Faunal assemblage changes, bioturbation and benthic storms at an abyssal station in the northeastern Pacific

This study investigates the evolution of deep-sea lebensspuren assemblages before, during, and after five high-energy episodes over a storm-events period lasting 25 days. Bioturbational changes were characterized through brief benthic storm events in the northeastern Pacific at the abyssal time-series site Station M (4000 m depth). Quantification of seafloor coverage was processed to evaluate variations on the substratum type. A total of 15 lebensspuren morphotypes were identified. Most traces could be associated with feeding faecal casts, crawling tracks, dwellings and resting structures. Lebensspuren assemblages were similar before and after the storm-events period; full assemblage was re-established in one week. This high energy period was associated with an impoverishment of lebensspuren abundance and assemblage diversity. Only elpidiid holothurian feeding faecal casts recorded a notable increase in abundance during this period of high energy. In addition, this energetic stage involved the appearance of exhumed surface patches. Holothurian feeding activity appeared to have been primarily influenced by the local-scale erosion and re-suspension of unconsolidated surface sediment, which led to the reorganization of organic matter resources. We propose the mobility of elpidiid holothurians allowed them to gain a competitive advantage in obtaining these new resources. This research presents a novel relationship between lebensspuren, faunal activity, and bottom currents that broadens our understanding of benthic community responses to deep-sea bottom currents. Finally, we discuss these results as they pertain to the fossil record to assess how bioturbational structure development could be controlled by substratum type, organic matter availability and duration of energetic episodes.