Horak Robin V.

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Horak
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Robin V.
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  • Preprint
    Hypotaurine and thiotaurine as indicators of sulfide exposure in bivalves and vestimentiferans from hydrothermal vents and cold seeps
    ( 2006-08-24) Brand, Garth L. ; Horak, Robin V. ; Le Bris, Nadine ; Goffredi, Shana K. ; Carney, Susan L. ; Govenar, Breea ; Yancey, Paul H.
    Vesicomyid clams, vestimentiferans, and some bathymodiolin mussels from hydrothermal vents and cold seeps possess thiotrophic endosymbionts, high levels of hypotaurine and, in tissues with symbionts, thiotaurine. The latter, a product of hypotaurine and sulfide, may store and/or transport sulfide non-toxically, and the ratio to hypotaurine plus thiotaurine (Th/[H+Th]) may reflect an animal's sulfide exposure. To test this, we analyzed seep and vent animals with in situ sulfide measurements. Calyptogena kilmeri clams occur at high-sulfide seeps in Monterey Canyon, while C. (Vesicomya) pacifica clams occur at seeps with lower levels but take up and metabolize sulfide more effectively. From one seep where they co-occur, both had gill thiotaurine contents at 22-25 mmol/kg wet mass, and while C. (V.) pacifica had a higher blood sulfide level, it had a lower Th/[H+Th] (0.39) than C. kilmeri (0.63). However, these same species from different seeps with lower sulfide exposures had lower ratios. Bathymodiolus thermophilus (East Pacific Rise [EPR 9°50'N]) from high- (84 μM) and a low- (7 μM) sulfide vents had gill ratios of 0.40 and 0.12, respectively. Trophosomes of Riftia pachyptila (EPR 9°50'N) from medium- (33 μM) and low- (4 μM) sulfide vents had ratios of 0.23 and 0.20, respectively (not significantly different). Ridgeia piscesae vestimentiferans (Juan de Fuca Ridge) have very different phenotypes at high- and low-sulfide sites, and their trophosomes had the greatest differences: 0.81 and 0.04 ratios from high- and low-sulfide sites, respectively. Thus Th/[H+Th] may indicate sulfide exposure levels within species, but not in interspecies comparisons, possibly due to phylogenetic and metabolic differences. Total H+Th was constant within each species (except in R. piscesae); the sum may indicate the maximum potential sulfide load that a species faces.