METABOLIC RATE OF THE GAG GROUPER (Mycteroperca microlepis) IN RELATION TO SWIMMING SPEED, BODY SIZE, AND SEASONAL TEMPERATURE By RICHARD JOSEPH KLINE A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004 Copyright 2004 by Richard Joseph Kline To my parents, Nancy and Ron for providing support and encouragement through all of my journeys (and especially for buying my first aquarium and grouper) To Joe Kuban, my high school ecology teacher, who first introduced me to the science of ecology and the marine environment ACKNOWLEDGMENTS I give thanks to Dr. Debra Murie for the opportunity to work in her lab, and on her boat conducting research on gag in the shallow Gulf of Mexico reefs. Without her extensive support, keen eye for what was feasible, and guidance regarding bioenergetic studies, this work may never have been completed. I thank Dr. Daryl Parkyn for his initial advice on theory and construction of respirometer; and for his generous contributions to my knowledge of fish physiology and metabolism. I thank the members of my committee (Dr. Lauren Chapman and Dr. Bill Lindberg). Dr. Chapman also provided advice on initial experimental design, and added to my knowledge of fish physiology. Dr. Lindberg provided a great foundation of knowledge regarding gag grouper, through the Suwannee Regional Reef System; and extensive insight into the history and ecology of the shallow gulf ecosystem. Three other faculty members who played a role in my research regarding fish physiology and ecology were Dr. Frank Chapman, Dr. Chuck Cichra, and Dr. Ken Portier. Dr. Chapman contributed significantly to my education as a physiologist, and emphasized the importance of basic concepts that are often overlooked. Dr. Cichra’s door was always open. He contributed to my knowledge of ecology and was invaluable for his statistical advice and the value of simple explanations. Dr. Portier helped with iv initial experimental design and generously provided several hours of assistance in the analyses of the data and application of the Proc Mixed procedure. This master’s project would not have been possible without help from many people in regards to gag collection and maintenance, extended loans of testing equipment, construction of the holding facility and respirometer, and help with the experimental design implementation and interpretation. I especially thank all of the wonderful people who made this project possible: Dr. Mike Allen, Dr. Shirley Baker, Liz Berens, Dr. Erin Bledsoe, Mark Butler, Doug Colle, Jackie Debicella, Jon Fajans, Dr. Ruth Francis‐Floyd, Jason Hale, Jon Kao, Stephen Larsen, Eddie Leonard, Doug Marcinek, Dr. Frank Nordlie, Sky Notestein, Pat O’Day, Dr. Ed Phlips, Erin Reardon, Dr. Allen Riggs, and Larry Tolbert. I give special thanks to Mark Hebert at Microelectrodes Inc. (Bedford, NH) for custom‐building and donating the oxygen probe used in this study. Financial support for my graduate assistantship was provided through a variety of sources, but primarily the UF College of Agricultural and Life Sciences, the Department of Fisheries and Aquatic Sciences, and the U.S. Department of Agriculture. I thank them all for providing support. Collections of the many gag used in this study, and the materials for building the respirometer, were supported by research funds provided by Dr. Debra Murie and Dr. Daryl Parkyn; and through an associated project in conjunction with Florida Sea Grant. I also thank the Department of Fisheries and Aquatic Sciences for funding construction of the recirculating seawater system and aquatic facilities used for my grouper research. All gag used in this study were captured under a Scientific Activity License issued by the Florida Fish and Wildlife Conservation Commission. v TABLE OF CONTENTS page ACKNOWLEDGMENTS ............................................................................................................iv LIST OF TABLES....................................................................................................................... viii LIST OF FIGURES........................................................................................................................ix ABSTRACT .................................................................................................................................... x CHAPTER 1 INTRODUCTION ................................................................................................................. 1 Bioenergetics .......................................................................................................................... 2 Respirometry ......................................................................................................................... 5 Gag Grouper ........................................................................................................................ 11 Objectives ............................................................................................................................. 14 2 METHODS ........................................................................................................................... 16 Design of the Blazka Respirometer................................................................................... 16 Collection and Maintenance of Gag ................................................................................. 19 Experimental Protocols ...................................................................................................... 21 Statistical Analysis .............................................................................................................. 25 3 RESULTS .............................................................................................................................. 31 Oxygen Consumption at Temperature and Swimming Speed .................................... 31 Swimming Performance..................................................................................................... 31 Multivariate Model Derivation ......................................................................................... 32 4 DISCUSSION ....................................................................................................................... 39 Comparisons of Aerobic Metabolism and Performance................................................ 39 Metabolic Temperature Compensation ........................................................................... 42 6 Utility of the Models........................................................................................................... 45 Costs Associated with Offshore Movements .......................................................... 46 Costs Associated with Annual Metabolic Rates ..................................................... 49 Factors Affecting Respirometry Studies .......................................................................... 51 General Conclusions........................................................................................................... 53 LIST OF REFERENCES .............................................................................................................. 58 BIOGRAPHICAL SKETCH ....................................................................................................... 65 vii LIST OF TABLES Table page 3‐1 Average gag grouper sizes, oxygen consumption rates, and critical swimming speeds at three acclimation temperatures..................................................................... 38 4‐1 Annual and summer energy expenditure for gag grouper for standard, routine, and maximum aerobic oxygen consumption rates modeled in this study. ............. 57 viii LIST OF FIGURES Figure page 2‐1 Modified‐Blazka respirometer used to measure oxygen consumption of gag grouper............................................................................................................................... 29 2‐2 Mean and range of monthly water temperature in the northeastern Gulf of Mexico during 1996 to 2001, at a depth of 13 m, off the mouth of the Suwannee River ................................................................................................................................... 30 3‐1 Relationship of ln scaled oxygen consumption as a function of swimming speed, and temperature in gag grouper, displaying the non‐uniform effects of warm and cold acclimation temperatures................................................................................ 35 3‐2 Mass‐independent oxygen consumption as an exponential function of swimming speed and mean critical swimming speed (drop lines) for gag grouper at three acclimation temperatures................................................................... 36 3‐3 Effect of acclimation temperature on mass‐independent maximum oxygen consumption metabolic scope and standard oxygen consumption of gag grouper............................................................................................................................... 37 4‐1 Standard oxygen consumption as a function of temperature for gag (this study) compared to spotted seatrout, a metabolic compensator, and sand seatrout, a metabolic conformer (modified from Vetter, 1982). .................................................... 55 4‐2 Predicted daily metabolic expenditure (in kJ and kcal) for a 1.8 kg gag grouper at temperatures encountered in the northeastern Gulf of Mexico................................