NEOICHNOLOGY WITH ROVs: DEEP-SEA FISH TRACES AND SEDIMENT RE-SUSPENSION IN THE EASTERN MEDITERRANEAN

Observations by two remotely-operated vehicles (ROVs) at four sites along the bathyal region (500-2,000 m) offshore Israel revealed multiple traces produced by benthic and bentho-pelagic fish that reflect near-bottom activity in one of the most biologically impoverished regions of the World Ocean. High-resolution video and screen captures from the main tethered ROV Hercules were complemented by Argus photography from 15 m above the seafloor to provide a broad view of medium-scale (10-20 cm) biogenic structures. Piscine traces made in soft or partially compacted muddy sediments include grooves, circular and semi-circular depressions, swimming and lateral sliding trails, as well as “resting” traces reflecting sheltering, nesting, and camouflaging/ambush behavior by scorpionfish, rays, eels, flounder, blennoid species, and others. In most cases, the tracemakers were observed in the process of producing the biogenic structures or using burrows and depressions made by other fish and invertebrates. Several types of the imaged traces and seafloor disturbances are known from the rock record (Undichnia and Piscichnus ichnogenera). Their preservation depends on sedimentation rates and overprint by subsequent bioturbation. Near-bottom video also captured various behaviors leading to sediment re-suspension by fish, both through near-bottom contact by pectoral, pelvic, anal, and caudal fins, and by rapid collision with the seafloor. The latter may have been due to ROV approach, but the behavior could be considered analogous to predator avoidance or search for epifaunal or infaunal prey. A similar behavioral response was observed in several species of deep-water squid. Large (1-2 m long) grooves of deep-diving cetaceans (e.g., Cuvier’s beaked whales) were absent from all sites, but were observed in the vicinity of underwater volcanoes in the northern Mediterranean during other legs of this expedition and by earlier researchers. The present study demonstrates that abundant fish traces and sediment re-suspension events represent important processes in the bathyal eastern Mediterranean, shedding new light on benthic species abundance and diversity, constraining the residence time of sediments and nutrients, and offering analogs for biogenic structures and trace fossil assemblages in deep-water shales.