U UNIVERSITY OF CINCINNATI Date: I, , hereby submit this original work as part of the requirements for the degree of: in It is entitled: Student Signature: This work and its defense approved by: Committee Chair: Approval of the electronic document: I have reviewed the Thesis/Dissertation in its final electronic format and certify that it is an accurate copy of the document reviewed and approved by the committee. Committee Chair signature: Environmental Change and Molluscan Death Assemblages: An Assessment of Ecological History Along a Carbonate Bank in Florida Bay A dissertation submitted to the Graduate School of the University of Cincinnati In partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY (Ph.D.) In the Department of Geology Of the McMicken College of Arts and Sciences 2009 by Chad Allen Ferguson B.S. Hope College, 2000 M.S. University of Cincinnati, 2003 Advisor: Dr. Arnold I. Miller Committee Members: Dr. Carlton E. Brett Dr. David L. Meyer Dr. Linda C. Ivany Dr. Richard B. Aronson Abstract Marine death assemblages typically reflect the ecological and environmental signatures of the settings in which they are deposited. Comparatively little is known, however, about the effects of environmental change on death assemblages or with what acuity past changes might be preserved, by proxy, in sedimentary deposits. This study assesses the response of present-day molluscan death assemblages, both among surface sediments and stratigraphically, to an instance of anthropogenic environmental change along a carbonate bank. Additionally, I investigate whether body size changes can be recognized among death assemblages as a component of a broader response to changing environmental conditions. Environmental perturbation along Cross Bank, in Florida Bay, resulted from an experiment, during the early-mid 1980’s, where local benthic environments were subjected to nutrient enrichment. Elevated nutrient levels drove a transition between morphologically and sedimentologically distinct seagrass species, from Thalassia testudinum, the regionally dominant seagrass species, to Halodule wrightii. Altered localities from this previous investigation, occurring at regular intervals along the crest of Cross Bank, were used to form an experimental transect to investigate changes in molluscan death assemblages following environmental changes along the bank. A second, control transect was established at sites approximately 50 m N-NE of altered localities to capture the signature unaltered death assemblages. Data considered here were derived from two distinct sampling protocols: two shallow (~15 cm) push cores and a single (82 cm average length) piston core, later subsampled at 2 cm increments, collected at each of twelve study sites to assess the present state of molluscan death assemblages and their ability to record historical environmental change. i Results demonstrate that molluscan death assemblages can effectively retain, by proxy, evidence of environmental change and signals may persist in the sedimentary record on decadal time scales. A transition from Thalassia to Halodule at altered sites appears to be preserved stratigraphically among death assemblages as an envelope defined by assemblage-level properties and compositional variations, rather than a distinct turnover event. Specimen abundance, taxonomic richness, and calculated evenness display strong declines with depth below the sediment-water interface across study localities, likely a taphonomic modification of assemblages through compaction. Findings also indicate that death assemblages are capable of capturing within-taxon changes in mean body size and distribution over ecological time scales, which may elucidate underlying paleoecological shifts during an environmental change. ii iii Acknowledgements This work was conducted under National Park Serves Permit no. EVER-00225 (accession no. EVER-773) in cooperation with the Everglades National Park and would not have been possible without the generous contribution of time and equipment by G. Lynn Brewster-Wingard and J. Murray of the US Geological Survey, Reston, VA, or assistance in the field by Austin Hendy, J. W. Fourqurean, and D. Szymanski. This work was funded by a grant from Sigma Xi and the University of Cincinnati, through the Department of Geology’s K. E. Caster Memorial Fund and research support from the Graduate Student Governance Association. Support during my graduate studies was provided, in part, by a NASA Exobiology Grant to Arnie Miller. I am most appreciative of the friendship and guidance provided by Arnie Miller, my advisor, who introduced me to taphonomy and actualistic paleoecology, allowed me the freedom to pursue an ambitious dissertation project, and promptly provided valuable feedback on countless drafts of everything from grant proposals to the present document. Arnie advised me during my M.S. at UC and agreed to take me on for a second go-round in the PhD program, which I hope he enjoyed as much as I have. My dissertation committee, including Arnie Miller, Carlton Brett, David Meyer, Linda Ivany, and Rich Aronson, helped me to develop the project and ideas that follow and often served as a vital reality-check on what I might hope to accomplish. These individuals provided invaluable feedback on previous drafts of the three chapters contained in this dissertation and the end product was greatly improved as a result. Valuable assistance with preparation of figures and several statistical analyses was provided by T. Phillips and V. L. Dryfhout, respectively, and Chapter One, which is published in the Journal of Coastal Research, was improved through comments provided by Martin Zuschin and an anonymous reviewer. Leah Robertson and Kevin Bloom spent long hours over the course of two iv summers helping me to process core samples in the ‘Dungeon’ and for that I will be forever grateful. Fellow students at the University of Cincinnati enriched my graduate experience through friendship, by providing thoughtful discussions, and collaborating on research projects. In that vein, I would like particularly thank the following: Alex Bartholomew, James Bonelli, Devin Buick, Kate Bulinski, Sean Cornell, Sarah Derouin, Jason Dortch, Bill Garcia, Katherine Glover, Austin Hendy, Stephanie (Fuentes) Kidwell, Sarah Kolbe, Pat McLaughlan, Scott Myers, Brian and Keri Nicklen, Jocelyn Sessa, Utku Solpuker, Trish Smrecak, Sue Taha-McLaughlan, Andrew Webber, Jackie Wittmer, and Jay Zambito. Sandi Cannell-Duwel and Kate Cosgrove deserve a heartfelt thanks for helping to grease the wheels in and around the department over the years and for making sure everything that was supposed to happen did. I’d like to acknowledge Brian Bodenbender, a former mentor, for introducing me to paleontology and providing early research experience. Karla Parsons-Hubbard and Denny Hubbard loaned me equipment over the years and shared their vast knowledge of all things coring. Finally, I would like to thank my wife, Vicki Dryfhout, for supporting and putting up with me over the years. Vicki moved with me, in 2001, to a strange place called Cincinnati, endured the frequency of my travels, shared experiences as a graduate student, and kept me grounded with her love and friendship along the way. v Preface Marine death assemblages typically record the ecological and environmental signatures of the settings where they are deposited. While many previous researchers have documented the fidelity of death assemblages to the living assemblages from which they were derived, comparatively little is known about the responses of death assemblages to environmental changes: specifically, whether or with what acuity the signatures of environmental changes or perturbations are preserved, given the potential for time-averaging and post-mortem disturbance. Because preservational biases and the lack of living analogues often make fossil assemblages difficult to assess, present-day, accumulating death assemblages serve as natural laboratories to investigate directly the temporal acuity of fossil assemblages. Collectively, the studies included herein as elements of this dissertation focus on the responses of accumulating molluscan death assemblages to ecological and environmental change, and how these changes ultimately get recorded in sedimentary deposits. In this context, I focused here on an empirical, spatio-temporal assessment of molluscan death assemblages associated with a well constrained, anthropogenic environmental change along a carbonate bank in Florida Bay that took place during the early-mid 1980’s. At sites along Cross Bank, in the Everglades National Park, seabirds roosting on a series of locality markers polluted benthic environments with their droppings, elevating sedimentary nutrient levels and inducing a persistent shift in competitive relationships among benthic seagrass species, resulting in a shift in dominance from one seagrass species to another. The effects of this change on molluscan death assemblages and their implications for diagnosing paleoenvironmental proxy signals in deep time and for long-term ecological monitoring in coastal settings are assessed in the three chapters comprising this dissertation.. Broadly, death assemblages are found to reflect environmental vi differentiation between anthropogenically altered and unaltered localities, and these proved useful for determining the stratigraphic position of paleoenvironmental turnover in the sedimentary column, in terms of both assemblage composition and body-size