Feeding Characteristics of Deep-Sea Acorn Worm (Hemichordata, Enteropneusta, Torquaratoridae) from the Bering Sea

Deep-sea hemichordates Torquaratoridae gen. sp. reach high abundance up to 12 spec. m^-2 at the depths of 1830-2130 m on the slope of the Volcanologists Massif in the south-western part of the Bering Sea, dominating in the benthic community at these depths. Their abundance exceeds by two orders the values recorded earlier. In order to clarify this phenomenon, we examined the gut contents of Torquaratoridae gen. sp. The detritus particles and frustules of planktonic diatoms Thalassiosira, Coscinodiscus, Actinocyclus, Chaetoceros, Neodenticula, and Grammatophora were the most common in the gut, as well as the remains of skeletons of benthic invertebrates with little admixture of mineral particles. According to obtained data, Torquaratoridae gen. sp. are mobile deposit feeders with high selectivity to fresh phytodetritus, able to compete with holothurians occupying similar trophic niche. Unusually high abundance of acorn worms is apparently related to high organic matter flux to the seafloor as a result of spring phytoplankton bloom in the surface water layer of the Bering Sea.