Biotic and abiotic interactions of deep-sea hydrothermal vent-endemic fish on the East Pacific Rise

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2009A study of the ecology of fish endemic to hydrothermal vents on the East Pacific Rise was undertaken utilizing a variety of techniques, focusing on the bythitid Thermichthys hollisi. Stable isotope and gut content analyses were used to elucidate prey choice and trophic relationships. Otolith chemical signatures were investigated to determine whether this technique could be utilized to examine life history strategy and habitat use. Chemical characteristics of preferred fish habitat and gene expression responses habitat chemistry were explored. Gut contents indicated that T. hollisi specimens were actively feeding upon a combination of brachyuran crabs, Alvinocaris shrimp, polychaetes, and zoarcid fish with the majority of fish containing evidence of crustacean prey. Carbon, nitrogen, and sulfur stable isotopic measurements support a chemosynthetically based prey source and place T. hollisi in the uppermost trophic levels of vent communities. The influence of exposure to hydrothermal fluids was apparent in otoliths from both species of vent fish, most noticeably within the relatively elevated Sr:Ca and depleted Mg:Ca ratios. Otolith chemistry suggested that the zoarcid Thermarces cerberus experiences greater direct exposure to diffuse fluids than does T. hollisi, which is concurrent with apparent habitat preferences. Isotopic patterns across the span of the otolith suggested that T. cerberus spends its entire life within the vent system. In contrast, it appeared that T. hollisi exists outside of the influence of hydrothermal activity for some early portion of its life-cycle. Time-lapse photography and in situ electrochemistry indicated that T. hollisi are preferentially utilizing fish holes where there are elevated temperatures and sulfide levels, and variable oxygen levels in comparison to ambient bottom water. A fragment of Cu, Zn superoxide dismutase was successfully amplified from T. hollisi mRNA, but there were no differences in expression levels between tissue types or among individuals within the small sample examined. In general, it appears that T. hollisi is both influenced by and may exert a greater influence on hydrothermal vent communities to a greater degree than initially hypothesized.I was the recipient of a 2003 MIT Presidential Fellowship, a 2004-2007 National Defense Science and Engineering Graduate Fellowship, and received support from the Woods Hole Oceanographic Institution Academic Programs Office as well as National Science Foundation’s Office of Polar Programs (ANT-073965) support to TMS. Funding for my research was provided in part by the National Science Foundation (OCE-032726 and OCE-0324232), the National Oceanic and Atmospheric Administration’s Office of Ocean Exploration and Research (Award Nos. NA03OAR4600110, NA16RP2390, and NA 04OAR4600049) support to TMS and a 2008 Lerner-Gray Grant for Marine Research from the Lerner Gray Memorial Fund of the American Museum of Natural History support to KLB