Commensalism between Juvenile Cusk Eels and Pancake Urchins on Western North Atlantic Seamounts

We describe a commensal relationship between small (approximately 6 to 9 cm) deep-sea cusk eels, one tentatively identified as Barathrites sp. (Osteichthyes: Ophidiidae), and pancake urchins, both Hygrosoma petersi and Phorosoma placenta (Echinodermata: Echinothuriidae). These interactions were observed in situ using a remotely operated vehicle (ROV), deployed at depths of 1410 to 1775 m on three seamounts in the western North Atlantic (Bear and Rehoboth seamounts in the New England Seamounts and Yakutat Seamount in the Corner Rise Seamounts). Full motion video and still frames documented individual cusk eels associated with urchins in open fine-grained sediment and coral rubble habitats. Cusk eels foraged around the periphery of urchins and took refuge at the base and among the long spines on the aboral surface. We suggest that such associations provide juvenile cusk eels with shelter from predators or flow (or both) and access to prey far from other forms of refugia.