Short and decadal impacts of seafloor physical perturbation on the abundances of Lebensspuren ‘traces of life’ in the Peru Basin manganese nodule province.

Abstract

Abstract Interest in deep sea mining for polymetallic nodules as an alternative source to onshore mines for various high technology metals has risen in recent years, as demands and costs have increased. The need for studies to assess its short- and long-term consequences on polymetallic nodule ecosystems is therefore also increasingly prescient. Recent image-based expedition studies have described the temporal impacts on epi-/megafauna seafloor communities across these ecosystems at particular points in time. However, these studies have failed to capture information on large infauna within the sediments or give information on potential transient and temporally limited users of these areas, such as mobile surface deposit feeders or fauna responding to bloom events or food fall depositions. This study uses data from the Peru Basin polymetallic nodule province where the seafloor was disturbed in 1989 and 2015 to simulate mining disturbance. To try and address the shortfall on transient fauna and infauna use of these various disturbed and undisturbed regions of nodule-rich seafloor, images collected 6 months after the 2015 disturbance event were inspected and all Lebensspuren, ‘traces of life’ were characterized by type and logged, along with whether they occurred on undisturbed seafloor, or regions disturbed in 1989 or 2015. The results show that traces of surface/ocean interface use of disturbed areas by infauna and mobile fauna are at least 50% lower, even 26 years after disturbance, with many trace categories not present in even low numbers on disturbed seafloor areas.