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The Pennsylvania State University The Graduate School Intercollege Graduate Degree Program in Ecology THE INFLUENCE OF HABITAT-MODIFYING FAUNA ON THE COMMUNITY ECOLOGY AT DEEP COLD-SEEPS IN THE GULF OF MEXICO A Dissertation in Ecology by Stephanie A. Lessard-Pilon © 2010 Stephanie A. Lessard-Pilon Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy December 2010 The dissertation of Stephanie A. Lessard-Pilon was reviewed and approved* by the following: Charles R. Fisher Professor of Biology Dissertation Advisor Chair of Committee Iliana Baums Assistant Professor of Biology Denice Wardrop Associate Professor of Ecology and Geography Alexander Klippel Assistant Professor of Geographical Information Sciences David Eissenstat Professor of Woody Plant Physiology Chair of the Intercollege Graduate Degree Program in Ecology *Signatures are on file in the Graduate School ii ABSTRACT Cold seeps commonly occur on continental margins worldwide where hydrocarbons and reduced chemicals emerge from the seafloor. In the Gulf of Mexico, habitat-modifying fauna frequently dominate cold seep communities. Examples of these fauna include large aggregations of mussels and tubeworms as well as mobile animals such as burrowing spatangoid urchins. As seepage declines, cold-water corals settle on authigenic carbonate rock and eventually form large, long-lasting coral reefs that support diverse coral-associated fauna. In this dissertation, physical collections and non- destructive sampling tools such as image and GIS analyses were used to characterize newly discovered cold seep and coral communities as well as examine the mechanisms that influence the ecology of deep seeps. Chapters 2 and 3 examine interspecific interactions and habitat provision and modification by different foundation fauna, such as tubeworms, mussels and corals, which harbor unique communities. These fauna are long-lived, and have generally predictable successional trends that are similar to shallower seeps in the Gulf of Mexico. However, I also show that exceptions to these trends occur when small changes in seepage expression over time influence the recruitment and growth of the foundation fauna. In Chapter 4, I characterize a newly discovered type of seep community dominated by spatangoid urchins (Sarsiaster griegii), and provide evidence for the role of interspecific interactions as a strong influence on the community ecology of seep sediment infauna. I demonstrate that urchins act as habitat- modifying fauna whose activities influence sediment infauna community composition and structure, and contribute to high spatial heterogeneity in deep seep sediments. In these seep communities, the dominant megafauna influence the composition, structure, iii abundance and diversity of the associated community as a result of their physical structure, which provides a habitat resource and as a result of their activities. Facilitative interspecific interactions, particularly between habitat-modifying fauna and their associated communities, strongly contribute to the general patterns in the community ecology observed in these seep environments. iv TABLE OF CONTENTS LIST OF FIGURES ___________________________________________________ vii LIST OF TABLES _____________________________________________________ xi ACKNOWLEDGMENTS ______________________________________________ xiii CHAPTER 1: Introduction and a Review of Gulf of Mexico Oceanography and Cold Seep Ecology __________________________________________________________ 1 Gulf of Mexico Formation and Geological History__________________________________ 7 Gulf of Mexico Topography and Geology_________________________________________ 9 Physical Oceanography and the Gulf of Mexico ___________________________________ 12 Currents _______________________________________________________________________ 12 Depth Gradients _________________________________________________________________ 16 Biological Oceanography and Diversity _________________________________________ 20 General Background Regarding Cold Seep Communities____________________________ 22 Dominant Fauna at Seeps in the Gulf of Mexico___________________________________ 28 Clams _________________________________________________________________________ 28 Mussels _______________________________________________________________________ 29 Tubeworms ____________________________________________________________________ 30 References ________________________________________________________________ 31 CHAPTER 2: Megafauna community composition associated with L. pertusa colonies in the Gulf of Mexico ___________________________________________________ 40 Abstract __________________________________________________________________ 40 Introduction _______________________________________________________________ 41 Methods __________________________________________________________________ 42 Site descriptions_________________________________________________________________ 42 Image collection and analysis ______________________________________________________ 44 Statistical analysis _______________________________________________________________ 46 Results ___________________________________________________________________ 47 Diversity and colonization trends ___________________________________________________ 47 Within-region analyses ___________________________________________________________ 48 Within-site analyses______________________________________________________________ 49 Discussion ________________________________________________________________ 50 Acknowledgments __________________________________________________________ 54 References ________________________________________________________________ 55 Tables and Figures __________________________________________________________ 59 CHAPTER 3: Community composition and temporal change at deep Gulf of Mexico cold seeps ____________________________________________________________ 67 Abstract __________________________________________________________________ 67 Introduction _______________________________________________________________ 68 v Methods __________________________________________________________________ 71 Site descriptions_________________________________________________________________ 71 Image collection and analysis ______________________________________________________ 72 Physical faunal collections_________________________________________________________ 74 Statistical analyses _______________________________________________________________ 75 Results and discussion _______________________________________________________ 75 Community compositions across sites ________________________________________________ 75 Physical faunal collections_________________________________________________________ 79 Temporal change ________________________________________________________________ 82 Acknowledgments __________________________________________________________ 88 References ________________________________________________________________ 89 Figures and tables___________________________________________________________ 95 CHAPTER 4: Urchin bioturbation mediates sediment infauna ecology in deep Gulf of Mexico seep sediments _________________________________________________ 107 Abstract _________________________________________________________________ 107 Introduction ______________________________________________________________ 108 Methods _________________________________________________________________ 111 Characterization of urchin aggregations: urchin movement and associated fauna______________ 111 Urchin collection and stable isotope analysis _________________________________________ 112 Sediment infauna _______________________________________________________________ 113 Statistical analyses and ecological indices____________________________________________ 115 Results __________________________________________________________________ 118 General characteristics of urchin aggregations ________________________________________ 118 Urchin influence on infaunal density ________________________________________________ 120 Urchin influence on community composition and richness _______________________________ 121 Urchin influence on infaunal diversity_______________________________________________ 124 Influence of an artificial urchin on sediment infaunal community density, composition, and richness _____________________________________________________________________________ 125 Discussion _______________________________________________________________ 126 Acknowledgments _________________________________________________________ 134 References _______________________________________________________________ 135 Figures and tables__________________________________________________________ 142 CHAPTER 5: Conclusion ______________________________________________ 173 References _______________________________________________________________ 182 APPENDIX A: Photomosaics and digitizations for Chapter 2__________________ 185 APPENDIX B: Photomosaics and digitizations for Chapter 3__________________ 201 vi LIST OF FIGURES Figure 1.1 Simplified diagram of Gulf of Mexico salt tectonic geology (courtesy of NOAA Ocean Explorer) ............................................................................................. 8 Figure 1.2. a) The major geological features of the entire Gulf of Mexico (from Bouma and Roberts, 1990) and b) bathymetry, regions and lease blocks on the Texas- Louisana continental shelf

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