Environmental Heterogeneity Throughout the Clarion-Clipperton Zone and the Potential Representativity of the APEI Network

Abstract

Environmental variables such as food supply, nodule abundance, sediment characteristics, and water chemistry may influence abyssal seafloor communities and ecosystem functions at scales from meters to thousands of kilometers. Thus, knowledge of environmental variables is necessary to understand drivers of organismal distributions and community structure, and for selection of proxies for regional variations in community structure, biodiversity, and ecosystem functions. In October 2019, the Deep CCZ Biodiversity Synthesis Workshop was conducted to (i) compile recent seafloor ecosystem data from the Clarion-Clipperton Zone (CCZ), (ii) synthesize patterns of seafloor biodiversity, ecosystem functions, and potential environmental drivers across the CCZ, and (iii) assess the representativity of no-mining areas (Areas of Particular Environmental Interest, APEIs) for subregions and areas in the CCZ targeted for polymetallic nodule mining. Here we provide a compilation and summary of water column and seafloor environmental data throughout the CCZ used in the Synthesis Workshop and in many of the papers in this special volume. Bottom-water variables were relatively homogenous throughout the region while nodule abundance, sediment characteristics, seafloor topography, and particulate organic carbon flux varied across CCZ subregions and between some individual subregions and their corresponding APEIs. This suggests that additional APEIs may be needed to protect the full range of habitats and biodiversity within the CCZ.

Bacterial and Archaeal Communities in Polymetallic Nodules, Sediments, and Bottom Waters of the Abyssal Clarion-Clipperton Zone: Emerging Patterns and Future Monitoring Considerations

“…The bottom waters showed less spatial separation, with weak partitioning along the east-west divide (Figure 2B), while nodules appeared to vary more by cruise than by geographic location as such (Figure 2D). These biogeographic patterns are consistent with the broad patterns seen in physicochemical variables across the CCZ: bottom waters are similar across the region, while multiple parameters expected to affect benthic organisms (e.g., modeled particulate organic carbon flux to the seafloor, water depth, and sediment composition) vary both from the eastern to western CCZ and latitudinally within the western CCZ (Washburn et al, 2021).…”

“…Because the energy used by abyssal microbes at sites such as the CCZ that are distant from hydrothermal features ultimately derives from inputs from the surface ocean, the biogeochemical gradients in the upper water column of the south-eastern Pacific raise the possibility of similar, related habitat gradients at the seafloor. These biogeochemical gradients include particulate organic carbon flux to the sediments, which decreases northward from the equatorial upwelling region into the stratified gyre proper, as well as from east to west (Christian et al, 2002;McQuaid et al, 2020;Washburn et al, 2021). East-west variability in particulate organic carbon flux has been posited to explain spatial patterns in species richness of nodule-associated xenophyophores and metazoans (Veillette et al, 2007).…”

Biogeography and Connectivity Across Habitat Types and Geographical Scales in Pacific Abyssal Scavenging Amphipods

“…For this site, very low abundances of predators, with an overall maximum of 3 individuals of a single predator species observed in either of the two baited camera deployments, were reported (Leitner et al, 2021). The high diversity could be driven by the low abundance of predators, but could also be driven by the seamount higher habitat heterogeneity (Washburn et al, 2021a) or by its oligotrophic condition (McQuaid et al, 2020). Oligotrophy has been associated with lower abundances but higher species diversity of scavenging amphipods compared to eutrophic sites (Horton et al, 2020c), and higher habitat heterogeneity has been also linked to higher diversity.…”

Testing the Seamount Refuge Hypothesis for Predators and Scavengers in the Western Clarion-Clipperton Zone

“…While highly mobile animals are often found in a variety of habitats, their core habitat, where they are naturally the most abundant, is often needed to sustain reproductive populations (Drazen et al, 2019). Moreover, seamounts make up only 0.3% of the habitat area of the CCZ (Washburn et al, 2021) and ecological research shows that a 99% (Gehlenborg, 2019).…”