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Lottia Gigantea Size and Density Differences in Rocky Intertidal Communities Near Monterey Bay, California

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Lottia Gigantea Size and Density Differences in Rocky Intertidal Communities Near Monterey Bay, California California State University, Monterey Bay Digital Commons @ CSUMB SNS Master's Theses School of Natural Sciences Spring 2011 Lottia Gigantea Size and Density Differences in Rocky Intertidal Communities near Monterey Bay, California Shae Mitchell California State University, Monterey Bay Follow this and additional works at: https://digitalcommons.csumb.edu/sns_theses Recommended Citation Mitchell, Shae, "Lottia Gigantea Size and Density Differences in Rocky Intertidal Communities near Monterey Bay, California" (2011). SNS Master's Theses. 1. https://digitalcommons.csumb.edu/sns_theses/1 This Master's Thesis (Open Access) is brought to you for free and open access by the School of Natural Sciences at Digital Commons @ CSUMB. It has been accepted for inclusion in SNS Master's Theses by an authorized administrator of Digital Commons @ CSUMB. For more information, please contact [email protected]. LOTTIA GIGANTEA SIZE AND DENSITY DIFFERENCES IN ROCKY INTERTIDAL COMMUNITIES NEAR MONTEREY BAY, CALIFORNIA A Thesis Presented to the Faculty ofthe Division ofScience and Environmental Policy California State University Monterey Bay In Partial Fulfillment ofthe Requirements for the Degree Master ofScience In Coastal and Watershed Science and Policy by Shae Mitchell Spring 2011 CALIFORNIA STATE UNIVERSITY MONTEREY BAY The Undersigned Faculty Committee Approves the Thesis of Shae Mitchell: LOTTlA GIGANTEA SIZE AND DENSITY DIFFERENCES IN ROCKY INTERTIDAL COMMUNITIES NEAR MONTEREY BAY, CALIFORNIA Susan Alexander, Chair Division of Science and Environmental Policy Division of Science and Environmental Policy Steve Lonhart Monterey Bay National Marine Sanctuary Marsha Moroh, Dean College of Science, Media Arts, and Technology Approval Date 111 Copyright © 2011 by Shae Mitchell All Rights Reserved iv ABSTRACT Lottia gigantea Size and Density Differences in Rocky Intertidal Communities Near Monterey Bay, California by Shae Mitchell Master of Science in Coastal and Watershed Science and Policy California State University Monterey Bay, 2011 Owl limpets (Lottia gigantea) are ecologically important grazers that live on exposed rocky intertidal shores of the west coast ofNorth America. Lottia gigantea are a major competitor for space and are considered a co-competitive dominant with California mussels (Mytilus californianus) in mid to high rocky intertidal areas from Baja California to Washington. In recent years Lottia gigantea have been impacted by human access via visitation and harvesting. Owl limpet size and density have been correlated with human access, where higher access leads to reduced size and density. Human visitation may have different effects on owl limpets in central California. For instance, human activities may directly and indirectly alter owl limpet population growth via trampling oflimpets and other species. Trampling may also open space in rocky intertidal areas by clearing macroalgae. If space is not a limiting factor in owl limpet populations, then there should be a decrease in intraspecific competition for space, in tum leading to density dependent population growth. The goal ofthis study was to investigate the relationship between humans and their potential impact on owl limpet populations. The underlying objectives were to determine any differences in owl limpet size, density, and species diversity associated with differing levels ofhuman access. Site-level differences ofaccessibility were used to infer how owl limpet density and size distribution have been affected by human access. Sampling was conducted at four sites between Point Lobos, California and southern Monterey Bay, California. Two sites had high human access while the remaining two sites were categorized as having low human access. From July 2009 to September 2010 owl limpets in 10 permanent 1 m2 square plots were counted and measured at each ofthe four sites. Species diversity and visitor use were also measured during the study. A mixed effects model was used to analyze owl limpet size data while a negative binomial general linear model was used to analyze owl limpet density data. Species diversity was calculated from high-resolution digital photos. Contrary to previously published findings, this study found owl limpets were larger and less dense in high access sites and smaller and more dense at low access sites. There was also more open rock and lower species diversity at high access sites. Owl limpets are important ecosystem engineers modifying rocky intertidal habitat, which is an important and rare habitat within Monterey Bay National Marine Sanctuary (MBNMS). Therefore, understanding owl limpet dynamics and human access in MBNMS may assist management and conservation ofrocky intertidal habitats. v TABLE OF CONTENTS PAGE ABSTRACT............................................................................................................................. iv LIST OF TABLES .................................................................................................................. vii LIST OF FIGURES ................................................................................................................ vii ACKNOWLEDGEMENTS ..................................................................................................... ix CHAPTER 1 INTRODUCTION ......................................................................................................... 1 Background ..............................................................................................................1 Historical Human Impacts .......................................................................................2 Current Policies in Monterey Bay........................................................................... .3 Potential Human Impacts in Monterey Bay .............................................................5 Study Objectives ......................................................................................................6 Research Questions ..................................................................................................7 2 METHODS ....................................................................................................................9 Study Site .................................................................................................................9 Sampling Design ....................................................................................................11 Owl Limpet Size and Density ......................................................................... 11 Species Diversity ............................................................................................ 12 Visitor Use ...................................................................................................... 15 Statistical Analysis ................................................................................................. 16 Owl Limpet Size ............................................................................................. 16 Owl Limpet Density ........................................................................................18 Species Diversity ............................................................................................19 Visitor Use ......................................................................................................20 3 RESULTS ....................................................................................................................22 Owl Limpet Size ....................................................................................................22 Owl Limpet Density ...............................................................................................25 Species Diversity ...................................................................................................28 VI Visitor Use .............................................................................................................33 4 DISCUSSION ..............................................................................................................37 Policy Implications ................................................................................................39 REFERENCES ........................................................................................................................43 APPENDICES A COASTAL MARINE ECOSYSTEM SERVICES ......................................................51 B R STATISTICAL COMPUTING CODE ....................................................................58 Vll LIST OF TABLES PAGE Table 1. Study Site Characteristics .......................................................................................... 11 Table 2. Photo Plot Sampling Months .....................................................................................13 Table 3. Estimated Area ofVisitor Observations ....................................................................20 Table 4. Chi-square contingency table with total # ofvisitors ................................................21 Table 5. Summary of Mixed Effects Model, Fixed Effects North Sites ..................................23 Table 6. Summary of Mixed Effects Model, Fixed Effects South Sites ..................................23 Table 7. Summary of Mixed Effects Model, Random Effect North Sites ...............................23 Table 8. Summary of Mixed Effects Model, Random Effect South Sites ...............................23 Table 9. Summary ofNegative Binomial GLM Results, Limpet Density North
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