Megafaunal Ecology of the Western Clarion Clipperton Zone

Abstract

The Clarion Clipperton Zone (CCZ) is a vast area of the central Pacific Ocean where the abyssal seabed is a focus for future polymetallic nodule mining. Broad-scale environmental gradients occur east-to-west across the CCZ seabed, including organic matter supply and nodule abundance, factors that influence benthic faunal community structure and function. A network of protected areas across the CCZ, called Areas of Particular Environmental Interest (APEIs), has been designated to cover this variation. Most previous studies of the benthic environment and megafaunal communities have focussed on the eastern CCZ, leaving the impact of these large-scale gradients unexamined and the network design untested. Seamounts are a further source of heterogeneity in the region. We examined the benthic megafaunal ecology of three APEIs in the western CCZ, spanning a range of environmental conditions. We used a combination of seabed photography and direct sampling to assess the environment and megafauna on the soft sediment habitats on the abyssal plain in three APEIs, and seamounts in two of those APEIs. We found that environmental conditions on abyssal plains differed between the three APEIs in terms of water depth, nodule abundance and coverage, sediment particle size distribution, and estimated organic matter flux. Megafauna were low density and high diversity, with few common morphotypes between sites and many morphotypes being observed only once. Xenophyophores dominated the assemblages. The density and diversity of invertebrates were greater at the sites with lower organic matter inputs and greater nodule abundance. Seamounts in the same APEIs were nodule-free and had coarser sediments than on the plain. Invertebrate megafaunal diversity was lower on the seamounts than on the plains, and most morphotypes recorded on the seamounts were only found on seamounts. Low morphotype overlap also suggests little connectivity between APEIs, and between seamounts and adjacent abyssal plains. Our results provide the first evaluation of the seabed habitats and megafaunal ecology in the western CCZ, highlighting environmental gradients that influence benthic communities, and are important for evaluating the design of the network of protected areas.

Investigating the benthic megafauna in the eastern Clarion Clipperton Fracture Zone (north-east Pacific) based on distribution models predicted with random forest

“…in the north-eastern Atlantic 38 ). However, in accordance with Cuvelier et al 17 , our study shows that seamounts in the German contract area do harbour a distinctly different community compared to nodule field areas nearby (both hills and plains) and, hence, they do not appear to be a suitable refuge for the megabenthic biodiversity found in deeper, nodule-bearing areas, as has been observed in other areas of the CCZ 39 , 40 . Still, it has to be considered that all images used in this study were obtained at abyssal hills and the lower flanks of seamounts and therefore an additional megafaunal assemblage might occur at seamount summits.…”

Benthic megafauna of the western Clarion-Clipperton Zone, Pacific Ocean

“…We provide morphological descriptions, genetic data, and high-resolution imagery for all megafauna specimens collected, including specimens from both the abyssal plains and seamount habitats. It complements similar studies of the high diversity of megafaunal xenophyophores (Gooday et al 2020a, b), and imagery-based community analysis of the megafauna in this area (Durden et al 2021).…”

“…Differences between abyssal plains and seamounts in APEIs 4 and 7 (with only 16 and 19% overlap in Operational Taxonomic Units; OTUs) have been observed from environmental-DNA sampling of sediments, with most OTUs being rare and limited to small areas (Laroche et al 2020). Similarly, image-based surveys in the western APEIs observed very few common morphotypes shared across habitats, with several rare morphotypes observed only once (Durden et al 2021). In addition, Leitner et al (2021) have argued that even if some species are shared between seamounts and the abyssal seafloor, the areal coverage of seamounts is a tiny proportion compared to the areal of abyssal seafloor in the CCZ, so seamounts could supply only a very limited number of propagules for recolonisation over ecological time scales.…”

Benthic megafauna habitats, community structure and environmental drivers at Rio Grande Rise (SW Atlantic)

“…Likewise, Morgan et al (2015) found evidence of changeover in diversity and community structure within cobalt-rich crusts areas and Schlacher et al (2014) suggested the cover of cobalt-rich deposits may drive the structure of benthic communities. Polymetallic nodules in the Clarion-Clipperton Zone (CCZ) are also a potential driver for megafaunal community structure (Cuvelier et al, 2020;Durden et al, 2021;Simon-Lledó et al, 2020). Nevertheless, the exact relationship between the fauna and the chemical nature of the crusts and nodules remains to be further investigated.…”