Lebensspuren of the Bathyal Mid-Atlantic Ridge

The extent of megafaunal bioturbation was characterised at flat sedimented sites on the Mid-Atlantic Ridge (MAR) at 2500 m depth. This study investigated the properties of and spatial variation in surficial bioturbation at the MAR. Lebensspuren assemblages were assessed at four superstations either side of the MAR and in two different surface productivity regimes, north and south of the sub-polar front. High-definition ROV videos from these superstations were used to quantify area and abundance of 58 lebensspuren types. Lebensspuren area was lowest at the SW with 4.12% lebensspuren coverage and the SE & NW had the greatest area coverage of lebensspuren (9.69% for both). All stations except the SW were dominated by epifaunal, particularly track-style, lebensspuren. Infaunal mounds were more significant in the southern superstations, particularly in the SW. In terms of lebensspuren assemblage composition, all superstations were significantly different from one another, which directly corresponded with the composition of lebensspuren-forming epifauna. Lebensspuren assemblages appeared to have been primarily influenced by local-scale environmental variation and were independent of detrital flux. This investigation presented a novel relationship between lebensspuren and faunal density that conflicted with the traditionally held view of inverse proportionality and suggests that, at the MAR, megafaunal reworking was not the only significant control on lebensspuren assemblages.