Wright State University CORE Scholar Browse all Theses and Dissertations Theses and Dissertations 2017 Feeding Selectivity of an Algivore (Tropheus brichardi) in Lake Tanganyika Robin Richardson-Coy Wright State University Follow this and additional works at: https://corescholar.libraries.wright.edu/etd_all Part of the Biology Commons Repository Citation Richardson-Coy, Robin, "Feeding Selectivity of an Algivore (Tropheus brichardi) in Lake Tanganyika" (2017). Browse all Theses and Dissertations. 1710. https://corescholar.libraries.wright.edu/etd_all/1710 This Thesis is brought to you for free and open access by the Theses and Dissertations at CORE Scholar. It has been accepted for inclusion in Browse all Theses and Dissertations by an authorized administrator of CORE Scholar. For more information, please contact [email protected]. FEEDING SELECTIVITY OF AN ALGIVORE (Tropheus brichardi) IN LAKE TANGANYIKA A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science By ROBIN RICHARDSON-COY B.S., Wright State University, 2013 2017 Wright State University WRIGHT STATE UNIVERSITY GRADUATE SCHOOL January 5, 2017 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Robin Richardson-Coy ENTITLED Feeding Selectivity of an Algivore (Tropheus brichardi) in Lake Tanganyika BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science Yvonne Vadeboncoeur, Ph.D. Thesis Director David L. Goldstein, Ph.D. Chair, Department of Biological Sciences Committee on Final Examination James Amon, Ph.D. Volker Bahn, Ph.D. Rebecca Teed, Ph.D. Robert E. W. Fyffe, Ph.D. Vice President for Research and Dean of the Graduate School ABSTRACT Richardson-Coy, Robin. M.S. Department of Biological Sciences, Wright State University, 2017. Feeding Selectivity of an Algivore (Tropheus brichardi) in Lake Tanganyika. Algivorous fish remove attached algae (periphyton) from the benthos in near shore areas of lakes. Periphyton has a complex three-dimensional structure dominated by Bacillariophyta (diatoms), Chlorophyta (green algae), and Cyanophyta (cyanobacteria). These three phyla vary in nutritional quality with diatoms providing essential fatty acids that consumers need for growth and reproduction. Selection of specific phyla may be driven by nutritional quality or it may be a function accessibility due to both mouth morphology of the fish and location of the algae in the periphyton community. I investigated whether Tropheus brichardi, an algivorous cichlid of Lake Tanganyika, selectivity feeds on periphyton and how their herbivory affects the periphyton community composition. I found that T. brichardi slightly selects for diatoms although it is unclear if that selection is driven by nutritional quality or accessibility. This slight selection for diatoms did not appear to affect community composition of the periphyton. iii TABLE OF CONTENTS INTRODUCTION AND OBJECTIVES.........................................................................1 Algal community structure ......................................................................................1 Algivore feeding methods .......................................................................................4 Algal nutritional quality............................................................................................5 Effects of herbivory on community composition.....................................................6 Organism of study, Tropheus brichardi ..................................................................7 Objectives ................................................................................................................7 Hypothesis….……………..……………………………………………………….8 METHODS................................................................................................................... 9 Sample collection ................................................................................................... 9 Fish Denisty............................................................................................................ 9 Algae analysis........................................................................................................ 10 Mounting sample.......................................................................................... 10 Microscopic analysis.................................................................................... 10 Biovolume determination….……………………………………………….11 Data analysis……….……………………………………………………….13 Electivity calculation ……………...……………………………………….13 RESULTS ...................................................................................................................15 Relative abundance………….................................................................................15 Relative biovolume….………..…………………………………………………..16 iv TABLE OF CONTENTS (Continued) Electivity indices………………………………………………………………....17 Diatom relative abundance as a function of fish density……………..………….24 DISCUSSION..............................................................................................................26 CONCLUSION………..…………..…………………………………………………33 APPENDIX A………………………………………………………………………..34 REFERENCES……….………………………………………………………………37 v LIST OF FIGURES Figure Page 1. Community structure of benthic algae….................................................................3 2. Tightly packed fish teeth of T. moorii, a clipper ….…………………….…………5 3. Relative abundance for each phyla on full data set…...…………..……..………16 4. Relative biovolume for each phyla on genus subset samples …..…………….…17 5. Electivity calculated on relative abundance ….………………………………......18 6. Electivity calculated on biovolume ……..……………………………………….19 7. Relative abundance, excluding greens …….…..…………………………………21 8. Relative biovolume, excluding greens……….…………………………………..22 9. Electivity on relative abundance, excluding greens ……………………………23 10. Electivity on biovolume, excluding greens ………………………………………24 11. Relative abundance of diatoms as a function of fish density …….…………….. 25 12. Microscope field with large greens ……………………………….……………..27 13. Stalked Rhopalodia ……………………………………………….……………..31 vi LIST OF TABLES Table Page 1. Biovolume calculations ……………..…...............................................................12 2. Mean values by cell count ……………………………………….………………20 3. Mean values by biovolume ………………………...……………………………20 Appendix Table A1. Relative abundance by count on full data set...…..……….……….…………... 34 A2. Relative biovolume on genus subset samples …….…..….………………..……34 A3. Relative biovolume on genus subset samples ………..…..…..…………………35 A4. Electivity on relative abundance on full data set ………….…………………..35 A5. Electivity on relative abundance on genus subset ………..….…………………36 A6. Electivity on biovolume on genus subset ………………….………..………….36 LIST OF EQUATIONS 1. Example biovolume calculation………..………………………………………...11 2. Alpha selectivity calculation…………………………………………………..…13 vii ACKNOWLEDGMENT I would like to thank my advisor, Dr. Yvonne Vadeboncoeur, for her patience, instruction, and support while guiding my research. I would like to thank Dr. Jim Amon, Dr. Volker Bahn, and Dr. Rebecca Teed for their service on my committee. Further thanks go to Dr. Renalda Munubi not only for collecting the samples and some of the data used in this research but also for her support, encouragement, and advice throughout this project. Thank you also to Dr. Rex Lowe, Dr. Paula Furey, and Leon Katona for assistance in identifying algal species that were particularly challenging. Thank you also to graduate students Hannah Fazekas and Mandy Salminen for their assistance and support on several aspects of this research. Lastly, I’d like to thank my husband, Gary Coy, and my many friends who have helped and encouraged me along the way. viii INTRODUCTION Herbivores reduce the absolute abundance of primary producers by removing biomass (Hairston et al. 1960, Ripple & Beschta 2012). Grazing also alters the proportions of species within the plant community, especially if grazers selectively feed on some species of primary producers (Ripple & Beschta 2012, Hillebrand 2003). Selectivity may be driven by morphological constraints of the consumer (Takamura 1984) or by nutritional quality of the primary producer (Liess et al. 2012, Larson et al. 2013). In aquatic ecosystems, selective grazing by algivores can alter the 3-dimensional structure of the micro-algal assemblage that grows on any surface that receives sufficient light for photosynthesis. We studied the selectivity of an algivorous fish and the effects of that top-down control on the algal community composition in the benthic near-shore area of oligotrophic Lake Tanganyika, East Africa. Freshwater benthic algal communities are primarily composed of three major phyla: Cyanobacteria, Chlorophyta (green algae) and Bacillariophyta (diatoms). These algae have diverse morphological structures and modes of attachment to the benthos. Benthic filamentous cyanobacteria such as those in the family Rivulariaceae form clumps or tufts, with individual filaments attached to the substrate via a basal heterocyte (Bellinger & Sigee 2008). Masses of filamentous cyanobacteria formed from genera in the family of Oscillatoriaceae are motile, so filaments can alternate between laying prostrate on the substrate or protruding vertically to control the amount of light they are 1 receiving (Fogg 2012). Small spherical cyanobacteria, both unicellular and colonial taxa, can be attached to directly