Diversity and density relationships between lebensspuren and tracemaking organisms: a study case from abyssal northwest Pacific

In the deep sea, interactions between benthic fauna and seafloor sediment primarily occur through bioturbation that can be preserved as traces (i.e. lebensspuren). Lebensspuren are common features of deep-sea landscapes and are more abundant than the organisms that produce them (i.e. tracemakers), rendering lebensspuren promising proxies for inferring biodiversity. The density and diversity relationships between lebensspuren and benthic fauna remain unclear, and contradicting correlations have been proposed (i.e. negative, positive, or even null correlations). To approach these variable correlations, lebensspuren and benthic fauna were characterized taxonomically at eight deep-sea stations in the Kuril-Kamchatka Trench area, together with two novel categories: tracemakers (specific epibenthic fauna that produce these traces) and degrading fauna (benthic fauna that can erase lebensspuren). No general correlation (overall study area) was observed between diversities of lebensspuren, tracemakers, degrading fauna, and fauna. However, a diversity correlation was observed at specific stations, showing both negative and positive correlations depending on: (1) the number of unknown tracemakers (especially significant for dwelling lebensspuren); (2) the lebensspuren with multiple origins; and (3) tracemakers that can produce different lebensspuren. Lebensspuren and faunal density were not correlated. However, lebensspuren density was either positively or negatively correlated with tracemaker densities, depending on the lebensspuren morphotypes. A positive correlation was observed for resting lebensspuren (e.g. ophiuroid impressions, Actiniaria circular impressions), while negative correlations were observed for locomotion-feeding lebensspuren (e.g. echinoid trails). In conclusion, lebensspuren diversity may be a good proxy for tracemaker biodiversity when the lebensspuren–tracemaker relationship can be reliable characterized. Lebensspuren–density correlations vary depending on the specific lebensspuren residence time, tracemaker density, and associated behaviour (rate of movement). Overall, we suggest that lebensspuren density and diversity correlations should be studied with tracemakers rather than with general benthic fauna. On a global scale, abiotic (e.g. hydrodynamics, substrate consistency) and other biotic factors (e.g. microbial degradation) may also play an important role.</p

Diagnostic criteria using microfacies for calcareous contourites, turbidites and pelagites in the Eocene–Miocene slope succession, southern Cyprus

Interbedded contourites, turbidites and pelagites are commonplace in many deep-water slope environments. However, the distinction between these different facies remains a source of controversy. This detailed study of calcareous contourites and associated deep-marine facies from an Eocene–Miocene sedimentary succession on Cyprus clearly documents the diagnostic value of microfacies in this debate. In particular, the variability of archetypical bi-gradational contourite sequences and their internal subdivision (bedding, layering and lamination) are explored. Contourites can be distinguished from turbidites, pelagites and hemipelagites by means of carbonate microfacies in combination with bed-scale characteristics. Particle composition provides valuable information on sediment provenance. Depositional texture, determined by the ratio between carbonate mud and bioclasts, is crucial for identifying bi-gradational sequences in both muddy and sandy contourites, and normally-graded sequences in turbidite beds. Equally important are the type and preservation of traction structures, as well as the temporality and impact of bioturbation. Shell fragmentation under conditions of increased hydrodynamic agitation (textural inversion) is recognized as a carbonate-specific feature of bioclastic sandy contourites.Spanish Ciencia y Tecnologias Marinas projects CTM 2012-39599C03 CGL2016-80445-R CTM2016-75129-C3-1-RSecretaria de Estado de I+D+I, Spain CGL201566835-P PID2019-104625RB-100PFEDER Andalucía B-RNM-072-UGR18Junta de Andalucía P18-RT-4074Universidad de Granada UCE2016-05Projekt DEAL (University of Greifswald in the Alliance of German Science Organizations