Meeting Abstract
Abiotic factors of deep-sea habitats such as high hydrostatic pressure and cold temperatures act profoundly on organisms invading these realms. Many fishes use gas bladders for buoyancy, and species living in the deep-sea deal with increased gas compression and density in these highly pressurized systems. Despite this, many retain small gas bladders and may employ other adaptations to aid in buoyancy. One possible mechanism includes decreasing bone mineralization in dense skeletal tissues. To test if there is an association with bone density and depth, Micro-computed tomography scanning was performed on 11 species in the Family Macrouridae (grenadiers) spanning a wide range of habitat depths (100 to 7,000 m). Scans included two hydroxyapatite phantoms as known-density standards to correlate voxel brightness to bone density. Density was compared across four bones (i.e. 11th vertebra, pelvic girdle, lower jaw, 1st pterygiophore), across maximum depths, and within a phylogenetic framework. Bone density varied within macrourid specimens, with the lower jaw being significantly denser than other bones; and was highly variable between species. There was also no correlation between bone density and depth, or between bone density and phylogenetic relationships. Previous work examining adaptations in deep-sea fishes describes trends of reduced skeletal mass, but we found no correlation between bone density and depth in the wide-ranging grenadiers. This lack of correlation could be explained by other adaptations such as reduced skeletal elements or increased lipid storage that may supplement buoyancy in the grenadiers. It is also possible that the lack of bone loss with depth may be revealing a more complicated story. Given the variation and questions raised by this study, quantifying bone density across depth and phylogeny is worth a substantial investigation.
