THE EFFECTS OF ELEVATED TEMPERATURES ON GUMBOOT CHITON (CRYPTOCHITON STELLERI) GRAZING PERFORMANCE AND THERMOREGULATION EFFICIENCY By Lily Clare McIntire A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment of the Requirements for the Degree Master of Science in Biology Committee Membership Dr. Paul E. Bourdeau, Committee Chair Dr. Bengt J. Allen, Committee Member Dr. Erik S. Jules, Committee Member Dr. Frank J. Shaughnessy, Committee Member Dr. Erik S. Jules, Graduate Coordinator December 2019 ABSTRACT THE EFFECTS OF ELEVATED TEMPERATURES ON GUMBOOT CHITON (CRYPTOCHITON STELLERI) GRAZING PERFORMANCE AND THERMOREGULATION EFFICIENCY Lily McIntire Rocky intertidal zones are some of the most thermally stressful environments on earth, where ectotherms deal with tidal fluctuations in air and water temperatures that can exceed thermal performance limits. However, not all intertidal ectotherms face the same exposure risk. On the northwest coast of the United States, summertime low tides occur during midday, exposing ectotherms to stressful temperatures. In contrast, cooler pre- dawn low tides in southern regions buffer ectotherms from thermal stress. Gumboot chitons (Cryptochiton stelleri) are a thermally sensitive intertidal grazer that range from southern California to Alaska, exposing them to a mosaic of thermal stress. I quantified chiton thermal performance limits in the laboratory, by testing the effects of elevated water and air temperatures on grazing. I also compared the thermoregulation efficiency of chitons from thermally-benign northern California (CA) sites with those from thermally- stressful San Juan Island (SJI), Washington sites using three components: 1) biomimetic thermal models deployed intertidally at three sites each in CA and SJI; 2) chiton body temperatures in the field; and 3) chiton thermal preference in a laboratory-based thermal gradient. I found that chiton thermal performance was reduced at 18℃ in water and ii reached their thermal performance limit at 20℃ in air, confirming previous work documenting thermal performance limits on gumboot chiton respiration. I also found that preferred temperatures of chitons were close to their thermal performance limits, but that they rarely achieved body temperatures that would maximize their performance in the field. This suggests that chitons are thermoregulating inefficiently with respect to maximizing performance, but instead may be minimizing exposure to detrimental thermal extremes. iii ACKNOWLEDGEMENTS I would like to thank my funding sources: CSU Council on Ocean Affairs, Science & Technology (COAST), the Marine Coastal Sciences Institute (MCSI), Friday Harbor Labs, the Pacific Northwest Shell Club, the Western Society of Malacologists, Malcom Oliphant Graduate Fund, the Brusca family, HSU Master’s Student Grant, and Sigma Xi Grant-in-Aid-of-Research. Thank you to my advisor, Dr. Paul Bourdeau, for always being supportive and pushing me to become a better scientist and person. He not only helped with developing my project and writing my thesis, he was also an invaluable help in the field and the laboratory, even if it meant installing loggers in the pouring rain. He gave up countless hours and sleep to help me complete this project and I am grateful for every edit and meeting. I would like to acknowledge my committee members for their help and feedback on my thesis. I would also like to thank all of my research assistants who helped in lab and came out into the field at 3 am for multiple days in a row and helped install loggers, take temperatures, and carry heavy buckets full of algae and gumboots. There are too many to name, but I would like to thank Melanie Dominguez, Crystal Hofer, Agustina Marroquin Martinez, and Viki Heller as they were the most consistent helpers that were with me since the beginning. iv All of my lab mates: Jessica Gravelle, Torre Flagor, Wesley Hull, Andrea Fieber, Johnny Roche, Angela Jones, Timothy McClure, and Kindall Murie, thank you for all the helpful feedback on presentations and help in the field and lab. I would like to thank Kindall, not only for helping me with field installs and lab work but being an ever- supportive roommate and friend without whom I would not have made it through graduate school. Jess also was a huge emotional support throughout this process. I could not have built my thermal gradient without Lewis McCrigler and Colin Wingfield in Environmental Engineering drilling holes through the aluminum and Kyle Weis helping me design and build it. I would like to thank Mike Nishizaki for lending me his thermal imaging camera while I was at Friday Harbor Labs. I would like to thank the director and staff (Grant Eberle and Kyle Weis) at the Telonicher Marine Lab for giving me the space and materials to carry out my laboratory experiments. In addition, I would like to thank the director and staff at Friday Harbor Labs for hosting me while I did my research on San Juan Island. Thanks to all the office managers, Yvonne Kugies, Stephanie Stephen, and Liz Weaver for helping me with paperwork and moral support. Finally, I would like to thank my family, my parents, and sisters, Meagan and Ella, my best friend, Tatiana Kotas, and my countless other friends who encouraged and supported me through this process even from Colorado, Kentucky, Florida, and San Diego, and often became unwitting field assistants. v TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii ACKNOWLEDGEMENTS ............................................................................................... iv LIST OF TABLES ............................................................................................................ vii LIST OF FIGURES ......................................................................................................... viii CHAPTER 1: THE EFFECTS OF ELEVATED TEMPERATURES ON GUMBOOT CHITON GRAZING PERFORMANCE ............................................................................ 1 INTRODUCTION .............................................................................................................. 1 MATERIALS AND METHODS ........................................................................................ 5 Effects of water and air temperature on gumboot chiton grazing performance ............. 5 Effects of air and water temperature on macroalgal palatability .................................... 9 Quantifying frequency of exposure to thermal extremes .............................................. 11 Statistical analyses ........................................................................................................ 13 RESULTS ......................................................................................................................... 15 DISCUSSION ................................................................................................................... 20 CHAPTER 2: GEOGRAPHIC VARIATION IN GUMBOOT CHITON THERMOREGULATION EFFICIENCY ........................................................................ 25 INTRODUCTION ............................................................................................................ 25 METHODS ....................................................................................................................... 29 Statistical analyses ........................................................................................................ 36 RESULTS ......................................................................................................................... 37 DISCUSSION ................................................................................................................... 43 LITERATURE CITED ..................................................................................................... 50 vi LIST OF TABLES Table 1. Results from the Games-Howell post hoc test for water temperature effects on gumboot chiton (Cryptochiton stelleri) grazing rates. ...................................................... 16 Table 2. Results from the Mann-Whitney U post hoc tests for air temperature effects on gumboot chiton (Cryptochiton stelleri) grazing rates. ...................................................... 17 Table 3. The aerial thermal limits of intertidal organisms in the eastern north Pacific. ... 24 Table 4. Set of variables that were used to calculate thermoregulation efficiency (E) of gumboot chitons (Cryptochiton stelleri). .......................................................................... 30 Table 5. Results from the post-hoc Tukey HSD Test comparing the Tb’s of gumboot chitons (Cryptochiton stelleri) in different habitats between SJI, WA (SJI) and CA (CA). Bold values indicate statistically significant differences at = 0.10. .............................. 41 vii LIST OF FIGURES Figure 1. Map of northern California field sites where “roboboots” were installed during summer 2019. Baker Beach (41° 2'57.37"N, 124° 7'40.54"W), Devil’s Gate (40°23'55.50"N, 124°22'53.72"W), Belinda Point (39°23'56.5"N, 123°49'10.1"W). ........ 6 Figure 2. (a) A live chiton (left) next to a “roboboot”, pre-installation, in the field. (b) The temperatures of “roboboots” (red line, n = 5) and live chitons (black line, n = 5) taken every 20 minutes over the course of 6 hours. Chitons and roboboots were left in air until they reached 30℃, then placed in flow-through sea tables to quantify how both warmed