Spatial and temporal variation in megafaunal biodiversity in natural and impacted abyssal environments

Abstract

Abyssal benthic communities, found between 3000 and 6000m, are heterogeneous across space and time. Polymetallic nodule fields are extensive abyssal habitats that support diverse faunal communities. In these habitats, nodules are an essential source of hard substrate that increases the heterogeneity of the seafloor. The Clarion-Clipperton Fracture Zone in the eastern Pacific hosts large expanses of polymetallic nodules and has been targeted as a region of interest for potential future deep-sea mining. Understanding how communities vary across different spatial and temporal scale is essential for determining the drivers of biodiversity patterns in the CCZ and the likely impacts of large-scale mining activity. We used quantitative seafloor imagery to explore local-scale (<100km) spatial and temporal variability in megafaunal communities in the eastern CCZ and the long-term effects of deep-sea mining. Nodule patches can vary in their nodule size and coverage, which here we refer to as nodule-habitat type. We found that local scale (1-100km) changes in the megafauna were associated with variation in nodule-habitat type, with areas containing small, densely packed nodules supporting higher densities but lower diversity of animals. In addition, areas with greater seabed heterogeneity (i.e. multiple nodule-habitat types in one area) had significantly different community structure and higher species richness. These findings highlight the importance of heterogeneity generated by nodules as drivers of community patterns in the CCZ. Megafaunal diversity and community composition were relatively stable in the short-term (over 4 years) in the eastern CCZ, although there was a slight decrease in densities over time, possibly reflecting changes in the quality of the organic material present in the sediments. In the long-term (over 44 years), there appears to be shifts in community composition, however, we could not link this to any environmental changes that may have occurred. Revisiting a mining disturbance test site 44 years later, revealed persistent reductions in megafaunal density and diversity, particularly among sessile suspension feeders. Community and functional structure remained distinctly different in the mining tracks and these results suggest that recovery may not be possible for megafauna in areas where nodules are removed. These findings considerably extend our understanding of the long-term impacts of mining disturbance in the abyss. Spatial and temporal variability in faunal communities needs to be accounted for in spatial management strategies and biodiversity conservation in this region.

More information

Identifiers

ORCID for Bethany Frances Mawdsley Fleming: orcid.org/0000-0002-6608-2841

ORCID for Jon Copley: orcid.org/0000-0003-3333-4325

Catalogue record

Export record