MICROZOOPLANKTON COMPOSITION AND DYNAMICS IN LAKE ERIE A Thesis Presented to The Graduate Faculty of the University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Kenneth M. Moats May 2006 MICROZOOPLANKTON COMPOSITION AND DYNAMICS IN LAKE ERIE Kenneth M. Moats Thesis Approved: Accepted: ______________________________ ______________________________ Advisor Department Chair Peter J. Lavrentyev Richard L. Londraville ______________________________ ______________________________ Committee Member Dean of the College R. Joel Duff Ronald F. Levant ______________________________ ______________________________ Committee Member Dean of the Graduate School David M. Klarer George R. Newkome ______________________________ Date ii ACKNOWLEDGEMENTS I would like to thank my graduate advisor Dr. Peter Lavrentyev for introducing me to the study of aquatic microbial ecology and for the opportunity to conduct this study. The importance of his guidance and expertise in every aspect of this research cannot be understated. I would also like to thank him for the patience, support, and encouragement he provided throughout my tenure. I would also like to thank the other members of my advisory committee, Dr. Joel Duff and Dr. David Klarer, for the helpful advice and comments offered during the preparation of this manuscript. I would like to extend my thanks to Dr. Klarer and the staff of Old Woman Creek NERR for logistical support and the sharing of unpublished data on Old Woman Creek. I thank Dr. Frank Jochem of Florida International University, Dr. Henry Vanderploeg and Dr. Stuart Ludsin of Great Lakes Environmental Research Laboratory, and the Captain and crew of the US EPA R/V Lake Guardian for logistical support during the Lake Erie experiments. Special thanks to Dr. Francisco Moore for logistical support throughout this study and the National Science Foundation and National Oceanic and Atmospheric Administration for financial support. Finally, I would like to thank my wife and family for the encouragement and support they provided throughout this endeavor. iii TABLE OF CONTENTS Page LIST OF TABLES….…………………………………………………………………….vi LIST OF FIGURES……………………………………………………………………...vii CHAPTER I. INTRODUCTION...........................................................................................................1 II. MATERIALS AND METHODS...................................................................................9 The Study Sites ........................................................................................................... 9 Estuarine Sites………………………………………………………………….9 Offshore Lake Erie Sites……………………………………………………...11 Herbivory Experiments..............................................................................................12 Sample Analysis.........................................................................................................14 Chlorophyll a Analysis………………………………………………………14 Microscopic Analysis........................................................................................15 Phytoplankton Enumeration via Flow-Cytometry............................................16 Phytoplankton Growth and Grazing Mortality .................................................17 III. RESULTS ..................................................................................................................21 Water Temperature...................................................................................................21 Chlorophyll a ...........................................................................................................21 Microzooplankton....................................................................................................22 iv Phytoplankton Growth and Grazing Mortality .................................................................25 Microzooplankton Growth and Production .............................................................26 IV. DISCUSSION............................................................................................................55 Conclusions...............................................................................................................61 REFERENCES ..................................................................................................................62 v LIST OF TABLES Table Page 1 Experimental sites .....................................................................................30 2 Site data…………………………………………………..........................31 3 Distribution of ciliate taxa across estuarine sites……...............................32 4 Distribution of ciliate taxa across offshore sites........................................33 5 Distribution of dinoflagellate and rotifer taxa across estuarine sites….....34 6 Distribution of dinoflagellate and rotifer taxa across offshore sites..........35 7 Microzooplankton biomass........................................................................36 8 Biomass to chlorophyll a ratios…………………….................................40 9 Phytoplankton community growth and mortalilty rates.............................44 10 Phytoplankton growth and mortality rates in size fractions……………...45 11 Phytoplankton mortality rates in dark incubations………………………46 12 Phytoplankton growth and mortality rats based on flow-cytometry…..…47 13 Microzooplankton growth and secondary production……………...……48 14 Average production contribution by microzooplankton groups……...….52 15 Taxon-specific contribution to microzooplankton secondary production………………………………………………………………..53 16 Microzooplankton grazing impact……………………………………….54 vi LIST OF FIGURES Figure Page 1 Sampling locations in Old Woman Creek National Estuarine Research Reserve.......................................................................................19 2 Sampling locations in Lake Erie……………………………………........20 3 Microzooplankton community biomass.....................................................37 4 Relative microzooplankton biomass contribution……………………….38 5 Average total microzooplankton biomass contribution………………….39 6 Total microzooplankton biomass vs. Chl regression for all experimental sites…………………………………………………….…..41 7 Total microzooplankton biomass vs. Chl regression for estuarine experimental sites………………………………………………………...42 8 Total microzooplankton biomass vs. Chl regression for offshore experimental sites………………………………………………………...43 9 Microzooplankton growth vs. phytoplankton mortality dynamic……......49 10 Phytoplankton growth vs. microzooplankton growth dynamics……...….50 11 Phytoplankton growth vs. phytoplankton mortality dynamics….……….51 vii CHAPTER I INTRODUCTION The pelagic microbial food web The Microbial Food Web (MFW) is a complex and dynamic assemblage of planktonic microorganisms including viruses, heterotrophic and photosynthetic bacteria and protists, and micrometazoa (Pomeroy 1974; Azam et al. 1983; Sherr and Sherr 2001). The MFW has been recognized as the dominant creator and processor of primary production in both marine (Sherr and Sherr 2001) and freshwater systems (Fahnenstiel et al. 1998). Constituents of the MFW range in size from 0.02 µm to 200 µm. This range is further divided into size fractions in an effort to describe trophic interactions, although this is not always accurate due to the ability of certain microbial grazers (e.g. dinoflagellates) to ingest prey of similar or greater size (Hansen and Calado 1999). In general terms, the picoplankton (0.2-2µm) size fraction consist mainly of heterotrophic bacteria and autotrophic cyanobacteria (i.e. Synechococcus), although some eukaryotes also fall into this category. The nanoplankton (2-20µm) includes auto- and heterotrophic flagellated protists, smaller diatoms, and some ciliates, whereas diatoms, dinoflagellates, ciliates, and colonial cyanobacteria are major components of the microplankton (20-200µm) size fraction. 1 Plankton are typically assigned the following trophic roles: phytoplankton (algae and cyanobacteria) are primary producers, utilizing photosynthetically active radiation (PAR) to drive CO2 fixation. Heterotrophic bacteria, and grazers are secondary producers due to their dependence on organic material as an energy source. Portions of primary and secondary production are utilized by primary consumers mainly of which are nano-sized flagellates and small ciliates. These grazers are then consumed by microzooplankton- sized ciliates, dinoflagellates, and sarcodines (e.g. heliozoans). Microplankton form a direct trophic link to crustacean mesozooplankton, other planktonic invertebrates, and fish larvae (Stoecker and Capuzzo 1990) as well as benthic invertebrates (e.g. the zebra mussel, Lavrentyev et al. 1995). However, this generalized concept is often difficult to apply within the MFW due to wide spread mixotrophy (i.e. the ability to combine or switch between heterotrophic and autotrophic modes of nutrition, Turner and Roff 1993). In many situations, the MFW includes complex trophic cascades, which have significant effects on the energy transfer through pelagic ecosystems and nutrient cycling rates (Legendre and Rassoulzadegan 1995, Lavrentyev et al. 1997). In freshwater systems, rotifers can act as an additional trophic level within the MFW by feeding on algae, ciliates and other protists (McCormick and Cairns 1991; Weisse and Frahm 2002). These invertebrates (Phylum Rotifera) range in size from 60 µm to 2500 µm and are capable of herbivory, bacterivory, as well as predation on autotrophic and heterotrophic protists (Gilbert