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To request permissions please use the Feedback form on our webpage. http://researchspace.auckland.ac.nz/feedback General copyright and disclaimer In addition to the above conditions, authors give their consent for the digital copy of their work to be used subject to the conditions specified on the Library Thesis Consent Form and Deposit Licence. Enhancing larval survival and re-introduction techniques for Tridacnidae (giant clams): Reversing a path toward extinction Charles George Waters Institute of Marine Science University of Auckland A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in Marine Science, The University of Auckland, 2014 Abstract Mariculture interest in the Tridacnidae family of giant clams has increased in response to economic and nutritional opportunities, but also in response to increasing reports of local extinctions as a result of over-harvesting, pollution, and habitat degradation. Key impediments to culturing giant clams for stock restoration initiatives include larval mortality, typically ≥ 96%, and a lack of methods for re-introducing juveniles to natural habitats. This thesis studied how nutritional conditions during early development influenced giant clam survival and growth, and how survival can be increased when juveniles are recruited directly to coral substrata. Information about the nutritional condition of pre-veliger tridacnids is scarce. A review of pre-veliger nutrition revealed that broodstock feeding, water temperature, oocyte maturity, and dissolved organic matter (DOM) loading in culture water influences larval viability. An experiment to measure the effects of parental conditioning on egg size and biochemical composition showed that feeding Tridacna maxima parents a high-lipid, high-protein diet for 5 weeks prior to spawning increased egg volumes by >13%, and that survival compared to unfed cohorts nearly doubled. However, the effects of parental feeding on egg lipid classes and volumes were inconclusive. Increased bivalve egg size is known to influence larval survival. A protocol was tested for selecting T. maxima eggs by size to increase survival. Results showed that mean egg sizes for two T. maxima was 101.3 µm ± 0.17 (n = 284). However, segregating eggs by size above and below 100 µm proved futile since egg jelly coats ranging from 160 µm to 202 µm interfered with the sieving procedure. Tridacnids take up nutrition in the form of DOM and amino acids during veliger stages of development, but when this process begins was unknown. Experiments conducted on T. maxima and Tridacna squamosa in filtered seawater compared to artificial, nutrient- free seawater showed that uptake begins much earlier than previously thought. In addition to increased survival, trochophore growth increased 50% and 76% for T. maxima and T. squamosa , respectively in response to the availability of DOM and 0.4 µ M and 0.8 µ M amino acid concentrations. There is debate among tridacnid hatchery managers as to whether veligers should be fed supplemental nutrients. A review of the literature and protocols currently in place showed that supplemental feeding tends to enhance veliger survival and growth, and that the gap between cost and effect is closing. However, risks such as algal overgrowth, bacterial infection, and increased biochemical oxygen demand remain. A field experiment was conducted to determine if reducing predation pressure and water turbulence on juvenile T. maxima recruited directly to coral substrata increased ii survival. Protective cages were tested on one-, two- and three-year-old T. maxima juveniles for three weeks. Survival of three- year-olds in triplicate cages was 100%, 96% and 76% compared to 40% in unprotected controls. Survival of one-year-olds was 40%, 54%, and 63% compared to 15% in controls, suggesting that two- and three-year-olds are favoured for survival. This thesis shows for the first time that pre-veliger nutrition is critical to larval viability, and that survival can be increased for two- and three-year-old juveniles recruited directly to lagoon substrata. iii Dedication and Acknowledgements This dissertation is dedicated to Margaret M. Bächtold, Dr. Livia D’Andrea, and Dr. John Bächtold. Many people deserve far more than acknowledgement. Special thanks are extended to Drs. Mark Costello and Andrew Jeffs at the University of Auckland, Institute of Marine Science (IMS), for the opportunity to pursue my studies at such a young stage in life. As my primary supervisor, Dr. Costello provided standards for scholarship, rigor, and critical analyses that any student would cherish. A special thank you goes to Dr. Grace Sparks, the professor whose contagious passion for natural science helped rescue me from computer science. Sincere appreciation is extended to Drs. Clyde Barlow, Heather Heying, and Tim Quinn for their support, guidance, and encouragement. At the University of Auckland, I am grateful for the unselfish support and inspiration from Dr. Bill Ballantine, Martin Middleditch, John Lavas and Erica Zarate, and Drs. Anthony Hickey, Shane Lavery, Adrian Turner, Brian Dobson and Clive Evans. Fellow students Zeenatul Basher and Hanieh Saeedi have been steady sources of support and cherished companionship. Thanks are due to Richard Story and his staff at the Aitutaki Marine Research Centre, Steve Lindsay, and Dr. Rick Braley for their support and expert advice on all things related to giant clams. Thanks are also due to Evan Needham, Dr. Ann Fleming, and the remarkably supportive staff at the Darwin Aquaculture Centre. Peter Robinson, Jenna Nelson, Ladd Rutherford III, Greg Dasso, Marty Beagle, Nicole Allen, Shane Peterson, Michelle Bartlett, and Drs. Eric Thuesen and Maria Bastaki at The Evergreen State College cannot be thanked enough for their support and encouragement during the formative years. I am indebted to Drs. Norman Ragg and Zoe Hilton at the Cawthron Research Institute for their insights and encouragement. Special thanks are extended to Tracy Rose for her invaluable critical and grammatical reviews of my manuscripts along the way, and to Robin and Graham Radford, whose friendship and generosity has made my tenure in New Zealand infinitely more enjoyable. Finally, many thanks to the University of Auckland Scholarship Committee for reducing the financial pressures associated with doctoral research. iv Table of Contents Table of Contents Abstract....................................................................................................................................... ii Dedication and Acknowledgements ........................................................................................... iv Co-Authorship Forms................................................................................................................ vii 1.0 GENERAL INTRODUCTION ...........................................................................................2 1.1 Introduction..................................................................................................................2 1.2 Biology and ecology ....................................................................................................2 1.3 Socio-economics .........................................................................................................4 1.4 Ecological status..........................................................................................................4 1.5 Tridacnid larval development.......................................................................................5 1.6 Project origins............................................................................................................13 1.7 Research aims...........................................................................................................14 2.0 FACTORS RELEVANT TO PRE-VELIGER NUTRITION...............................................16 2.1 Introduction................................................................................................................16 2.2 Dissolved organic matter (DOM)................................................................................23 2.3 Optimizing pre-veliger nutrition ..................................................................................25 2.4 Reproductive patterns................................................................................................28 2.5 Discussion .................................................................................................................32 3.0 EFFECTS OF PARENTAL FEEDING ON LARVAL VIABILITY .....................................35 3.1 Introduction................................................................................................................35 3.2 Materials and Methods ..............................................................................................38