DOCTOR OF PHILOSOPHY Trophic relevance of gelatinous zooplankton for commercial fisheries in the Irish Sea Griffin, Donal Award date: 2020 Awarding institution: Queen's University Belfast Link to publication Terms of use All those accessing thesis content in Queen’s University Belfast Research Portal are subject to the following terms and conditions of use • Copyright is subject to the Copyright, Designs and Patent Act 1988, or as modified by any successor legislation • Copyright and moral rights for thesis content are retained by the author and/or other copyright owners • A copy of a thesis may be downloaded for personal non-commercial research/study without the need for permission or charge • Distribution or reproduction of thesis content in any format is not permitted without the permission of the copyright holder • When citing this work, full bibliographic details should be supplied, including the author, title, awarding institution and date of thesis Take down policy A thesis can be removed from the Research Portal if there has been a breach of copyright, or a similarly robust reason. 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Oct. 2021 Declaration I declare that: (i) The thesis is not one for which a degree has been or will be conferred by any other university or institution; (ii) The thesis is not one for which a degree has already been conferred by this university; (iii) The work for the thesis is my own work and that, where materials are submitted by me for another degree or work undertaken by me as part of a research group has been incorporated into the thesis, the extent of the work thus incorporated has been clearly indicated; (iv) The composition of the thesis is my own work The format of this thesis is in accordance with the guidelines published by Queen’s University of Belfast. Donal Christopher Griffin June 2019 1 Trophic relevance of gelatinous zooplankton for commercial fisheries in the Irish Sea 2 Acknowledgements I would like to thank everyone who has helped me complete this PhD; the list is long. Firstly, thank you to my supervisors. Dr Jonathan Houghton and Dr Chris Harrod who I have known since my undergraduate degree. Your expertise and advice have helped me become not only a better scientist but a better person. I appreciate everything you have done for me, not least your patience in guiding me to the completion of this thesis. For that I will always be grateful. To my third supervisor Dr Steven Beggs, the time I spent on the AFBI research ship are some of my happiest memories of the PhD. Without your effort and help in the field this PhD would not have been possible, thank you. A huge thank you to AFBI and all the crew and scientific staff on the RV Corystes who let me ‘piggy-back’ on their surveys and collect the data contributing to this thesis. Thank you to the funders and match funders of this PhD including DAERA NI, AFBI NI, NERC, QML who made this PhD project possible. Thank you to all my collaborative partners who have helped me carry out the various aspects of this multidisciplinary thesis including; Victoria Dominguez Almela and Dr Christophe Eizaguirre from Queen Mary London University, NERC Life Sciences Mass Spectrometry Facility at Bristol University, University of Hull. Special thanks to Dr Isabella Capellini, Dr Jason Newton and Alison Kuhl who introduced me to whole other worlds of scientific techniques and methods, and for your never-ending patience in helping me to use those to answer my jelly related questions. I would also like to thank Gillian Riddell for her field work know how and help throughout my time at QUB, for being a good friend during the darkest times of my PhD and for organising various field courses I attended at undergraduate level. Those courses are the reason I chose to become a marine biologist, and for that I will always be grateful. I would like to thank my friends. I would not be here without you all. This PhD has produced some of the best and worst times of my life and whether you realise or not, you all have been the constant I needed to keep going. A special thanks to those who read over drafts of my thesis, I owe you a large bottle of gin. Finally, I want to thank my family. Mum, Patrick, Kym and Lockie. I love you all and appreciate everything you have ever done for me. I am a better person because of your kindness, patience and generosity, thank you! 3 Abstract Jellyfish can compete with fish for food resources, or feed on fish eggs and larvae. They also provide habitat and space for developing larval and juvenile fish which use their hosts as means of protection from predators and feeding opportunities. However, the broader ecological relevance of jellyfish is often neglected beyond their role as stressors to the marine environment, including fish communities. However, this is a gross over-simplification of the true role of jellyfish in the marine environment, yet the link between field biologists and modellers remains a limiting factor in their inclusion in ecosystem and fisheries models. Using a multidisciplinary approach, this thesis aimed to provide a balanced understanding of the net impact of jellyfish on fish communities in the Irish Sea, and to provide a means for researchers to do the same in marine systems around the world. Chapter one of this thesis is a broad synthesis of the traditional, as well as the more recent and nuanced view of the role of jellyfish in the marine environment. Chapter two employs comparative phylogenetic techniques and indicates that jellyfish association is a probable adaptive anti-predator strategy for juvenile fish, more likely to evolve in benthic (fish living on the sea floor), benthopelagic (fish living just above the bottom of the seafloor) and reef-associating species than those adapted to other marine habitats. Latter experimental chapters predominantly employ trophic investigation and analysis to assess fish-jellyfish predator-prey interactions in the Irish Sea. Chapter three investigates jellyfish inter-tissue isotopic variation and discusses whether tissue and/or size-based isotopic grouping are suitable parameters for the inclusion of jellyfish in ecosystem, fisheries and food web models in the future. Evidence for inter-tissue δ15N variation within and across scyphozoan jellyfish species is provided. Furthermore, findings indicate how δ15N may be influenced by jellyfish size, which in certain instances may be a useful tool in accounting for the nuances of jellyfish trophic ecology. Chapter four employs the latest Bulk Stable Isotope Analysis (BSIA) and Compound Specific Isotope Analysis (CSIA) techniques to quantify robust jellyfish Trophic Discrimination Factors (TDFs) to aid the estimation of jellyfish Trophic Position (TP). Findings suggest that estimates based on a bulk TDF of 2.9‰ and an amino-acid TDF of 7.6‰ overlapped 4 for all comparisons indicating that these TDF values may be appropriately representative of jellyfish: allowing for their inclusion in isotopic food web studies in the future. In the last experimental chapter, we used jellyfish appropriate TDFs to resolve jellyfish trophic positions and explore the role of jellyfish in an Irish Sea food- web context. More specifically we explored whether trophic fish-jellyfish interactions are a two-way street i.e. do fish eat jellyfish and do jellyfish eat fish. Finally, in chapter six we bring together all the strands of the thesis and discuss the broader relevance of the findings. As pressure on fin-fish stocks increase year on year due to overfishing, habitat disturbance and climate change, acknowledging and accounting for additional but lesser known factors such as fish-jellyfish interactions such as two-way predation is important to inform and safeguard sustainable fisheries and fishing in the future. More specifically, to ignore fish-jellyfish interactions and their trophic importance in marine systems and food webs, runs the risk of misrepresenting the ecological role of a broad array of species, not least commercial fish upon which jellyfish can impact both negatively and positively. 5 Contents Declaration ................................................................................................................................. 1 Trophic relevance of gelatinous zooplankton for commercial fisheries in the Irish Sea ......... 2 Acknowledgements .................................................................................................................... 3 Abstract ...................................................................................................................................... 4 Contents ...................................................................................................................................... 6 List of appendices ..................................................................................................................... 10