Results from an in situ experiment at the deep-sea observatory HAUSGARTEN

To study the response of the smaller benthic biota to larger food-falls and their possible effects on the biodiversity at the deep seafloor, we deployed the halves of a sagittally bisected porpoise (1.3 m in length; each half approximately 18 kg) at 2500 m and 5400 m water depth at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the eastern Fram Strait. The sampling of sediments beneath the carcass halves and at different distances (0, 20, 40 cm) from these artificial food-falls was carried out by means of push-corers handled by a Remotely Operated Vehicle five weeks after the food deployment. The samples provided empirical evidence for a quick response by sediment-inhabiting bacteria and metazoan meiofauna to the carcasses at both water depths. Compared to control sediments, the substantial pulse of organic matter also led to generally increased meiofauna/nematode densities around the artificial food-falls. The comparison of nematode communities in sediments affected by the carcasses with those in background control sediments exhibited shifts in the structural composition and the associated trophic and functional diversity of the nematode fauna. Our results confirmed that the impact of large food-falls on the deep benthic community largely depends on environmental factors (water depth, alternative food sources) as well as the background species composition, i.e., the structure of the prevailing meiofauna/nematode assemblages and the composition of the necrophagous community present in the wider area.