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Macrobenthic Communities in the Northern Gulf of Mexico Hypoxic Zone: Testing the Pearson-Rosenberg Model

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Macrobenthic Communities in the Northern Gulf of Mexico Hypoxic Zone: Testing the Pearson-Rosenberg Model The University of Southern Mississippi The Aquila Digital Community Dissertations Fall 12-1-2015 Macrobenthic Communities in the Northern Gulf of Mexico Hypoxic Zone: Testing the Pearson-Rosenberg Model Shivakumar Shivarudrappa University of Southern Mississippi Follow this and additional works at: https://aquila.usm.edu/dissertations Part of the Biodiversity Commons, Biometry Commons, Environmental Health Commons, Environmental Indicators and Impact Assessment Commons, Environmental Monitoring Commons, Marine Biology Commons, Multivariate Analysis Commons, Oceanography Commons, Population Biology Commons, Terrestrial and Aquatic Ecology Commons, and the Water Resource Management Commons Recommended Citation Shivarudrappa, Shivakumar, "Macrobenthic Communities in the Northern Gulf of Mexico Hypoxic Zone: Testing the Pearson-Rosenberg Model" (2015). Dissertations. 176. https://aquila.usm.edu/dissertations/176 This Dissertation is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Dissertations by an authorized administrator of The Aquila Digital Community. For more information, please contact [email protected]. The University of Southern Mississippi MACROBENTHIC COMMUNITIES IN THE NORTHERN GULF OF MEXICO HYPOXIC ZONE: TESTING THE PEARSON-ROSENBERG MODEL by Shivakumar Shivarudrappa Abstract of a Dissertation Submitted to the Graduate School of The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy December 2015 ABSTRACT MACROBENTHIC COMMUNITIES IN THE NORTHERN GULF OF MEXICO HYPOXIC ZONE: TESTING THE PEARSON-ROSENBERG MODEL by Shivakumar Shivarudrappa December 2015 The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen [DO] ≤ 2 mg/L) on the macrobenthic community on the continental shelf of northern Gulf of Mexico for the first time. The model uses a stress-response relationship between environmental parameters and the macrobenthic community to determine the ecological condition of the benthic habitat. The ecological significance of dissolved oxygen in a benthic habitat is well understood. In addition, the annual recurrence of bottom-water hypoxia on the Louisiana/Texas shelf during summer months is well documented. The P-R model illustrates the decreasing impact of organic enrichment on the macrobenthic community distally from the source. To test the underlying principles of the P-R model using bottom-water concentration of dissolved oxygen as a proxy for distance from the source of organic enrichment, four sites were chosen based on the frequency of hypoxia occurrence in the hypoxic zone of the northern Gulf of Mexico. The chosen sites were arrayed from west to east on the Louisiana continental shelf, where site A was farthest from the Mississippi River and least impacted by seasonal hypoxia with <25% annual exposure time, and site D was closest to the Mississippi River and most impacted by seasonal hypoxia with >75% annual exposure time. Site C was impacted by seasonal hypoxia between 25% and 50% of the time. Site B was impacted by ii seasonal hypoxia between 50% and 75% of the time. Sites B and C were situated near the vicinity of the Atchafalaya River between sites A and D. To measure the spatio-temporal effect of hypoxia on the macrobenthic community, samples were collected during early spring (April 2009), late summer (September 2009), and mid-summer (August 2010). Results indicated that the macrobenthos collected during mid-summer were the most stressed community, with the exception of site C. The cumulative effect of annual hypoxia on the macrobenthos at each site was apparent from the species diversity, abundance, and biomass. High values of species diversity, richness and evenness at site A and low values at site D indicated the existence of a westward-diminishing hypoxic gradient on the Louisiana/Texas shelf interrupted by the Atchafalaya River discharge. Assessment of successional stages of the benthic communities of the four sites with the multivariate analyses of nonmetric multi-dimensional scaling and principal component analysis identified the spatial gradient of hypoxia. Examination of the macrobenthos and available environmental data with canonical correspondence analysis indicated that sedimentary organic carbon, as well as bottom-water dissolved oxygen, had a strong impact on the benthic community structure. The study successfully demonstrated the applicability of the Pearson-Rosenberg model on the Louisiana/Texas continental shelf, and the results were consistent with the predictions of the model. Site A was in the advanced phase of stage II succession; whereas sites B and C were in the intermediate phase of stage II succession, and site D was in the intermediate phase of stage I succession in the Pearson- Rosenberg successional continuum. iii COPYRIGHT BY SHIVAKUMAR SHIVARUDRAPPA 2015 The University of Southern Mississippi MACROBENTHIC COMMUNITIES IN THE NORTHERN GULF OF MEXICO HYPOXIC ZONE: TESTING THE PEARSON-ROSENBERG MODEL by Shivakumar Shivarudrappa A Dissertation Submitted to the Graduate School of The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved: ____________________________________ Dr. Scott P. Milroy, Committee Chair Associate Professor, Marine Science ____________________________________ Dr. Vernon Asper, Committee Member Professor, Marine Science ____________________________________ Dr. Charlotte A. Brunner, Committee Member Professor, Marine Science ____________________________________ Dr. Chester F. Rakocinski, Committee Member Professor, Coastal Sciences ____________________________________ Dr. Kevin Briggs, Committee Member Oceanographer, NOARL & NRL, Stennis Space Center ______________________________________ Dr. Karen S. Coats Dean of the Graduate School December 2015 DEDICATION I would like to thank my parents, friends and family for their continued support and belief. My special thanks to my uncle Mr. Andani Gowda for his vital support. vi ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Scott P. Milroy, and other committee members, Dr. Kevin Briggs, Dr. Charlotte Brunner, Dr. Vernon Asper, and Dr. Chet F. Rakocinski, for their valuable advice and support during the study. I would like to thank the Naval Research Laboratory for funding this project. My special thanks go to Dr. Nancy Rabalais for providing the bottom-water O2 data and to the captain and crew of the R/V Pelican. A special thanks to Valerie Hartmann for spending long hours sorting through samples with me. I would like to extend my thanks to Dr. Karen Orcutt, Dr. Steven Lorenz, and Dr. William (Monty) Graham for briefly serving on my committee during the extent of this study. Special thanks to Dr. Stephan Howden for his help during my first year. I would also like to thank J. Blake, G. Gaston, R. Heard, S. LeCroy, J. McLelland, and D. Menke for providing invaluable taxonomic assistance. I would like to thank G. Cartwright, J. Dale, S. Epps, A. Eubanks, M. Richardson, S.K. Sturdivant, A. Tootle, J. Watkins, and M. Pathare for their help during collection and processing of the data. I would like to thank Dr. Wei Wu for helping me with R-project software and Dr. Donald Redalje for the generous use of his ultramicrobalance. vii TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii ACKNOWLEDGMENTS ................................................................................................ vii LIST OF TABLES .............................................................................................................. x LIST OF ILLUSTRATIONS ........................................................................................... xiii CHAPTER I. INTRODUCTION ............................................................................................ 1 Oxygen and Hypoxia Hypoxia around the World Hypoxia in the Gulf of Mexico Second School of Thought Effects of Hypoxia on Macrobenthos Equilibrium and Pioneering Species Pearson-Rosenberg Model RPD and Vertical Disequilibrium Role of Feeding Guilds in Ecological Succession Ecological Succession Hypotheses and Objectives Overview of Studies Objectives II. METHODS ..................................................................................................... 37 Study Area Experimental Design Sampling Procedure Laboratory Procedure for Benthic Invertebrate Analysis Feeding Guild Diversity Opportunist Species Statistical Data Analysis III. RESULTS ....................................................................................................... 57 General data description Data Distribution Abundance Biomass Estimated Average Individual Biomass Vertical Distribution of Abundance Vertical Distribution of Biomass viii Vertical Distribution of Estimated Average Individual Biomass Shannon Diversity Index (H') Pielou’s Evenness (J) Margalef’s Species Richness Index (SR) Inverse Simpson Diversity Index (1/D) Rarefaction Curves Feeding Guilds: Abundance Feeding Guilds: Biomass Percentage of Opportunist Species Assessment of Species Associations Macrobenthos Species Associations Non-metric Multidimensional Scaling (nMDS) Canonical Correspondence Analysis (CCA) Principal Component Analysis (PCA) Cumulative Hypoxia Effect IV. DISCUSSION ..............................................................................................
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