Wooden steps to shallow depths: A new bathymodiolin mussel, Vadumodiolus teredinicola, inhabits shipworm burrows in an ancient submarine forest

Large mussels of the mytilid subfamily Bathymodiolinae are common
inhabitants of deep-sea hydrothermal vents and cold seeps, where
gill-borne symbionts allow them to utilize energy-rich compounds such as
hydrogen sulfide and methane to support abundant growth. This subfamily
also includes smaller symbiont-bearing mussels found on deep-sea wood and
organic deposits. Phylogenetic analyses suggest that wood association is
ancestral to bathymodiolin evolution. This observation led to the “wooden
steps” hypothesis, which proposed that wood and other large organic
deposits have acted as evolutionary steppingstones, introducing the
progenitors of the modern vent and seep Bathymodiolinae to their remote
environments. Although this hypothesis implies an evolutionary trajectory
from shallow to deep water, no bathymodiolin species that grows and
reproduces at depths less than 100 m has yet been formally described. Here
we describe a new bathymodiolin genus and species, Vadumodiolus
teredinicola, found growing and reproducing at a depth of 18 m in
uninhabited shipworm burrows in the remnants of an ancient submerged bald
cypress forest off the coast of Alabama. These results demonstrate that
the bathymodiolin radiation has not been limited to deep water and that
specific association with wood has led to the successful invasion of both
deep and shallow marine environments.