Methanotrophic bacterial symbionts fuel dense populations of deep-sea feather duster worms (Sabellida, Annelida) and extend the spatial influence of methane seepage

Deep-sea methane seeps are dynamic sources of greenhouse gas production
and unique habitats supporting ocean biodiversity and productivity. Here,
we demonstrate new animal-bacterial symbioses fueled by methane, between
two undescribed species of annelid (a serpulid Laminatubus and sabellid
Bispira) and distinct methane-oxidizing Methylococcales bacteria. Worm
tissue delta 13C of -44 to -58 per mil suggested
methane-fueled nutrition for both species and shipboard experiments
revealed active assimilation of 13C-labelled CH4 into animal biomass,
occurring via engulfment of methanotrophic bacteria across the host
epidermal surface. These worms represent a new addition to the few animals
known to intimately associate with methane-oxidizing bacteria, and further
explain their enigmatic mass occurrence at 150-million-year-old fossil
seeps. High-resolution seafloor surveys document significant coverage by
these symbioses, beyond typical obligate seep fauna. These findings
uncover novel consumers of methane in the deep-sea, and by expanding the
known spatial extent of methane seeps, may have important implications for
deep-sea conservation.