AN ABSTRACT OF THE THESIS OF Carol A. Blanchette for the degree of Doctor of Philosophy in Zoology presented on August 29, 1994. Title: The Effects of Biomechanical and Ecological Factors on Population and Community Structure of Wave-exposed, Intertidal Macroalgae Redacted for Privacy Abstract approved: Bruce Abstract approved: Redacted for Privacy Jane Lubchenco I examined the biomechanical factors that influence the sizes of intertidal macroalgae by studying a population of Fucus gardneri at Fogarty Creek Point, OR. I constructed a mathematical model to predict optimal sizes and probabilities of survival for Fucus under conditions of high and low wave exposure. Predicted optimal sizes of Fucus closely matched the mean observed sizes of plants collected from wave-exposed and protected locations. To test this hypothesis in the field, I reciprocally transplanted Fucus between wave-exposed and wave-protected sites and found that the degree of wave exposure did not affect survival, but did influence size. Large Fucus were tattered by waves at exposed sites, and small Fucus grew at protected sites. These results support the hypothesis that wave forces can set mechanical limits to size in Fucus. I experimentally examined the relative influences of wave-induced disturbance, competition and predation on the sea palm, Postelsia palmaeformis and its understory community at a wave-exposed site at Depoe Bay, OR. Postelsia recruitment was affected by seasonal variations in disturbance and was greatest in areas disturbed in winter. Postelsia were most abundant at mid-zone, wave-exposed sites, and their restriction to wave-exposed sites seems to be due both to; 1) the occurrence of predictable winter disturbances at these sites which remove mussels, thereby stimulating sea palm growth from the underlying rock, and 2) high water motion which enhances sea palm growth by increasing nutrient exchange and photosynthesis and preventing desiccation at low tide. Competition, disturbance and grazing were all important factors in structuring the Postelsia understory community. Postelsia were dominant competitors and their holdfasts overgrew low-lying plants which were torn loose with Postelsia when this kelp was dislodged by winter storm surf. In the absence of this predictable, seasonal disturbance, competitive understory species, such as Corallina dominated primary space. Intermediate levels of disturbance allowed for the highest understory species diversity. Limpets played a keystone role by grazing Postelsia, the competitive dominant during most of the year, and maintained high levels of species diversity in the algal understory. The Effects of Biomechanical and Ecological Factors on Population and Community Structure of Wave-exposed, Intertidal Macroalgae by Carol A. Blanchette A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed August 29, 1994 Commencement June 1995 APPROVED: Redacted for Privacy Co-Major Professor, representing Zoo gy Redacted for Privacy Co-M rofessor, representing Zoo ogy Redacted for Privacy Chairper epartment of Zoo ogy Redacted for Privacy Dean of Gradu c oo Date thesis is presented August 29, 1994 Typed by author for Carol A. Blanchette ACKNOWLEDGMENTS In my six years of graduate study at OSU, I had the good fortune of interacting with many outstanding people and this thesis is the result of the contributions (both great and small) of many of these. I am particularly grateful to my advisors, Jane Lubchenco and Bruce Menge, who have been excellent mentors and have greatly enhanced my graduate school experience. Both Jane and Bruce provided constant encouragement, support and invaluable advice, yet always allowed me to think for myself. Bruce also provided me with lots of practical field experience at how to drill, scrape, chisel and paint intertidal rock; how to move mussels, seastars, snails and barnacles; and introduced me to the joy of "Z-sparring". I am also grateful to all the members of my graduate committee: Mark Denny, Doug Derryberry, Stan Gregory and Mark Hixon for their helpful comments and advice. I thank all those individuals who helped me in the early, formative stages of this project. Susan Williams and Paul Gabrielson introduced me to the wonderful world of marine algae at Friday Harbor Labs. Tom Daniel, Mark Patterson, Emily Bell and Mark Denny taught me everything I know about physical biology, biomechanics, and "sophisticated" wave- watching. Annette Olson, Peter van Tame len and Brian Tissot helped me to form ideas and design the experiments for most of this thesis. I thank all the members of the Zoology department that have helped out during this project. Thanks to Dianne Rowe in the Zoology office for helping me with all my paperwork and keeping me out of trouble. Thanks particularly to the fifth floor gang, and my past and present labmates for all their help and camaraderie. Gary Allison, Eric Ber low, Dave Booth, Mark Carr, Bryon Daley, Jeff Harding, Denise Idler, Tony Kaltenberg, Dwayne Meadows, Sergio Navarrete, Karina Nielsen, Annette Olson, Deirdre Roberts, Eric Sanford, Cynthia Trowbridge, Peter van Tame len, and Sally Walker have all helped out in various ways. Jeff Harding helped me to relax and think dearly and was an invaluable help in the field on many occasions. He had a keen eye for big waves which kept me out of danger during my stormy, winter fieldwork. My Fogarty Creek pal, Eric Ber low, kept me company in the field and on the many trips to and from Corvallis. Sergio Navarrete constantly amused me, taught me statistics and a few choice phrases in Spanish. I am extremely grateful to all these individuals who got up early in the morning and endured the often cold, rainy hours of data collection and physical labor at some of my hazardous, wave-exposed sites. I was aided in the field by many OSU undergraduates and several Corvallis High School students during the span of this project: Russ Moursund, Russ Sparks, Bryan Profit, Scott Vanderkooi, Doug Whitmore, Michelle Herb, Matt Koenig, Michael Cabrerra, Tonya Goodwin, Meg Miller and Jared Brubaker. I am also grateful to Lavern Weber for providing lab space and housing at the Hatfield Marine Science Center, and to my Newport friends Mitch Vance, Karl Brookins, and Karen Kreeger, who all helped in the field. I am also very grateful to Betsy Abbott and Alice King for providing priveliged, first-dass access to the Fogarty Creek. Their love of nature and their commitment to conservation is warmly appreciated. I am also very grateful to Dr. Mark Denny the members of his lab at Stanford University's Hopkins Marine Station. Brian Gaylord and Mark Denny helped me develop many of the ideas in Chapter II of this thesis and I thank them and Emily Bell for their help and hospitality on my many trips to Pacific Grove, CA. Thanks to Jeff Harding and Evelyn Harding for the artistic and precise rendering of a maximum wave force meter. Finally I thank my family: my parents Ernest and Elsie for their constant support, and my grandparents Agnes and Tony for letting me spend my childhood with them at the beach, and sparking my early interest in marine biology. This research was funded by a Sigma Xi Grant-in-Aid of Research, a Phycological Society of America Croasdale Fellowship, a Seaspace Fellowship and a Holt Marine Education Fund Grant. Research assistance was also provided by National Science Foundation (OCE 88-11369 and OCE 92-17459 to Bruce Menge) and a Mellon Foundation grant to Jane Lubchenco and Bruce Menge. TABLE OF CONTENTS Chapter I GENERAL INTRODUCTION 1 Chapter II CAN WAVE FORCES LIMIT PLANT SIZES IN THE INTERTIDAL? AN EMPIRICAL TEST OF A BIOMECHANICAL MODEL 5 ABSTRACT 5 INTRODUCTION 8 METHODS 15 RESULTS 28 DISCUSSION 37 TABLES 49 FIGURES 63 Chapter III SEASONAL PATTERNS OF DISTURBANCE AND WAVE EXPOSURE INFLUENCE RECRUITMENT AND GROWTH OF THE SEA PALM, POSTELSIA PALMAEFORMIS 100 ABSTRACT 100 INTRODUCTION 102 METHODS 109 RESULTS 115 DISCUSSION 121 TABLES 134 FIGURES 144 Chapter IV THE RELATIVE IMPORTANCES OF COMPETITION, DISTURBANCE AND PREDATION IN A ROCKY-INTERTIDAL, "KELP FOREST" COMMUNITY 169 ABSTRACT 169 INTRODUCTION 172 METHODS 177 RESULTS 183 DISCUSSION 193 TABLES 208 FIGURES 222 Chapter V GENERAL CONCLUSIONS 259 REFERENCES 262 LIST OF FIGURES Figure Page 11.1 A view of Fogarty Creek Point, OR facing west 64 11.2 Maximum wave force meter 65 11.3 RepresentativeFucus gardneri specimens collected from the wave-protected area (P) and the wave-exposed area (E) 66 11.4 A typical wave-protected Fucus transplant showing the marine epoxy /rock adhesion and numbered plastic label 67 11.5 Mean sizes of Fucus gardneri at Fogarty Creek Point, OR at wave- exposed (solid bars) and wave-protected (stippled bars) sites ± 1 s.e.m. in March 1992, August 1992 and February 1993 68 11.6 Mean breaking strengths of Fucus gardneri at Fogarty Creek Point, OR at wave exposed (solid bars) and wave-protected (stippled bars) sites ± 1 s.e.m. in March 1992, August 1992 and February 1993 70 11.7 The probability that a Fucus plant of a given size (planform area) will survive a three month period at either a wave-exposed site where Hm=2 m or a wave-protected site where Hm=1 m, given several levels of acceleration (100-300 m/s2 for the wave- protected site and 500-700 m/s2 for the wave-exposed site) 72 11.8 Index of reproductive output for Fucus plants of various sizes (planform area) for a three month period at either a wave- exposed site where Hm=2 m or a wave-protected site where Hm=1 m given several levels of acceleration (100-300 m/s2 for the wave-protected site and 500-700 m/s2 for the wave-exposed site) 74 11.9 Bars represent mean maximum wave forces (N) recorded at Fogarty Creek Point, OR at both wave-exposed (solid bars) and protected (stippled bars) sites ± 1 s.e.m 76 11.10 Mean and maximum significant wave heights recorded by the NOAA Data Buoy Center from buoy #46040 (44.8° N, 124.3° W).