Spatial Patterns in Macro-Consumers of the Mid-Atlantic and East Scotia Ridges
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Trophodynamics on Mid-Ocean Ridges: spatial patterns in macro-consumers of the Mid-Atlantic and East Scotia Ridges William David Kenneth Reid A Thesis submitted to Newcastle University for the Degree of Doctor of Philosophy School of Marine Science & Technology Supervisors: Dr Ben D Wigham Prof. Nicholas V C Polunin Examiners: Prof. George Wolff (University of Liverpool) Dr Richard Bevan (Newcastle University) Submitted: October 30th 2012 Breton Fisherman’s Prayer Dear God, Be good to me, The sea is so wide, And my boat is so small. Abstract Abstract The 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. i Abstract 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. ii Acknowledgements Acknowledgements I embarked on this PhD knowing it would be an adventure: exploring underwater water mountain ranges, working in frontal regions in the North Atlantic Ocean, research surveys to the Antarctic and using scientific equipment at the forefront of UK deep- water research. I think I should start by acknowledging Ben Boorman of National Oceanography Centre, Southampton (NOCS) for his expertise in trawling on the Mid- Atlantic Ridge and Dave Turner and his ROV team (NOCS) for their skill in ROV operations. Without these dedicated people I would not have collected the samples for this PhD. I would like to thank my supervisors Dr Ben Wigham and Prof. Nicolas Polunin for all their help and support throughout the PhD. It was not the most-straight forward of PhD’s due to postponement of research cruises, delays in sample return from the Antarctic and an unsuccessful foray into the world of lipids. Their guidance and encouragement has been invaluable, I have learnt so much and enjoyed working with them. I would like to thank members, past and present, within the research group at Newcastle University, especially Dr Benjamin Kurten for advice on stable isotopes and Dr Aileen Mill for advice on stable isotopes and statistics. A big thank you has to be given to Dr Chris Sweeting for his advice, interesting discussions on all aspects of isotope methodology and ecology, help with writing grant proposals and reading through various pieces of work. Further people who need my thanks out with the research group are Dr Kate Broughton and Dr Gordon Port for using their micro-balance and Dr Martin Edwards for freeze drying samples for me. iii Acknowledgements This PhD was involved in the ECOMAR and ChEsSo NERC funded consortium projects and there is a long list of who have helped me in the last four years. Firstly, within the ECOMAR I would like to thank Prof. Monty Priede (University of Aberdeen) for inviting me on two ECOMAR cruises to the Mid-Atlantic Ridge. I was assisted with sample collection on these trips by Dr Ben Wigham, Andrew Oliphant and Gary Robinson (both Newcastle University) along with various other scientists who were sorting trawls and carrying cores. Special mentions go to Dr Nikki Cousins (University of Aberdeen) for co-ordinating the deep-sea fish identifications and providing advice on their ecology, Claudia Alt for co-ordinating the invertebrate identifications from the trawl samples, and Dr Tracy Schimmield and Dr Richard Abell for providing sediment trap samples. Secondly, within the ChEsSo project I would like to the thank Prof. Alex Rogers (University of Oxford) and Prof. Paul Tyler (University of Southampton) as PIs on the two ChEsSo cruises, Dr Katrin Linse (British Antarctic Survey) for co-ordinating the sample sorting and identifications, Dr Katrin Zwirglmaier (formally of BAS now Technical University Munich, Germany) for always keeping me up-to-date with progress on the identification of epi- and endo-symbionts of the invertebrates, and Leigh Marsh (University of Southampton) for providing information on the spatial distribution of vent organisms at each site. Finally, a thank you to all those I sailed with on the R.R.S James Cook including the Captains, crew, chiefs and scientists who made each trip memorable. The stable isotope analysis was undertaken at Iso-Analytical (Cheshire, UK) by Steve Brookes and his team and at SUERC (East Kilbride) by Rona McGill. I visited SUERC on numerous occasions and was always made to feel welcome. Thanks you to Rona McGill who taught me some of the ins and outs of isotope ratio mass spectrometry. iv Acknowledgements I would like to thank Dr Andrew Jackson (Trinity College, Dublin) for his statistical assistance in Chapter 5. This involved help with writing the code for the R statistical programme and taking the time to run through interpretation the results. I’m grateful to Dr Odd Askell Bergstad and Dr Tone Falkenhaug (Institute of Marine Research, Norway) and Dr Tracey Sutton (VIMS) for their support through the MAR- ECO network as well as MAR-ECO for providing funds to attend workshops and the Deep-Sea Biology Symposium in Iceland. 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 never have completed this without your love. v Table of contents Table of contents 1. Introduction....................................................................................... 1 1.1. The deep-sea ecosystem.................................................................. 2 1.2. Food chains and webs: a fundamental ecosystem process.............. 3 1.3. Investigating trophodynamics......................................................... 5 1.3.1. Stable isotope analysis.......................................................... 6 1.3.2. Isotopic turnover rates of tissues.......................................... 11 1.4. Productivity, food sources and their influence on the deep sea...... 12 1.4.1. Food inputs and the response of non-vent deep-sea fauna... 13 1.4.2. Influence of food quantity and quality on benthic abundance & biomass.............................................................. 16 1.4.3. Hydrothermal vents and their food sources.......................... 17 1.4.4. Global variation in hydrothermal vent habitats and communities............................................................................. 19 1.5. The role of body size in trophodynamics........................................ 20 1.6. Mid-ocean ridges, study sites and thesis objectives........................ 23 1.6.1. Mid-ocean ridges (MOR)..................................................... 23 1.6.2. Mid-Atlantic Ridge............................................................... 26 1.6.3. East Scotia Ridge.................................................................. 27 1.6.4. Thesis outline and objectives................................................ 29 2. Elucidating benthic and pelagic trophic pathways in deep-sea assemblages of the Mid-Atlantic Ridge north and south of the Charlie-Gibbs Fracture Zone........................................................... 31 2.1. Introduction..................................................................................... 32 2.2. Methods........................................................................................... 35 vi Table of contents 2.2.1. Study sites............................................................................