Edith Cowan University Research Online Theses: Doctorates and Masters Theses 2017 Investigating the effects of changes in light quality on different life history stages of seagrasses Simone Strydom Edith Cowan University Follow this and additional works at: https://ro.ecu.edu.au/theses Part of the Ecology and Evolutionary Biology Commons, and the Marine Biology Commons Recommended Citation Strydom, S. (2017). Investigating the effects of changes in light quality on different life history stages of seagrasses. https://ro.ecu.edu.au/theses/1995 This Thesis is posted at Research Online. https://ro.ecu.edu.au/theses/1995 Edith Cowan University Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorize you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. 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I Investigating the effects of changes in light quality on different life history stages of seagrasses Simone Strydom Bachelor of Environmental Science (Hons) This thesis is presented in fulfilment of the requirements for the degree of Doctor of Philosophy Centre for Marine Ecosystem Services School of Science Edith Cowan University 2017 Use of Thesis This copy is the property of Edith Cowan University. However the literary rights of the author must also be respected. If any passage from this thesis is quoted or closely paraphrased in a paper or written work prepared by the user, the source of the passage must be acknowledged in the work. If the user desires to publish a paper or written work containing passages copied or closely paraphrased from this thesis, which passages would in total constitute an infringing copy for the purposes of the Copyright Act, he or she must first obtain the written permission of the author to do so. Declaration I certify that this thesis does not, to the best of my knowledge and belief: i.Incorporate without acknowledgment any material previously submitted for a degree or diploma in any institution of higher education; ii. Contain any material previously published or written by another person except where due reference is made in the text of this thesis; or iii. Contain any defamatory material. Signature: Date: 28th April 2017 II Acknowledgements I am grateful to the Australian Postgraduate Award Scheme and the Western Australia Marine Science Institution for the generous scholarships they awarded. Funding from the Western Australian Marine Science Institution (WAMSI, Dredging Science Node), Woodside Energy, Chevron Australia, and BHP Billiton as environmental offsets and by co-investment from the WAMSI Joint Venture partners provided crucial funds that were used to build, maintain and run all experiments throughout this project. The commercial investors had no role in the data analysis, data interpretation, and the decision to publish or in the preparation of any part of this thesis. I would also like to thank Hillarys Rotary Marine Club, Holsworth Wildlife Research Endowment (Equity Trust), Graduate Women of Western Australia, In-Situ Marine Optics, World Seagrass Association, Edith Cowan University School of Science and the Centre for Marine Ecosystems Research for their support and funding towards conference attendance, equipment purchases, sample analysis and field costs associated this project. I am also particularly grateful to Kathryn McMahon and Paul Lavery for providing a writing up scholarship towards the end of my degree. I am indebted to Caitlin Rae, Roisin McCallum, Nicole Said, Natasha Dunham and Paul Armstrong for their help with field, laboratory and aquarium work. I would also like to respectfully acknowledge Catherine Collier for passing on her well-developed laboratory protocols, and to Michael Durako and Michael Rasheed for providing exceptionally valuable feedback on my PhD proposal. I was fortunate enough to have the ultimate supervisory panel: Dr. Kathryn McMahon, Prof. Paul Lavery, Prof. Gary Kendrick and Dr. John Statton. Together they provided a far-reaching breadth of expertise and I learned a great deal from each and every one of them. I would specifically like to thank Kathryn and Paul for providing unwavering support and encouragement throughout my degree; I will miss our weekly fruitful discussions. Kathryn, I am grateful for being given the opportunity to observe and learn from your comprehensive seagrass biology knowledge, systematic problem solving and critical thinking skills. I am in awe of how you conduct yourself with sincere equanimity whilst maintaining your wonderful, genuine nature. You are an inspiration and I can only strive to amount to half the scientist you are one day. Thank you Paul for greeting me and every other student, who incessantly knocked on your office door, with a smile. Your patience, eagerness, passion and knack for explaining concepts in “student language” are unparalleled. You were the first academic I felt comfortable “challenging” and from that, I have learned diplomacy – an unexpected, but necessary skill in research. I would also like to express my gratitude towards John Statton for his practical advice on all seed, aquarium and PAM related III issues. Your approachable demeanour always made our interactions a breeze and I am really appreciative that you never made me feel like I asked a stupid question (which I definitely did). Only someone with such a light-hearted nature and great sense of humour could turn three days of moving five tonnes of sand by hand into a joyous occasion. I am grateful also to Gary Kendrick for his challenging yet supportive method of supervision. You always made me feel part of the UWA team and your ability to think outside the box always led to such insightful conversation. And if there was a spanner readily available to throw in the works, it often came hurtling from Gary’s general direction – I am a better scientist for it, thank you. On a personal note, I would like to thank Jeramie Putman for your unprecedented patience, encouragement and for lending me the use of your steadfast logical brain during times when my fatigued grey matter would cooperate no longer. I am ever-grateful for your endurance of the chilly Perth water in the name of saving seagrasses. I thank you for helping me with data entry, weighing samples, moving aquaria, counting seeds, tagging ramets, cleaning aquariums and your mind reading skills when it came to coffee making. To have made this journey with you at my side has been the greatest gift of all – I owe you more than I could ever hope to repay. Lastly, I am indebted to Sandra Warren for taking a truly difficult leap to immigrate to this beautiful country which supported my tertiary education. That one action facilitated the fulfilment of a tenacious six year old girls’ dream of one day becoming a marine biologist. Whilst we were always separated by distance, your life lessons, the good and the bad, were never far from my mind. IV Abstract Seagrass meadows provide crucial ecosystem services to the coastal zone but globally are threatened. Seagrass loss to date has mainly been attributed to anthropogenic activities that reduce light quantity, such as dredging, declining water quality from urban and agricultural run- off and eutrophication. However, light quality (wavelengths of light) is also altered by these anthropogenic stressors as well as natural events. This study consisted of three main components: (1) characterising light quality to which seagrasses are exposed across a local natural estuarine-ocean gradient and with a human impact pressure; (2) the influence of monochroma -2 -1 nm wavelengthstic light and quality full- (blue λ=451 nm; green– 700λ=522 nm, nm; at yellow 200 µmol λ=596 photons nm and m red sλ=673) on Halophila ovalis and Posidoniaspectrum australis light at differentλ=400 life-history stages; and the effects of light -1 quality and quantity representative of (3) -2 -1 200 µmol photons m s ) on H. ovalis adulta commercial plants. The dredging field work operation demonstrated (15 mg thatL TSS, the quality50 and of light to which seagrasses are exposed varies along a natural gradient but the nature of the shift is also dependent on time of year. Additionally, human impact such as dredging can expose seagrasses to spectra outside of the natural range detected in this study, and the magnitude of this shift is dependent on depth and TSS concentrations. Results from the monochromatic light quality experiments demonstrated, for the first time, the seagrass responses to light quality across several plant scales as well as different life-history stages. Halophila ovalis and P. australis showed different responses, likely due to their respective growth strategies. Adult H. ovalis (a colonising species) plants were negatively impacted by monochromatic blue, green and yellow light treatments, while seeds and seedlings performed better under red and full-spectrum light. Conversely, P. australis (a persistent species) adults showed no significant responses to any of the monochromatic light quality treatments, while seedlings demonstrated a physiological acclimation to blue light.