Thesis Croel

DOES BIOTURBATION BY THE TADPOLE SHRIMP LEPIDURUS PACKARDI PROMOTE CRUSTACEAN ABUNDANCE AND TAXONOMIC RICHNESS IN CALIFORNIA VERNAL POOLS? A Thesis Presented to the faculty of the Department of Biological Sciences California State University, Sacramento Submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE In Biological Sciences by Russell Croel SPRING 2014 DOES BIOTURBATION BY THE TADPOLE SHRIMP LEPIDURUS PACKARDI PROMOTE CRUSTACEAN ABUNDANCE AND TAXONOMIC RICHNESS IN CALIFORNIA VERNAL POOLS? A Thesis by Russell Croel Approved by: __________________________________, Committee Chair Jamie Kneitel, Ph.D. __________________________________, Second Reader Ronald M. Coleman, Ph.D. __________________________________, Third Reader James W. Baxter, Ph.D. ____________________________ Date ii Student: Russell Croel I certify that this student has met the requirements for format contained in the University format manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for the thesis. _________________________, Graduate Coordinator _________________ Jamie Kneitel, Ph.D. Date Department of Biological Sciences iii Abstract of DOES BIOTURBATION BY THE TADPOLE SHRIMP LEPIDURUS PACKARDI PROMOTE CRUSTACEAN ABUNDANCE AND TAXONOMIC RICHNESS IN CALIFORNIA VERNAL POOLS? by Russell Croel Ecosystem engineers are increasingly recognized for their potential in facilitating habitat restoration efforts. An example of ecosystem engineering in aquatic habitats is bioturbation, the disruption of sediment at the water-sediment interface by animal activity. Among the varying effects they have on aquatic communities, bioturbating animals can facilitate zooplankton recruitment by digging up buried, resting eggs and returning them to the sediment surface, where they have a higher probability of hatching. Such facilitation has been demonstrated in studies involving lake and permanent-pond ecosystems, but the effects of bioturbation in temporary ponds, such as California vernal pools, have largely been overlooked. Vernal pools are home to a strong bioturbator, the endemic notostracan Lepidurus packardi. I hypothesized that bioturbation by L. packardi facilitates the hatching of buried, resting eggs by returning them to the sediment surface. I tested this hypothesis by removing L. packardi from mesocosms filled with natural vernal pool soil and comparing the resulting crustacean communities to those in unmanipulated iv mesocosms. I predicted that mesocosms with fewer L. packardi would have fewer crustacean individuals and/or taxa in the active community, because fewer buried eggs would be returned to the sediment surface. I directly tested L. packardi’s digging abilities by conducting complementary microcosm experiments where I buried propagules (resting eggs and plant seeds) at different depths and added freely roaming or caged L. packardi. These experiments also allowed me to determine whether L. packardi can influence the hatching of resting eggs through kairomones (chemical signals). I found no support for my hypothesis. In the mesocosm experiment, four taxa were actually more abundant, not less, in mesocosms with fewer L. packardi. This indicates that L. packardi was suppressing these taxa in the Control mesocosms, most likely through predation. In the microcosm experiments, I found that L. packardi did not translocate propagules buried ≥ 0.5 cm deep, and that it also consumed eggs (but not seeds) lying on the sediment surface. I further found no evidence for kairomones. Results from the microcosm experiments additionally suggest that i) egg translocation was not masked by egg predation; and ii) propagule translocation simply did not occur. I conclude that bioturbation by L. packardi does not facilitate crustacean recruitment in California vernal pools, and that this taxon influences other crustacean taxa primarily through predation on both resting and active stages. ___________________________, Committee Chair Jamie Kneitel, Ph.D. ___________________________ Date v ACKNOWLEDGEMENTS I thank the outstanding faculty and staff of the Department of Biology for providing me with support and encouragement throughout my academic career at CSUS. I especially thank Dr. Ronald Coleman and Dr. James Baxter for their constructive comments and criticisms of this research. Their guidance and coursework have made me a better scientist, teacher, and writer, and I am grateful that they were on my committee. Dr. Jamie Kneitel, my advisor, deserves singular recognition. He exemplifies what it means to be a great mentor and ecologist. I feel honored to know him and to be part of his scientific pedigree. None of this would have been possible without the unending support of my wife. Not only did she encourage me and provide me with uninterrupted study time over the years, but she also helped me collect data for this project when I was sidelined by a leg injury. In a very literal sense, I could not have completed this project without her. I dedicate this to my father, Philip Miles Croel. vi TABLE OF CONTENTS Page Acknowledgements............................................................................................................ vi List of Tables ...................................................................................................................viii List of Figures.................................................................................................................... ix INTRODUCTION .............................................................................................................. 1 METHODS ......................................................................................................................... 8 Mesocosm Experiment.................................................................................................... 8 Microcosm Experiments ............................................................................................... 15 RESULTS ......................................................................................................................... 21 Mesocosm Experiment.................................................................................................. 21 Microcosm Experiments ............................................................................................... 28 DISCUSSION................................................................................................................... 30 Literature Cited ................................................................................................................. 43 vii LIST OF TABLES Tables Page 1. Summary of crustacean taxa abundance (excluding L. packardi) observed in each treatment group ................................................................................. 22 2. Independent-samples t-test results for evenness, total abundance, and per-taxon abundances in mesocosm experiment.................................................... 25 viii LIST OF FIGURES Figures Page 1. Number of L. packardi captured at each treatment application.................................... 11 2. NMDS ordination of mesocosms.................................................................................. 23 3. Comparison of Bosmina sp., Cypris sp., and Limnocythere ceriotuberosa abundances in Control (unmanipulated) mesocosms vs. mesocosms from which L. packardi was removed weekly..................................... 26 4. ANCOVA comparison of Eucypris sp. abundance in Control (unmanipulated) mesocosms vs. mesocosms from which L. packardi was removed weekly........................................................................................................................... 27 5. Comparison of nauplii and seedling abundances in microcosm experiments .................................................................................................................. 29 ix 1 INTRODUCTION Ecosystem engineers are organisms that modify their physical habitat in ways that affect resource availability to other organisms (Jones et al., 1994). Such habitat modification can promote biodiversity by creating habitat space or ameliorating abiotic stresses. For example, beaver dams can increase habitat complexity in riparian zones, thereby increasing plant species richness (Bartel et al., 2010), and seaweed canopies can reduce thermal and desiccation stresses in intertidal zones, enhancing recruitment and survival of intertidal organisms (Bertness et al., 1999). Because of the positive impacts ecosystem engineers can have on biodiversity, they are increasingly being recognized for their potential in facilitating habitat restoration efforts (Byers et al., 2006). A key goal of habitat restoration is re-establishing biodiversity in ecosystems degraded by human activity (Palmer et al., 1997). An obvious first step in using ecosystem engineers in restoration efforts is identifying engineer species and assessing how their activities affect the community. If an engineer species is found to positively influence the establishment or persistence of other species, its focused use in restoration efforts could contribute to the success of those efforts. For example, lakes that are subject to nutrient loading from human activity can shift from a pristine, clear-water state to a turbid, algae-dominated state. Planting macrophytes in such lakes can facilitate a return to the clear-water state (Byers et al., 2006), in part because macrophytes provide zooplankton, which consume algae, refuge

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