PICKY EATER OR GENERALIST FEEDER? DIET DIVERSITY AND FUNCTIONAL HOMOGENIZATION IN HERBIVOROUS REEF FISHES A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAIʻI AT MĀNOA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN MARINE BIOLOGY (SPECIALIZATION IN ECOLOGY, EVOLUTION, AND CONSERVATION BIOLOGY) May 2020 By Eileen M. Nalley Dissertation ComMittee: Robert J. Toonen, Chairperson Megan J. Donahue Mark A. Hixon Brian W. Bowen AMber N. Wright Keywords: herbivore, specialization, metabarcoding, homogenization © Copyright 2020 – Eileen Nalley All Rights Reserved. i DEDICATION This work is dedicated to Dr. Stephen Karl, who gave me the chance to get started, to Ms. Susan Tittlebaum and Dr. Mary Gubala, who inspired me to pursue a career in science, and to my faMily, who supported and encouraged me every step of the way. ii ACKNOWLEDGEMENTS I would first like to thank Steve Karl for welcoming me into his lab and for opening the door for me to the University of HaWaiʻi. I will alWays be grateful for this opportunity. I also appreciate the mentorship of Rob Toonen and Megan Donahue. Without theM, none of this work Would have been possible. Rob alWays has an ansWer in a tiMe of crisis or a joke in tiMes of calM. He gives so much to his Work and to his students, and it has been such a privilege to work With hiM. Megan’s Willingness to tackle neW ideas and challenges serves as a constant reMinder that the joy of learning never ends, and I aM so thankful for her humor and guidance. I would also like to thank the other meMbers of my comMittee. Brian, Who along with Rob, welcomed Me into the ToBo Lab and provided an aMazing exaMple of what it means to be a great person, in addition to being a great scientist. Mark’s Willingness to coMMunicate outside of acadeMia is an inspiration to students trying to navigate the murky boundaries of science and policy that we face at present. AMber has been supportive and encouraging from the beginning, giving feedback that is alWays insightful and transcends the land-sea boundary. In addition, I would like to thank Adel Heenan, who has been an integral part of much of this dissertation work. Her positivity is a wonder and an inspiration, and I aM so fortunate to have had the chance to work with her. Molly TiMMers and Rachael Wade have also provided so Much feedback and guidance throughout this process. They blazed the way in metabarcoding, and without theM I would have been lost. I also owe a huge debt of gratitude to Richard ColeMan for being willing to share and to Derek Kraft and Julie Zill for their expert fishing skills. I also received help from dedicated undergraduate research assistants (Luis Espinosa, Ryan Shiesha, Sydney Luitgaarden, Madeline Schmidbauer, Alex Mathers, Morgan Pugh, and the OPIHI creW). In addition, I want to thank the residents, facilities, fiscal, and administrative teaMs at the HaWaiʻi Institute of Marine Biology for all that they do. Nothing would happen without theM. I received daily support in the form of laughs, comMiseration, enthusiasM, and friendship from the meMbers of the Karl, ToBo, and Donahue Labs. Thank you all for being so Wonderful. In addition, I want to thank the Vaughan Lab for welcoming me into their piko and teaching me so much. I also want to thank the KaPAʻA creW for all of the lessons and for the inspirational Work that you are doing. In addition, thank you to the TRHT ʻOhana for filling my mind with iii compassion, hope, and a neW sense of comMunity. To all the teachers who taught me lessons that fell far outside the scope of required classes but that have been integral to my personal and professional development, thank you so very much. I am also fortunate to have aMazing friends Who have lifted me up and inspired me. I have watched theM become partners, parents, professionals, and most iMportantly, beautiful people, and that has been such a gift. To my best friend of all – Spencer Bates – thank you for filling our home and my life With levity, love, and delicious food. I know this has been a long road for you as well, so thank you for your patience. And to my faMily – you are the reason for all that I do. You have alWays been my biggest fans, defenders, confidants, sounding boards, inspiration, Motivation, and source of joy. There are no sufficient words to express my gratitude. This research and my tiMe in school was funded by the following sources: National Science Foundation Graduate Research Fellowship PrograM (Grant #: 1329626); Hawaiʻi Sea Grant; the UH Mānoa Marine Biology Graduate PrograM (SMall Grants AWard & AchieveMent Scholarship); the UH Mānoa Ecology, Evolution, and Conservation Biology prograM (YoshiMoto Fellowship); the HaWaiʻi Institute of Marine Biology (Lord Scholarship & Castro Scholarship); and the AMerican Museum of Natural History (Lerner-Gray MeMorial Fund). iv ABSTRACT Herbivorous fishes are critical to the function and resilience of coral reefs, but their diets and functional roles can show great variability, even aMong closely related taxa. I assessed the diet specialization of herbivorous reef fishes at multiple scales ranging from an exaMination of diet variation on an individual scale to a Pacific wide analysis of functional homogenization in herbivore asseMblages. Using a Molecular metabarcoding approach, I first identified the algal diets of tWo comMon HaWaiian surgeonfishes, Acanthurus triostegus and A. nigrofuscus, which consume large aMounts of turf algae. Because turf algae are difficult to identify visually, especially in the field, our understanding of the true diet breadth of these species has been limited. A. nigrofuscus exhibited greater diet diversity, more variability betWeen individuals, and less variation betWeen sites than A. triostegus. I then used this saMe metabarcoding approach to exaMine the diets of eight other herbivores and conducted a systeMatic literature revieW of studies exaMining herbivorous reef fish diets. I combined these data to generate a standardized index of diet diversity for herbivorous reef fishes, which indicated that parrotfishes and detritivorous surgeonfishes have more liMited diets, but there is also a range of specialization Within each functional group and taxonomic faMily. I combined the index of diet diversity with fish abundance and trait data to exaMine functional homogenization in herbivore asseMblages throughout the Pacific. Using statistical models, I exaMined the direct and indirect effects of a suite of ecological, biophysical, and anthropogenic drivers on herbivores. Differences in herbivore asseMblage composition betWeen islands, regions, and human population densities Were apparent, but local and indirect effects drive variability in the relationship. This work will assist in reevaluating the functional role of herbivores to guide effective manageMent by exaMining herbivore specialization at scales ranging froM an individual to an asseMblage. v TABLE OF CONTENTS AcknowledgeMents ........................................................................................................................ iii Abstract ........................................................................................................................................... v List of Tables ................................................................................................................................. ix List of Figures ................................................................................................................................. x Chapter 1: Introduction ................................................................................................................... 1 Chapter 2: Metabarcoding as a tool to exaMine cryptic algae in the diets of tWo comMon grazing surgeonfishes, Acanthurus triostegus and A. nigrofuscus ............................................................. 4 Abstract ................................................................................................................................... 4 Introduction ............................................................................................................................. 4 Methods ................................................................................................................................... 6 Results ................................................................................................................................... 10 Discussion ............................................................................................................................. 13 Conclusions ........................................................................................................................... 14 AcknowledgeMents ............................................................................................................... 15 Tables .................................................................................................................................... 16 Figures ................................................................................................................................... 18 Chapter 3: Picky eater or generalist feeder? Comparing diet diversity of herbivorous coral reef fishes in the Pacific ...................................................................................................................... 23 Abstract ................................................................................................................................