Does the symbiotic scale-worm feed on the host mussel in deep-sea vent fields?

The scale-worm Branchipolynoe pettiboneae is frequently found in the mantle cavity of Bathymodiolus mussels living in hydrothermal vents and seeps around Japan. To investigate its feeding habits and symbiotic relationship with the host mussels, we determined the stable nitrogen isotopic composition of glutamic acid and phenylalanine for representative scale-worms including a symbiotic juvenile and a symbiotic adult, both with their host mussels, and a free-living adult, collected from hydrothermal vents of the Hatoma Knoll (~1532 m in depth) in the Okinawa Trough, Japan. The isotopic data suggested the feeding habits that Bathymodiolus platifrons is a major source of amino acids for symbiotic adult scale-worm but not for free-living adult and symbiotic juvenile scale-worms.