Nematode Community Dynamics in the Arctic Deep Sea in Response to Experimental Alterations in Organic Matter Quantity and Quality

Successional dynamics of deep-sea nematode communities are shaped by environmental conditions, resource availability, and ecological processes such as species interactions, dispersal, and disturbance. This study investigates the in-situ response of free-living nematodes to artificial organic matter enrichment at the deep-sea floor in the Arctic Ocean. The experiment was conducted at 1265 m depth at the LTER HAUSGARTEN observatory in Fram Strait. We created azoic sediments with a grain size composition similar to natural deep-sea sediments and applied three treatments: (1) azoic sediment (control), (2) azoic sediment treated with fresh Phaeocystis , and (3) azoic sediment treated with decaying Phaeocystis . The organic content of the artificial sediments was adjusted to match that of natural sediments. The experimental setup was deployed for three months with a bottom lander and compared to natural sediment samples for reference. Despite similar organic carbon content, artificial sediments exhibited lower nematode abundance and diversity compared to natural sediments, indicating an early successional state dominated by opportunistic taxa. Organic enrichment influenced community composition, with fresh Phaeocystis favouring epistrate feeders and decaying Phaeocystis supporting later-stage colonisers. Natural sediments, characterized by long-term stability and organic accumulation, supported higher nematode abundance, functional diversity, and a balanced trophic structure. These findings indicate that a mature community requires more time to develop than the three-month duration of the experiment. Our findings emphasize the role of organic matter retention and long-term sediment accumulation in shaping deep-sea nematode communities and highlight the potential ecological consequences of anthropogenic-driven changes in organic matter deposition, which could affect deep-sea biodiversity and ecosystem resilience. • Artificial sediments had lower nematode abundance and were dominated by opportunistic genera, indicating early successional stages • Natural sediments supported a mature, diverse nematode community • Sediments enriched with fresh Phaeocystis favoured epistrate-feeding nematodes • Sediments enriched with decayed Phaeocystis favoured later-stage nematode colonisers