University of New Hampshire University of New Hampshire Scholars' Repository Doctoral Dissertations Student Scholarship Fall 2008 Survival strategies of eelgrass in reduced light Caroline A. Ochieng University of New Hampshire, Durham Follow this and additional works at: https://scholars.unh.edu/dissertation Recommended Citation Ochieng, Caroline A., "Survival strategies of eelgrass in reduced light" (2008). Doctoral Dissertations. 447. https://scholars.unh.edu/dissertation/447 This Dissertation is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. SURVIVAL STRATEGIES OF EELGRASS IN REDUCED LIGHT BY CAROLINE A. OCfflENG BSc, Egerton University, Kenya, 1994 MSc, University of London, U.K., 1999 DISSERTATION Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Natural Resources and Environmental Studies September, 2008 UMI Number: 3333524 Copyright 2008 by Ochieng, Caroline A. All rights reserved. INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3333524 Copyright 2008 by ProQuest LLC. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 E. Eisenhower Parkway PO Box 1346 Ann Arbor, Ml 48106-1346 ALL RIGHTS RESERVED ©2008 Caroline A. Ochieng 11 This dissertation has been examined and approved. Dissertation Director, Frederick T. Short, Research Professor of Natural Resources and Marine Science David M. Burdick, Research Associate Professor of Marine Wetland Ecology and Restoration Thomas D. Lee, Associate Professor of Forest Ecology Johan Stapel, Executive Officer, Royal Netherlands Academy of Arts and Sciences Leland S. Jahnke, Professor of Plant Biology Date in DEDICATION This dissertation is dedicated to my grandmother, Lea Okello Omullo, also known as "Mama ma Nyakach", whose faith has influenced my life. IV ACKNOWLEDGEMENTS I am indebted to my advisor, Dr. Fred Short for giving me the chance; for guidance and support through all aspects of my thesis; for spending time writing travel and support letters for Funding and for VISAs that enabled me to hop between Kenya, the Netherlands and the USA. Thank you Cathy and Fred for your invaluable editing that has improved my writing. Cathy, your friendship and hospitality kept me going through New Hampshire's cold winters and more! Funding for this thesis was provided by the New Hampshire Port Authority. Additional support came from two Study Leave Grants to Professor Di Walker, University of Western Australia. A Dissertation-Year-Award from Graduate School, University of New Hampshire (UNH), and tuition waiver from the Department of Natural Resources Department were an additional sources of funding. Travel awards provided by the Center for Marine Biology (CMB) and the Furrington Fund of the University of New Hampshire enabled me to present chapter III of this thesis at the 6th International Seagrass Biology Workshop (ISBW 6) in Townsville, Australia. Support by the Western Indian Marine Science Association (WIOMSA) allowed me to present chapter IV at the ISBW 7 in Zanzibar, Tanzania. WL Delft Hydraulics provided in kind support during my stay in the Netherlands. I would like to thank my doctoral committee: Drs. Fred Short (chair), Dave Burdick, Lee Jahnke, Tom Lee, Johan Stapel for their interest in my research, for offering their time and making invaluable comments on my proposal and my final thesis. v Many hands make work light. I am grateful to the Jackson Estuarine Lab crew without whose help this thesis would not have been completed. Thanks to Dave Rivers, Jeff Gaeckle, Debb Lamson and Dave Shay for help with many diving trips in the Great Bay Estuary. Jeff, I felt safe even amidst the boat drive back to JEL through a foggy, snowy, "white sky" after an aborted dive! Thank you the seagrass-salt marsh lab colleagues: Alyson Eberhardt, Cathy Bozek, Lotte Horn, Dave Rivers, Jeff Gaeckle, Rob Vincent, Nicole Petit, Annie Rueb, Heather Tucker and JEQ for your help, whether it was measuring light or plants, weighing plants, cleaning tanks, holding the PAM, grinding rhizomes, driving or just your company. Thanks to Tom Davis and Di Walker for setting up the mesocosms. Also, thanks to Jamie Wolf (JEL weather station data management), Jonathan Pennock (equipment), Jenn Greene and Holly Abeels (chlorophyll analysis), Ray Grizzle (encouragement), Eric Dugre and Jessica Pearson (data entry), and Heather Talbot (administration). Thank you Alison Magil, Andy Quimette and Eric Hobbie for your help with carbohydrate analyses. I am also grateful for the support of several people at WLDelft Hydraulics, the Netherlands, where I spent over a year during my Ph.D. They include the management of MCM, Jeroen Wijsman, Eric van Velzen, Nicky Villars, Maarten Kuijper, Henk van den Boogard, Arno Nolte, Hans Los and Mindert de Vries. When you live in three continents while doing a Ph. D., you have complicated your life. My friends and church communities in my three homes were invaluable during the five years. Haruka Asahina, thank you for the times we laughed and cried together. John and Caren Osambo, Daniel Brogan, Doug and Beth Brogan, Jennifer Day, Mark Kraines, Seth J. Davis, Kent Min Qiang, Mike and Sandy Unger, Faith vi Githui, Ambele, Elizabeth Owuor, Oliver Okumba, George and Lucy Mwangi, Sven Beer, Jacqui Uku, thank you all for what you meant for me, whether it was through shopping, driving, cooking, listening, washing, offering a couch to lie on or just being there! Ank and Henk de Vries, your readiness to help out with taking care of Mendel, and your moral support during the most difficult winding up period cannot be overemphasized. I specially thank Paul Erftemeijer whose untiring support and love, and mental, emotional and financial sacrifices made the whole Ph.D. process successful. Mendel, thank you for cooperating with mama! Finally, praises to God for the abundant provision, care and good health. vn TABLE OF CONTENTS DEDICATION iv ACKNOWLEDGEMENTS v LIST OF TABLES xii LIST OF FIGURES xiv ABSTRACT xvi CHAPTER PAGE I. GENERAL INTRODUCTION 1 LITERATURE CITED 7 II. REVIEW: LIGHT REDUCTION AND ITS EFFECTS ON EELGRASS .... 12 LIGHT AS A REQUIREMENT AND A LIMITING FACTOR FOR EELGRASS GROWTH 13 Light and eelgrass - an introduction 13 The minimum light requirement concept 14 Approaches to investigating minimum light requirements 16 Minimum light requirements - concluding remarks 30 FACTORS REDUCING LIGHT AVAILABILITY TO EELGRASS 33 The nature of light reduction 33 Natural factors that influence light availability 35 Anthropogenic factors that influence light availability 41 viii Concluding remarks 45 RESPONSES OF EELGRASS TO LIGHT REDUCTION 46 Introduction 46 Physiological responses 47 Growth responses 48 Community structure responses 51 Duration of light reduction and its effect on eelgrass response 52 Storage and mobilization of carbohydrate reserves 54 Timing of light reduction 55 Factors that complicate the effects of light reduction 57 Documented decline and loss of eelgrass due to light reduction ... 59 CONCLUDING REMARKS 63 LITERATURE CITED 67 III. PHOTOSYNTHETIC AND MORPHOLOGICAL RESPONSES OF EELGRASS (ZOSTERA MARINA L.) TO A GRADIENT OF LIGHT CONDITIONS .... 85 ABSTRACT 85 INTRODUCTION 86 MATERIALS AND METHODS 88 Experimental design 88 Fluorescence measurements 89 Plant measurements 92 Statistics 93 RESULTS 94 ix Photosynthetic characteristics 94 Plant characteristics and growth 96 DISCUSSION 97 CONCLUSION 103 LITERATURE CITED 105 IV. SURVIVAL OF ZOSTERA MARINA L. AT THE MAXIMUM DEPTH LIMIT AND THE ROLE OF RECOVERABLE RESERVES 119 ABSTRACT 119 INTRODUCTION 120 MATERIALS AND METHODS 123 Site description 123 Depth gradient 124 Deep edge 124 Light measurements 125 Temperature and salinity 126 Plant material 126 Fluorescence measurements 127 ETR versus irradiance curves 128 Chlorophyll content 129 Sugar reserves 129 Estimating growth from rhizome underground sugars 129 Predicting winter growth 130 Data analysis 131 x RESULTS 131 Light availability 131 Water temperature 132 Salinity 132 Photosynthetic rates 133 Chlorophyll content 135 Morphology and biomass 136 Soluble sugars 142 Recoverable rhizome sugars 143 DISCUSSION 145 LITERATURE CITED 159 V. SUMMARY AND SYNTHESIS 182 Light reduction and eelgrass plasticity 182 Minimum light requirements 183 Eelgrass responses to light reduction 184 Acclimation and timing 186 Winter survival at the deep edge 188 Contribution of carbohydrate reserves 189 Conclusion 190 LITERATURE CITED 191 XI LIST OF TABLES CHAPTER II. Table 2.1. Minimum light requirements of eelgrass (Zostera marina L.) expressed as % of surface irradiance 81 Table 2.2 Overview of literature values for the minimum saturating irradiance (4) of eelgrass 82 Table 2.3 Summary of the daily