Multi-scale variations in invertebrate and fish megafauna in the mid-eastern Clarion Clipperton Zone

Erik Simon-Lledó,Christina Pomee,Akesa Ahokava,Jeffrey C Drazen,Astrid B Leitner,Adrian Flynn,John Parianos,Daniel O.B Jones

doi:10.1016/j.pocean.2020.102405

Abstract

The abyssal seafloor of the Clarion Clipperton Zone (CCZ) in the central Pacific has the largest known deposits of polymetallic nodules and associated benthic faunal communities with high biodiversity. The environmental factors that structure these communities, both at regional and local scales, are not well understood. In this study, seabed image surveys were used to assess distribution patterns in invertebrate and fish megafauna (>1 cm) at multiple scales in relation to key environmental factors: food supply to the seabed varying at the regional scale (hundreds of km), seabed geomorphological variations varying at the broad local scale (tens of km), and seabed nodule cover varying at the fine local scale (tens of meters). We found significant differences in megafaunal density and community composition between all study areas. Variations in faunal density did not appear to match with regional productivity gradients, although faunal density generally decreased with increasing water depth (from E to W). In contrast, geomorphology and particularly nodule cover appeared to exert strong control on local faunal abundance and community composition, but not in species richness. Local variations in faunal density and beta-diversity, particularly those driven by nodule presence (within study areas), were of comparable magnitude to those observed at a regional level (between study areas). However, regional comparisons of megabenthic assemblages showed clear shifts in dominance between taxonomic groups (perceivable even at Phylum levels) across the mid-eastern CCZ seabed, suggesting a higher regional heterogeneity than was previously thought.

Highlights

Global economic interest in deep-sea mining has grown since the discovery of extensive polymetallic nodule fields in the equatorial Pacific during the HMS Challenger expedition (Murray and Renard, 1891)
We explore variations in megabenthic community structure at the large scale between sites and couple this with independent assessments for each contract area performed at the finer scale, to investigate how variations in the presumed food supply regime, seabed geomorphology, and nodule cover may affect the distribution of megafauna in the mid-eastern Clarion Clipperton Zone (CCZ) abyss
This paper presents an assessment of megabenthic faunal distribution in response to multiple environmental factors known to generate habitat variability in abyssal environments

Summary

Introduction

Global economic interest in deep-sea mining has grown since the discovery of extensive polymetallic nodule fields in the equatorial Pacific during the HMS Challenger expedition (Murray and Renard, 1891). Abyssal plain and hill environments of the Clarion Clipperton Zone (CCZ) in the central eastern Pacific harbour the largest known deposits of polymetallic nodules, rich in manganese, copper, nickel, and cobalt (Hein et al, 2020). Nodule fields constitute an unusual mosaic habitat in the deep sea (Simon-Lledó et al, 2019b). The hard substratum provided by nodules combined with the background soft sediment acts to increase habitat complexity (Simon-Lledó et al, 2019b), which is thought to promote the occurrence of some of the most biologically diverse seafloor assemblages in the abyss (Amon et al, 2016; Christodoulou et al, 2020; Gooday et al, 2017; Janssen et al, 2015). The closer proximity of the southern areas of the CCZ to the equatorial Pacific

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