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

Abstract

A 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.Thesis Supervisor: Timothy M. Shank Title: Associate Scientist, Biology Department, Wood Hole Oceanographic Institution Ackiowledgements This thesis could not have been accomplished without the support of a variety of people who have been there for me both personally and professionally throughout the past six years. My advisor, Tim, has provided me with innumerable opportunities to expand my horizons, and has always allowed me the freedom to pursue my own interests, even if the road I wanted to go down was not what many would have viewed as the logical choice. When he realized that yes, I really only wanted to work on fish, he helped make that dream a reality. He and the rest of my committee: Simon, Mark, Leona, and George, have always been helpful, supportive, and willing to answer any questions that I might ha...

Parasite diversity at isolated, disturbed hydrothermal vents

“…The extent to which vent fishes move among vent fields is unknown; however, all available evidence suggests that they are closely associated with vent ecosystems. The feeding spheres of the two fish species at EPR 9N, T. cerberus and T. hollisi, have been inferred from otolith chemistry [42] and gut contents [73] and are unlikely to extend into adjacent habitats or other depths in the water column [63]. Extreme, frequent disturbance is another factor expected to reduce parasite richness at EPR 9N vents.…”

“…During these cruises, we were only able to collect limited numbers of the two endemic fish species at EPR 9N (nine Thermarces cerberus and two Thermichthys hollisi). We supplemented our data with fish specimens collected from the same sites during prior cruises: two whole T. cerberus from 2017 and guts of 22 T. hollisi from 2007 [42].…”

“…Second, vent communities have relatively simple food webs and a low number of vertebrate predator species [41]. For example, vent fields on the northern EPR have only two endemic fish species [42]. Parasite taxa with ILCs have one or more life stages that pass up food chains when one host consumes another.…”