Functional roles of abyssal benthos in sustaining polymetallic nodule fields.

Abstract

Polymetallic nodules form a critical habitat in the abyssal plain ecosystems where they occur, supporting high benthic biodiversity.¹ They form over millions of years in areas of extremely low sediment accumulation rates,^2,3 but it is unclear how the nodules remain on the surface, and hence are available for benthic biota. Here, we use seabed time-lapse photography to explore the potential role of benthic faunal behavior in the maintenance of polymetallic nodules on the seabed surface. We observed several species directly removing sediment from the nodule surface, mainly holothurians and gastropods, and infauna activity causing nodule uplift. Derived estimates of the area covered by animal movements, as a proxy for benthic activity,^4,5 indicated that yearly to decadal timescales are needed to remove sediment from and uplift all nodules within the field of view. If these behaviors significantly counteract nodule burial over the long term, then benthic activity may be a key mechanism in nodule maintenance,^6,7 as hypothesized for over 40 years.⁸ This essential function for the maintenance of abyssal biodiversity in nodule-field seascapes has been largely overlooked, highlighting that substantial gaps in knowledge remain in our understanding of the functioning of nodule-field ecosystems. Improving the assessment of habitat engineers may enhance predictions of ecosystem resilience if commercial mining activities occur. However, this study opens new opportunities for monitoring benthic ecosystem functioning to provide a more holistic understanding of abyssal ecosystem status and dynamics.