Comparison of rosette-shape traces in abyssal terrains: Environmental and faunal implications

Abstract

Biogenic traces (lebensspuren) result from the activity of benthic organisms on and within the seafloor and are a common feature of deep-sea environments. Rosette-shape traces (RSTs), also referred to as spoke burrows, are a commonly observed and distinctive trace, likely created by echiuran worms during feeding and burrowing. We conduct a quantitative morphometric assessment of RSTs from two contrasting sites at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO; Northeast Atlantic) with similar physico-chemical conditions except for relative sediment compaction, but substantive differences in their megabenthic communities. We quantified RST abundance (numerical density and seafloor cover) and morphological characteristics (spoke number and overlap, spoke length and width, trace area and relative completeness) for 148 individual RSTs observed in some 6800 seafloor photograph (8788 m  2 seafloor area) captured with an autonomous underwater vehicle. We derived two primary results between study sites: (a) individual spoke morphology exhibited no statistically significant differences, while (b) individual trace completeness was significantly different. The consistency in spoke morphometrics reflects our identification of a single RST morphotype, potentially representing a single functional group of echiurans. The difference in trace completeness between sites may have resulted from differences in competition for resource with other megabenthic surface deposit feeders, and not to be directly related to relative sediment compaction. By reference to literature data and observations of similar traces in other deep-sea settings, we further suggest that this connection between trace completeness and resource availability may be more generally applicable in both contemporary ecology and paleoichnology.