Biological effects 26 years after simulated deep-sea mining

Erik Simon-Lledó,Daniel O B Jones,Kevin Köser,Veerle A I Huvenne,Brian J Bett,Timm Schoening,Jens Greinert

doi:10.1038/s41598-019-44492-w

Abstract

The potential for imminent abyssal polymetallic nodule exploitation has raised considerable scientific attention. The interface between the targeted nodule resource and sediment in this unusual mosaic habitat promotes the development of some of the most biologically diverse communities in the abyss. However, the ecology of these remote ecosystems is still poorly understood, so it is unclear to what extent and timescale these ecosystems will be affected by, and could recover from, mining disturbance. Using data inferred from seafloor photo-mosaics, we show that the effects of simulated mining impacts, induced during the “DISturbance and reCOLonization experiment” (DISCOL) conducted in 1989, were still evident in the megabenthos of the Peru Basin after 26 years. Suspension-feeder presence remained significantly reduced in disturbed areas, while deposit-feeders showed no diminished presence in disturbed areas, for the first time since the experiment began. Nevertheless, we found significantly lower heterogeneity diversity in disturbed areas and markedly distinct faunal compositions along different disturbance levels. If the results of this experiment at DISCOL can be extrapolated to the Clarion-Clipperton Zone, the impacts of polymetallic nodule mining there may be greater than expected, and could potentially lead to an irreversible loss of some ecosystem functions, especially in directly disturbed areas.

Highlights

In addition to the likely direct mortality of benthic fauna along mining machine tracks, nodule removal will alter the character of the seafloor habitat for the very long-term[15]
Among the six dominant taxonomic groups selected for individual assessment (Fig. 2a–f), only the Holothuroidea exhibited no significant variation in density between disturbance levels (F[3,21] = 1.81, p = 0.1771); the other five taxa groups assessed (i.e. Anthozoa, Porifera, Crustacea, Ophiuroidea, Fish) exhibited statistically significant density variations (F[3, 21] ≥ 9.93, p < 0.0005) of substantial magnitude (η2 ≥ 0.57; Table 1) across the different seabed disturbance levels surveyed
Fish density was enhanced at intermediate disturbance levels, while Ophiuroidea density described a step-up change from reference area (REF) to DISCOL Experimental Area (DEA) (Fig. 3d)

Summary

Introduction

In addition to the likely direct mortality of benthic fauna along mining machine tracks, nodule removal will alter the character of the seafloor habitat for the very long-term (i.e. thousands of years)[15]. An 8 m-wide plough-harrow was towed 78 times through the centre of a study area (~1100 ha), the DISCOL Experimental Area (DEA), to simulate some of the impacts expected from the use of a nodule collector vehicle[14,21]. Metazoan megafauna numerical density and total taxon richness were dramatically reduced in the ploughed areas of the DEA immediately after disturbance and remained substantially reduced 7-years later; the effects being most marked in the case of nodule-attached fauna[24]. We revisited the DISCOL site 26 years after the mining simulation experiment to investigate whether past disturbance still influences the distribution of megabenthic faunal assemblages within this area. We assessed the temporal and spatial responses to disturbance of dominant megafauna groups, as well as community diversity These results are used to understand better the context and scale of potential commercial mining disturbance

Methods

Results

Conclusion