Bioturbation and faunal-mediated ecosystem functioning in a deep-sea benthic community recovering from a severe seabed disturbance

Abstract

Kaikōura Canyon, offshore Aotearoa/New Zealand, is a hotspot for deep-sea benthic biology with globally high faunal abundance. The Mw7.8 Kaikōura earthquake in 2016 triggered a severe disturbance that reshaped the canyon, evacuating an estimated 850 metric megatonnes of sedimentary material down canyon. The Kaikōura Canyon habitat is now recovering from this removal of both seafloor substrate and associated organisms.We measured post-event benthic macrofauna density together with biomass and sediment properties and related these to infaunal bioturbation activity, sediment community oxygen consumption (SCOC) and associated benthic macronutrient biogeochemical fluxes. Three legacy sites were used as reference along a depth transect of the canyon axis at 917, 1249, and 1480 m water depths. We found distinct differences in benthic functioning between sites.While many parameters measured followed the expected relationships of decreasing with depth some benthic biological activity metrics did not. Our data suggests that the sites differ based on the relative impact and type of disturbance experienced during the earthquake-triggered, canyon-flushing event. We find SCOC was linked to bioturbatory behaviour and sediment organic matter content, rather than taxa density or biomass. While the greatest bioturbation activity was measured at the shallowest site, the greatest SCOC was measured at the middle depth site due to elevated sediment organic matter content.These observations provide a wider benchmark for infaunal bioturbation and faunal-mediated biogeochemical processes in deep-sea canyon environments and provide rare insights of recovery trajectories for deep-sea benthic communities and ecosystem function after large seafloor disturbances.