CHARACTERISTICS AND IMPLICATIONS OF BRIEF DURATION HYDRODYNAMIC FORCES IN THE INTERTIDAL ZONE A DISSERTATION SUBMITTED TO THE DEPARTMENT OF BIOLOGY AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Megan Morrison Jensen June 2014 © 2014 by Megan Morrison Jensen. All Rights Reserved. Re-distributed by Stanford University under license with the author. This work is licensed under a Creative Commons Attribution- Noncommercial 3.0 United States License. http://creativecommons.org/licenses/by-nc/3.0/us/ This dissertation is online at: http://purl.stanford.edu/mt991tp5954 ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Mark Denny, Primary Adviser I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Derek Fong I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Stephen Monismith I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. George Somero I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. James Watanabe Approved for the Stanford University Committee on Graduate Studies. Patricia J. Gumport, Vice Provost for Graduate Education This signature page was generated electronically upon submission of this dissertation in electronic format. An original signed hard copy of the signature page is on file in University Archives. iii iv Abstract The hydrodynamic forces produced by breaking waves make the rocky intertidal zone one of the most physical stressful environments on Earth. Although the classical in- line hydrodynamic forces, drag and the acceleration reaction, are well studied and characterized, a third in-line force – the impingement force – may be the largest hydrodynamic force in the intertidal zone. Impingement is characterized by a sharp, transient spike in force at the instant of wave arrival, and very few measurements of it exist. I ask several questions about impingement: what variables affect its magnitude and frequency of occurrence? Most importantly, how do brief hydrodynamic loads of this sort affect intertidal organisms? I measured impingement in the laboratory, using a gravity-driven water cannon to simulate waves and tested which variables affect impingement magnitude. I show that impingement is likely drag, rather than an undescribed hydrodynamic force; it likely occurs due to brief increases in flow velocity at the front of a wave. To assess the frequency and magnitudes of impingement events in the field, I built a custom force transducer to record high- frequency forces in the intertidal zone. My data reveal that impingement events occur in 2-7% of waves in the field, but surprisingly, they are not the largest forces: the average magnitude of impingement events is lower than the average maximum force produced by all recorded waves in this study. This suggests that impingement is not the largest hydrodynamic risk to organisms, and future work measuring flows in the intertidal zone should focus on identifying large transient forces regardless of where they occur in a wave. Using these measurements, I explore the likely effects of brief forces on intertidal organisms in two ways: first, I model a limpet as a mechanical spring-mass-damper system and show that its foot has the capacity to reduce the effective force on the animal. I also predict dislodgment rates of three species of gastropod using the maximum forces recorded in my field study. I find that at my site, snails are very susceptible to wave-induced dislodgment. The chapters comprising this dissertation illustrate the necessity of recording high-frequency flows when studying intertidal hydrodynamics. v vi Acknowledgments This thesis is dedicated to my parents, David and Mary Jensen. It takes a village: I could not have written this dissertation and completed this scientific journey from naval architect to biomechanics Ph.D. without an incredible amount of help from many amazing people along the way. These few pages are not enough to express my gratitude for all who have helped me over the last several years, but I hope that the brief thanks here will suffice in lieu of a second dissertation composed solely of acknowledgments. First and foremost, I would like to thank my advisor, Mark Denny. It is impossible to summarize everything I have learned from Mark, but I will attempt to list a few of the things I’ve valued most about the last few years. Mark’s enthusiasm and curiosity are inspiring and contagious, and I view the world differently now – in the best possible way. Mark’s excitement about learning and his expansive knowledge about an astonishingly broad range of topics make him an incredible mentor, and I feel incredibly fortunate to have had the opportunity to work with him. Mark is always willing to answer questions big or small, and more valuably, teach his students to answer those questions for themselves. And for questions without easy answers, Mark taught me that half the fun is figuring out how to ask the question, and then building something to answer it. Mark gave me the tools to succeed, the room to fail when necessary, and helped shape my projects, questions, and ideas into a dissertation. He taught me to be a scientist, and I cannot thank him enough for that. My thesis committee has been exceptionally helpful and a source of many great ideas for my work. George Somero is one of the kindest, most insightful teachers I’ve ever had the pleasure of working with, and even made me tea during a meeting when a coughing fit broke out. Jim Watanabe’s door is always open, and he is perpetually ready to discuss ideas, limpets, algae, statistics, and education, and I appreciate every one of these topics more after sharing perspectives with him. Derek Fong taught one vii of the best classes I have ever taken, and if I ever find myself teaching, I hope to model my lessons on his. Derek asked incredibly insightful questions which always cut straight to the point, and my thesis is greatly improved for his comments along the way. Stephen Monismith lent his expertise at blending hydrodynamics and biology to my committee, and graciously provided me a home away from Hopkins in Y2E2, which allowed me to get to know some of the wonderful people in the EFML. I’ve been fortunate to share the lab with amazing labmates. I especially want to thank our two postdocs, Luke Miller and Kerry Nichols, for all of their help. They have been incredible role models, and have become great friends as well as coworkers. Nearly every aspect of this thesis was helped in some way by one of them: Luke helped with field work, machining, photographing, coding problems, more field work, and even gave car advice on numerous occasions. Kerry was always supportive, offering figure- making tips, fieldwork help, lab and life advice, and a friendly ear. My fellow graduate students, Tom Hata, Diana LaScala-Gruenewald, and Paul Leary, have all helped with field work, lunch chats, and great ideas, and I thank them for everything they’ve done. Kevin Miklasz and Sarah Tepler made the lab a fun place to work, even (especially) when an escalating prank war got slightly out of hand. Anton Staaf imparted circuitry and machining wisdom that continues to be valuable. I am also grateful to a number of visitors to the lab for their ideas, help, and guidance: talking through ideas with Chris Harley, Josh Madin and Bengt Allen during their tenures in the lab improved my work immensely, as well as made days in the lab even more enjoyable. I would like to thank my cohort: Judit Pungor, Carolyn Tepolt, and Chelsea Wood were an incredible resource and support system over the last five-plus years. I count all three of these women among my close friends, and I cannot thank them enough for their examples of the kind of scientist and friend I want to be. From Boston Legal craft nights with Judit to Say Yes to the Dress and wine nights with Carolyn to weekly breakfasts with Chelsea, I owe these women a tremendous amount of thanks for their help, love, and friendship. I am grateful for all of the meals, editing, practice talk help, viii stress relief, and laughter that they brought into my life. Extra thanks must go to Carolyn for supplying baked goods, wine, a beautiful wedding cake, and for telling me over and over and over, “It’ll be ok. Have a margarita.” At Hopkins, we are extremely fortunate to have an amazing staff, who have helped me in innumerable ways over the years. Captaining the Hopkins ship is Judy Thompson, who has saved me from myself more times than there are pages in this thesis. From every rushed order to question about reimbursements, Judy has solved every logistical problem I’ve ever brought her. In the front office, Doreen Zelles cheerfully re-taught me how to send a fax after every committee meeting, and handled more McMaster- Carr orders than I should admit to placing. More importantly, Doreen always offered a smile and a place to relax and chat.