Interactions between ecosystem engineering by burrowing sandprawns (Callichirus kraussi) and nutrients: consequences for benthic community structure and ecosystem functioning Welly Qwabe Dissertation Submitted for the degree of Doctor of PhilosophyTown in the Department of Biological Sciences University of Cape Town Cape Supervisor: of Dr Deena Pillay University University of Cape Town, Faculty of Science Department of Biological Sciences Rondebosch, 7701 Cape Town South Africa The copyright of this thesis vests inTown the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes Capeonly. of Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University TABLE OF CONTENT Page Plagiarism declaration………………………………………………………………………………………….…. 1 Acknowledgments………………………………………………………………………………………………….. 2 Abstracts…………………………………………………………………………………………………………………. 4 CHAPTER 1: INTRODUCTION AND LITERATURE REVIEW……………………………….………. 8 1.1 The ecosystem engineering concept……………………………………………………………….… 9 1.2 Development and controversies regarding the concept of ecosystem engineering……………………………………............................................................................ 10 1.3 Ecosystem engineering in intertidal soft-sediment habitats…………………………….… 12 1.4 The burrowing sandprawn Callichirus kraussi: organism of this study………........... 1 6 1.5 Ecosystem engineering and contextual dependencies…………………………………….… 19 1.6 Objectives and outline of this dissertation………………………………………………………… 22 CHAPTER 2: METHODS AND MATERIALS…………………………......................................... 26 2.1 Study site………………………………………………………………………………………………………….. 27 2.2 Field Survey…………………………………………………………..……..…………………………………… 28 2. 3 Sample collection……………………………………………………………………………………………… 30 2.3.1 Water column chlorophyll-a (chl-a)…………….………………………………………. 30 2.3.2 Macrofaunal community structure……………………………………………………… 31 2.3.3 Meiofaunal community structure……………………………………………………….. 32 2.3.4 Benthic chl-a concentrations………………………………………………………………. 33 2.3.5 Sediment particle size…………………………..…………………………..……………….. 33 2.4 Factorial experiment…………………………………………….…………………………………………… 34 2.4.1 Design and set-up………………………………….……………………………………………. 34 2.4.2 Data collection and analyses………………………………………………………………. 39 2.5 Statistical analyses……..…………………….…………………………………………….……….………… 40 2.5.1 Multivariate analysis: survey and experimental study……….……..………… 40 2.5.2 Univariate analysis………………………..…………………………………….……………… 41 2.5.2.1 Survey data…………………………………………………………………………… 41 2.5.2.2 Experimental data……………………………………………………………….. 42 2.6 Methodological consideration…………………………………………………………………………… 43 2.6.1 Cage experiment…………………………………………………………………………………. 43 2.6.2 Modelling approach…….……………………………………………………………………… 45 CHAPTER 3: EFFECTS OF COASTAL UPWELLING ON MEIOFAUNAL COMMUNITIES IN SANDPRAWN DOMINATED SANDFLATS………………………….…………………................. 47 3. Introduction…………………………………………………………………….………………………………….. 48 3.1 Environmental contexts…………………………………………………………………….…………….… 48 3.2 Primary productivity: an important contextual dependence in marine ecosystems…………………………………………………………………………..………………………………… 49 3.3 Coastal upwelling……………………………………………………………………………………….……… 50 3.4 Aims and hypotheses……………………………………………………………………………….………… 56 3.5 RESULTS……………………………………………………………………………..……………………………… 57 3.5.1 Water column chlorophyll–a concentrations………….…..……….……………… 57 3.5.2 Sediment chlorophyll-a concentrations……………………..………………………. 58 3.5.3 Meiofaunal community structure: Overall composition……………..………. 63 3.5.4 Community metrics…………………………..………………………………………………… 63 3.5.5 Meiofaunal morphotypes…………….……………………………………………………… 73 3. 6 DISCUSSION…………………………………………………………………...………………………………… 83 3.6.1 Water column chlorophyll-a concentrations……………………………………….. 83 3.6.2 Sediment chlorophyll-a concentrations………………………………………………. 85 3.6.3 Meiofaunal community structure, diversity metrics and morphotypes: sediment surface and burrow walls……………………………………………………………… 87 3.7 CONCLUSION…………………………………………………………………………………………………….. 90 CHAPTER 4: EFFECTS OF UPWELLING ON MACROFAUNAL COMMUNITIES IN SANDPRAWN DOMINATED SEDIMENTS………………………………………............................ 91 4. Introduction…………….……………………….…………………………………………………………………. 92 4.1 Habitat complexity and ecosystem engineering…………….………………………………….. 92 4.2 Hypotheses……………………………………………………………………………………………………….. 97 4.3 RESULTS……………………………….…………..………………………………………….…..…….………… 98 4.3.1 Macrofaunal community structure: overall composition……………………… 98 4.3.2 Community metrics………………………………………………………………………..…… 9 9 4.3.3 Dominant macrofaunal species……………………………………………………….….. 105 4.3.4. Functional groups………………………………………………………………………..…….. 117 4.4 DISCUSSION………………………………………………………………………………………………….…… 124 4.4.1 Macrofauna: overall community composition, diversity metrics………….. 125 4.4.2 Dominant species…………….…………………………………………………………………. 127 4.4.3 Functional groups……………………………………………………………………..………… 130 4.5 CONCLUSION………………………………………………………………………………………………….…. 132 CHAPTER 5: INTERACTIVE EFFECTS OF SANDPRAWNS AND NUTRIENT ENRICHEMENT ON MEIOFAUNAL COMMUNITY STRUCTURE: AN INTER-TIDAL EXPERIMENTAL APPROACH……………………………………………………………………………………. 134 5.1 Introduction…………………………………………………………………………………………………….… 135 5.2 Sandprawns, disturbance and nutrients…………………………………………………..………. 139 5.3 Hypotheses………………………………………………………………………..……………………………... 140 5.4 RESULTS………………………………………….…………………………………………………….………….. 141 5.4.1 Microalgal biomass (chl-a)………….…………..………………………………….………. 141 5.4.2 Sediment bioturbation……………..………………………………………………………… 143 5.4.3 Meiofaunal community structure: Overall composition………..………….… 145 5.4.3.1 Sediment surface…………………..…………………………………………….. 145 5.4.3.2 Burrow-wall………….…………………..………………………………….……… 145 5.4.3.3 Reference…………………………………………………………………………….. 146 5.4.4 Diversity metrics…………..………………………………………………………………..….. 147 5.4.4.1 Sediment surface ……………………….………………………….….……..…. 147 5.4.4.2 Burrow-wall………………………………………………………………….……… 149 5.4.4.3 Reference ……………………………………………………………….…………… 153 5.4.5 Diversity metrics: overall patterns………….……………………..…………..…….… 1 56 5.4.6 Meiofaunal morphotypes…………………………………….…………………………….. 161 5.4.6.1 Sediment surface…………..……….....………………………………………… 161 5.4.6.2 Burrow-wall………………….……..…………………….………………………… 163 5.4.6.3 Reference……………………………..……………………..………………………. 166 5.4.7 Meiofaunal morphotype: overall patterns…………………………………..……… 166 5.5 DISCUSSION………………………………………………………………………………………..…….………. 174 5.5.1 Benthic microalgal biomass (chl-a)…………………………..…………………………. 174 5.5.2 Meiofaunal community structure: Overall composition, diversity and individual morphotypes……………………..…………..……………………..……………………. 178 5.6 CONCLUSION……………………………………………………………………………………………….……. 183 CHAPTER 6: INTERACTIVE EFFECTS OF SANDPRAWNS AND NUTRIENT ENRICHEMENT ON MACROFAUNAL COMMUNITY STRUCTURE: AN INTER-TIDAL EXPERIMENTAL APPROACH……………………………………………………………………………….… 185 6.1 Introduction…………………………………………………………………………………….………………… 186 6.2 Hypotheses………………………………………………………………………………………….….……..... 190 6.3 RESULTS……………………………..………………………………………………….………….……………… 191 6.3.1 Macrofaunal community structure: Overall composition…………..………… 191 6.3.2 Diversity metrics…………………………………………………………………………………. 194 6.3.3 Dominant species………………………………………………..………………………….….. 199 6.3.4 Functional groups………………………………………..………..………….………………… 207 6.4 DISCUSSION…………………………………………………………....…………….….…………………….... 212 6.4.1 Macrofaunal community structure: Overall composition, diversity metrics and dominant species……………….…………………………………………………….. 212 6.4.2 Limited evidence for grazer reversal hypothesis……………………….…………. 215 6.4.3 Functional groups………………………………………………………………….……………. 219 6.5 CONCLUSION……………………………………………………………………………….……………………. 221 CHAPTER 7: FINAL SUMMATION……………………….……………………………………….………..…. 223 7.1 Conclusion………………………………………..……………………………………………..……. 224 7.2 Field observational study…………………………………………………………….…………. 225 7.3 Field factorial study………………………………………………………………………………... 229 7.4 Perspective of future research……………………………………………………………….. 234 CHAPTER 8: REFERENCES……………………..……………………………………………….……………..… 236 CHAPTER 9: APPENDIX……………………………………………………………………………………………. 283 9.1 Porewater nutrients…………………………………………………………………………………. 284 9.2 Generalised linear models used in this study.…….……………………………………. 284 9.3 Scatterplots……………………………………………………………………………………………. 287 PLAGIARISM DECLARATION ● I understand that plagiarism implies copying other people’s work and that includes their ideas, writings or inventions. I also know that plagiarism does not merely include verbatim copying, but also extensive utilization of another person’s idea without acknowledging them in the form of citation. ● I, Welly Qwabe, hereby declare that this is my own work and effort and that it has not been previously submitted at any institution for the degree of Doctor of Philosophy. This thesis contains no material that has previously been published or written by any other person. Where other sources of information have been utilized, they have been acknowledged by referencing. Name: Welly Qwabe Student: QWBWEL001 Signed: Date: 11 October 2019 University of Cape Town Department of Biological Sciences South Africa 1 ACKNOWLEDGEMENTS This PhD thesis demonstrates to me that through education poverty can be transmuted to success. As a black student from underprivileged rural community, achieving this work indicates to me that it is