Positive and negative effects of intertidal algal canopies on fucoid recruitment

Abstract

POSITIVE AND NEGATIVE EFFECTS OF INTERTIDAL ALGAL CANOPIES ON FUCOID RECRUITMENT by Amber I. Szoboszlai Positive and negative factors associated with intertidal algal cover can modify juvenile survival of the fucoid alga Pelvetiopsis limitata. Pelvetiopsis recruits <lcm high were counted monthly in different treatments of dominant algal species for one year in Central California. Density of Pelvetiopsis juveniles varied as a function of algal cover: survival was enhanced at intermediate levels of algal cover, and reduced at very low and high levels. High densities of Pelvetiopsis juveniles and grazers co-occurred, suggesting grazers do not control post-settlement survival. The strong association between the ephemeral alga Porphyra perforata and survival of Pelvetiopsis juveniles emphasized the potential for individual species to structure the system. These relationships suggest that in stressful systems, habitat modification by algae can facilitate algal recruitment by modifying the microhabitat. However, as algal cover increases and physiological stress levels are reduced, the positive effects of algal cover are replaced by negative, competitive interactions among species. ACKNOWLEDGEMENTS The support of my family, my committee, my friends, and the students, staff, and faculty of Moss Landing Marine Laboratories were integral to the completion of this work. Lajos Szoboszlai and my family provided constant support, encouragement, and enthusiasm for my endeavors. Gala Wagner-Haskins, field assistant extraordinaire, was always game for a jaunt to the intertidal. Students in the Phycology lab and the BEERPIGS (Benthic Ecology and Experimental Research, Phycology in General) study group assisted me with field work, project critiques, steady support, and thoughtful guidance of this project from inception to completion. Dr. Michael Graham's infectious enthusiasm for scientific inquiry motivated me to pursue research in the field of seaweed population ecology. Dr. Erika McPhee-Shaw offered great insight on how physical factors may influence seaweed population dynamics. Dr. Diana Steller helped me to understand the entire system, and her suggestions improved the design and presentation of this research. Additional conversations with Michael Foster, David Schiel, Sean Connell, and John Pearse helped to solidify my ideas about the role of intertidal algae in nearshore ecosystems. This project was inspired by my involvement with the National Science Foundation research grant Biodiversity and Ecosystem Functioning in Intertidal Seaweed Communities. This research was supported by funds from San Jose State University (College of Science Dean's Scholarship, Harvey Research Fellowship, Arthur & Karin Nelson Scholarship), Moss Landing Marine Laboratories (Martha Johnston Memorial Scholarship, Departmental Lottery Funds), The Phycological Society of America (Grant in Aid of