy flow in deep-sea ecosystems, consuming and redistributing organic material. They depend on the episodic transport of organic material from the pelagic zone in the form of dead fishes, squids, jellyfish, and cetacean carcasses as well as more refractory plant material (Britton and Morton, 1994; Jeffreys et al, 2010, 2011; Fleury and Drazen, 2013; Sweetman et al, 2014; Dunlop et al, 2017, 2018). Baited-cameras are an effective way to observe these communities due to scavengers’ propensity for constant swimming whilst they look for food, and their relatively scarce abundance over large areas –with hundreds of fish per km in the CCZ (Leitner et al, 2017)
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