PhD ThesisThe global mid-ocean ridge (MOR) system is ~60 000 km long and accounts for 9% of the seafloor. Deep-sea organisms living on MOR have two potential energy sources; chemosynthesis and the downward flux of photosynthetic organic matter. This study examines the trophodynamics of benthic fauna collected from non-vent sites north and south of the Charlie-Gibb Fracture Zone (CGFZ) on the Mid-Atlantic Ridge (MAR) and hydrothermal vents fields (E2 and E9) on the East Scotia Ridge (ESR) using stable isotopes of carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S).
δ13C and δ34S values revealed the MAR benthos was sustained by photosynthetic primary production and no chemosynthetic food source was detected. δ15N values of benthic invertebrates were lower than the surficial sediments at the southern site but this did not occur at the northern site. Benthic invertebrates appeared to comprise a separate food chain to bentho-pelagic fishes and crustaceans but size-based trends in δ13C and δ15N revealed at certain life history stages bentho-pelagic fishes may consume benthic fauna. Size-based trends in δ13C and δ15N trends varied spatially and temporally in some bentho-pelagic fishes, which suggested differences in feeding plasticity among the species.
Spatial differences among sites were observed in δ13C, δ15N and δ34S of the ESR vent fauna. These were thought to reflect differences in the vent fluid chemistry, vent derived carbon fixation pathways and incorporation of photosynthetic organic matter into the vent system depending on the species and the magnitude of the difference among sites. Size and sex were important determinants of intra-population variability in stable isotope values of three species of vent fauna but this was not consistent among sites.
Abstract
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The present study revealed the importance of undertaking a tri-isotope approach to deep-sea trophic studies in order to elucidate production sources and at different sizes deep-sea organisms can link different trophic pathways.The work was funded by the Natural Environment Research Council and consisted of a studentship NE/F010664/1; sample analysis via Life Sciences Mass Spectrometry Facility grants EK127-10/08, EK150-12/09 and LSMFBRIS043_04/10_R_09/10; ECOMAR consortium grant NR/C512961/1; and ChEsSo consortium grant NE/DO1249X/1.
I’m very grateful to my parents and sister for all the love and support they have given me over the years. Finally, I would like to thank Charlotte. Thank you for your patience, support, encouragement, cups of tea, cooked meals and constantly being there for me whether I was at sea, home or when I thought the PhD was crumbling around me. I could neve