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Campbell Robertwilliam Phd Overwintering Ecology and Ecophysiology of Neocalanus plumchrus by Robert William Campbell B.Sc., University of Toronto, 1996 M.Sc., Dalhousie University, 1998 A Dissertation Submitted in Partial Fulfillment of the Requirements for the degree of DOCTOR OF PHILOSOPHY in the School of Earth and Ocean Sciences We accept this dissertation as conforming to the required standard Dr. J.F. Q^wer, Sup^t^Q^^^SchdLl of Earth and Ocean Sciences) Dr. IÇiCT^en^n, Departmental Member (School of Earth and Ocean Sciences) ^ ^ _______________________________________________ Dr. DXriVIackas, Departmental Member (School of Earth and Ocean Sciences) Dr. V. Tunnicliffe, Ou(#le Member (Department of Biology) Dr. C.B. Miller, External Examiner (College of Ocean and Atmospheric Sciences, Oregon State University) © Robert William Campbell, 2003 University of Victoria All rights reserved. This dissertation may not be reproduced in whole or in part, by photocopying or other means, without the permission of the author. 11 Supervisor: Dr. John F. Dower ABSTRACT Neocalanus plumchrus is the most common copepod in the Northeast Pacific, and as such plays in important role in the ecosystems of that area. The bulk of N. plumchrus’’ annual life cycle is spent in a dormant overwintering state, and little is known of its ecology, behaviour, or physiology during that period. The goal of this thesis is to describe the physiological changes that occur during the overwintering period, and explain how they interact with the physical environment to produce observed life history patterns. Lipid stores in N. plumchrus were primarily wax esters, and were in highest abundance in overwintering stage 5 copepodids. Consumption of wax ester stores began approximately two months prior to moulting in situ. Rates of lipid use in the in situ population and a number of laboratory incubations ranged from 0.3-1% d ', with 22 - 60% of total wax ester reserves used prior to moulting, presumably to fuel gonadogenesis. Concurrent measurements of protein content and glutamate dehydrogenase activity (an enzyme involved in protein catabolism) did not show any significant protein use during overwintering. Incubation experiments suggest that N. plumchrus has some concept of the time of year (i.e. an endogenous clock), but the use of external cues cannot be ruled out. It is often assumed that the abundant lipids found in calanoid copepods play some role in buoyancy regulation. However, lipids are generally more compressible, and more thermally expansive than seawater, which means that neutral buoyancy will be inherently unstable. A simple model of mass density shows that (i) individuals will only be able to stay at depth if they are able to diagnose where they are neutrally buoyant, and (ii) the buoyancy properties Ill of an individual are extremely sensitive to its chemical composition. In the Strait of Georgia, depth-specific measurements of abundance showed a shift towards deeper depth distributions over the course of the overwintering period. Model results suggest that lipid use could be responsible for those changes, though deep water renewal events that occur regularly in the Strait of Georgia in winter may also have been partially responsible. Dr. J.F^ow er, S^ïperVîsor (School of Earth and Ocean Sciences) Dr. K.L. Denman, Departmental Member (School of Earth and Ocean Sciences) --------- M ---- :---------------------------------------------------------------------------------------- Dr. D.l5r Mackas, Departmental Member (School of Earth and Ocean Sciences) Dr. V. Tunnicliffe, Outaf^e^ember (Department of Biology) Dr. C.B. Miller, External Examiner (College of Ocean and Atmospheric Sciences, Oregon State University) IV TABLE OF CONTENTS ABSTRACT................................................................................................................................ ii TABLE OF CONTENTS.............................................................................................................iv LIST OF TABLES..................................................................................................................... viii LIST OF FIGURES......................................................................................................................ix ACKNOWLEDGMENTS.......................................................................................................... xi DEDICATION.......................................................................................................................... xii CHAPTER I .................................................................................................................................. 1 1.1 General Introduction ................................................................................................. 1 1.2 Dormancy in the copepoda ........................................................................................ 1 1.3 Physical and biological setting in the northeast Pacific ..................................... 3 1.4 Physical and biological setting in the Strait of Georgia ....................................... 5 1.5 Rationale and objectives for this thesis ..................................................................7 1.6 Structure of the thesis.................................................................................................8 CHAPTER 2 The role of lipids in the maintenance of neutral buoyancy by zooplankton .......... 9 2.1 Introduction ................................................................................................................ 9 2.2 Neutral buoyancy by lipids is not stable ..............................................................10 2.3 The role of lipids in buoyancy regulation: A copepod example ......................10 2.3.1 A simple model for mass density ......................................................... 10 2.3.2 Maintenance of overwintering depth ...................................................14 2.3.3 Termination of Overwintering ..............................................................16 2.4 Implications ...............................................................................................................17 2.4.1 The case for a buoyancy control mechanism in copepods ............... 17 2.4.2 Effects in surface w aters ........................................................................ 20 V 2.4.3 Measurements of mass density and aeoustic backscatter .................21 2.5 Conelusions ..............................................................................................................22 CHAPTER 3 Ecophysiology of overwintering in the copepod Neocalanus plumchrus: Lipid contents and stage composition ................................................................................. 24 3.1 Introduction .............................................................................................................. 24 3.2 M ethods .....................................................................................................................26 3.2.1 Collection .................................................................................................26 3.2.2 Incubations .............................................................................................. 28 3.2.3 Lipids ....................................................................................................... 28 3.3 Results .......................................................................................................................30 3.3.1 Strait of G eo rg ia ......................................................................................30 3.3.2 Incubations ...............................................................................................33 3.4 Discussion ................................................................................................................ 35 3.4.1 Lipids ....................................................................................................... 35 3.4.2 Termination of dormancy ...................................................................... 41 CHAPTER 4 Ecophysiology of overwintering in the copepod Neocalanus plumchrus: Enzyme activity and protein content .......................................................................................... 44 4.1 Introduction ..............................................................................................................44 4.2 Methods .....................................................................................................................46 4.2.1 Collection and incubations ....................................................................46 4.2.2 Protein content ........................................................................................47 4.2.3 ETS activity .............................................................................................. 47 4.2.4 GDH Activity ..........................................................................................48 4.2.5 Calibrations ............................................................................................ 49 4.3 R e su lts .......................................................................................................................50 4.3.1 Strait of Georgia population ..................................................................50 4.3.2 Incubations ...............................................................................................53 4.4 Discussion ...............................................................................................................
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