DIVERSE ICHNOFAUNA OF BATHYAL (500-2,000 M) SOFTGROUNDS: DUAL ROV OBSERVATIONS OFFSHORE ISRAEL

A diverse suite of vertebrate and invertebrate traces was documented by a tandem of tethered remotely-operated vehicles (ROVs) in the bathyal region of the eastern Mediterranean Sea. Hours of high-resolution digital video and more than 3,000 screen captures from ROV Hercules were used to locate, identify, and measure traces produced by benthic biota in one of the world’s most oligotrophic marine regions. The aerial distribution of medium-to-large (>10 cm) traces associated with submarine canyons, regions of mass-wasting, and high-sedimentation basins was assessed with video and photography from ROV Argus. The trace-making organisms include adult and juvenile species of fish, cephalopods, gastropods, arthropods, crustaceans, echinoids, holothurians, sessile coelenterates, as well as abundant echiurans and several worm genera. Many tracemakers were observed in the process of producing the structures – a crucial aspect of neoichnological research. In addition to burrow complexes and intricate 1-3-cm-wide graphoglyptid trails typical of Zoophycos and Nereites ichnofacies, biogenic structures include simple feeding, dwelling, and locomotion traces common for outer shelf mud-dominated softgrounds (Cruziana ichnofacies) and isolated stiff/firmground assemblages (Glossifungites). The definition and preservation of these features is a function of their original size, relief (scour depth and elevation of marginal ridges), net sedimentation rate, and age. Some traces may be obliterated, overprinted, or re-excavated by the trace-maker or other species (e.g., dense bioturbation of abandoned structures, use of crustacean burrow complexes by eels for sheltering and feeding, localized re-suspension of the upper sediment layer by fish and squid). Controlled laboratory experiments aimed at reproducing such structures are logistically challenging or impossible due to unique physical or biological requirements. Therefore, deep-sea technology presents exceptional opportunities by not only revealing the traces, but also capturing the identity and behavior of trace-making organisms. In-situ observations and image analysis aid biologists in compiling the census of biota in largely inaccessible parts of the ocean and offer geoscientists important insights into ancient deep-sea ichnocoenoses.