The zoogeomorphology of case-building caddisfly larvae by Richard Mason A Doctoral thesis submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University (June 2020) © Richard Mason 2020 i Abstract Caddisfly (Trichoptera) are an abundant and widespread aquatic insect group. Caddisfly larvae of most species build cases from silk and fine sediment at some point in their lifecycle. Case- building caddisfly have the potential to modify the distribution and transport of sediment by: 1) altering sediment properties through case construction, and 2) transporting sediment incorporated into cases over the riverbed. This thesis investigates, for the first time, the effects of bioconstruction by case-building caddisfly on fluvial geomorphology. The research was conducted using two flume experiments to understand the mechanisms of caddisfly zoogeomorphology (case construction and transporting sediment), and two field investigations that increase the spatial and temporal scale of the research. Caddisfly cases varied considerably in mass between species (0.001 g - 0.83 g) and grain sizes used (D50 = 0.17 mm - 4 mm). As a community, caddisfly used a wide range of grain-sizes in case construction (0.063 mm – 11 mm), and, on average, the mass of incorporated sediment was 38 g m-2, in a gravel-bed stream. This sediment was aggregated into biogenic particles (cases) which differed in size and shape from their constituent grains. A flume experiment determined that empty cases of some caddisfly species (tubular case-builders; Limnephilidae and Sericostomatidae) were more mobile than their incorporated sediment, but that dome shaped Glossosomatidae cases moved at the same entrainment threshold as their constituent grains, highlighting the importance of case design as a control on caddisfly zoogeomorphology. A second flume experiment found that crawling Glossosomatidae larvae transport sand vertically upwards, from sheltered interstices below gravel particles, onto the surface of armoured gravel-beds, increasing the hydraulic exposure of this sediment. As a result of both larvae crawling and case entrainment, case-building caddisfly were responsible for over 30% of coarse sand transport during low to medium discharge conditions in a gravel-bed stream. Tubular case-builders (especially Limnephilidae) and dome case-builders (Glossosomatidae) were particularly important zoogeomorphic agents, using and transporting substantial amounts of coarse sand and fine gravel. This research has shown that case bioconstruction by caddisfly larvae may have a destabilising effect on sand in gravel-bed rivers. The thesis uses case design to conceptualise and understand caddisfly zoogeomorphology under differing biotic and abiotic controls. Future research should consider sediment stabilisation associated with caddisfly pupation, and the relative importance of destabilisation and stabilisation across spatial and temporal gradients. The broad geographic spread, functional diversity, and commonly high abundances of case-building caddisfly mean that they may have important and widespread implications for sediment dynamics in rivers. ii Acknowledgements Thank you to everybody who has made my PhD experience special. To my supervisors, thank you for this opportunity and for the time and experience you have invested in this project and in me as a researcher. Thank you to Steve Rice, for your enthusiasm which has kept me motivated, your expert guidance, and your dedication to puzzling over the challenges of my PhD. Thank you to Paul Wood, for your humour and care during the stressful times, going above and beyond and offering the practical advice that kept the thesis on track (well nearly!). Thank you to Matt Johnson, for sparking my initial interest in zoogeomorphology and for the help and support which you have provided, during my undergraduate and postgraduate research. Thanks also go to everyone at Loughborough Geography who have made the experience so rewarding. Particular thanks to those who have solved my (many) obscure research obstacles. To Richard Harland who solved most of them, and to Rebecca McKenzie, Daniel Gschwentner and Bailey Stickings for their incredible support with laboratory work. Thank you also to Davide Vettori for lending your flume and hydraulics expertise. Thank you to NERC CENTA for providing the funding for this project and to my CENTA cohort, a fantastic group of fellow PhD students. A huge thank you also to my PhD colleagues. From day one, sitting in the pub at 3 pm because we didn’t know what we supposed to be doing, to today, you have been there for me. Special thanks go to Harry Sanders, for the crazy escapades and injecting into the PhD experience so much enthusiasm. I will never forget eating spaghetti hoops using only a cable tie, whilst sat in the boot of a departmental car in a Scottish layby. Thanks to Ellen Goddard for your support, for the fun times at King Edward Rd. and for help with statistics. Thanks to Keechy Akkerman for the climbing, cats and whisky. Thank you also to a host of other people who have helped with fieldwork or laboratory work; Beth Worley, Ciara Dwyer, Maud van Soest, Tom Stanton, and everyone else who has been an important part of the last 4 years. To my Mum and Dad, thank you for the support over my PhD years and for my initial excitement for the natural environment. Without you patiently waiting for 3-year-old me to stomp through puddles or inspect beetles, I might not have an interest in wildlife and rivers and might have a ‘proper job’ by now! Last, a special thank you to my partner, Hazel Wilson, who has been my rock and inspiration throughout the PhD, here’s to many more adventures! iii Table of contents Abstract ii Acknowledgements iii Table of contents iv List of tables vii List of figures viii Introduction 1 1.1 Research context 1 1.2 Fluvial zoogeomorphology 3 1.3 Invertebrate zoogeomorphology 6 1.3.1 Terrestrial 6 1.3.2 Marine 7 1.3.3 Sediment destabilisation in freshwater habitats: bioturbation and bioerosion 8 1.3.4 Sediment stabilisation in freshwater habitats: bioconstruction and bioprotection 10 1.4 Caddisfly biology and case-building behaviour 12 1.4.1 Caddisfly diversity and life history 12 1.4.2 Caddisfly architecture and bioconstruction 14 1.5 Aim and objectives 17 1.6 Justification of aim and objectives 17 1.7 Thesis structure 20 Chapter 2. A spatial quantification of sediment use by the case building caddisfly community 23 2.1 Introduction 24 2.2 Methods 26 2.2.1 Field sampling 26 2.2.2 Laboratory analysis 27 2.3 Data Analysis 28 2.3.1 Sediment use by individual taxa 28 2.3.2 Sediment use by the whole caddisfly community in a Surber sample 28 2.3.3 Spatial variability in sediment use by the caddisfly community 29 2.3.4 Is caddisfly abundance a control on the mass of sediment used? 29 2.3.5 Relation between sediment availability and sediment use 30 2.4 Results 30 2.4.1 Sediment use by individual caddisfly taxa 30 2.4.2 Sediment use by the whole caddisfly community 30 2.4.3 Spatial variability in community sediment use 36 2.4.4 Relation between abundance and sediment use 36 2.4.5 Relation between sediment availability and sediment use 37 2.5 Discussion 40 2.5.1 Sediment use by individual taxa and the case-building caddisfly community 40 2.5.2 Sediment use by key taxa and potential zoogeomorphological importance 40 2.5.3 Spatial variability in community sediment use and the distribution of case-building caddisfly taxa 41 2.5.4 Sediment use in relation to the abundance of taxa and availability of sediment 42 2.5.5 Methodological discussion 43 2.6 Summary 44 iv Chapter 3. The effect of caddisfly case construction and case design on the entrainment of incorporated sediment. 47 3.1 Introduction 47 3.1.1 Controls on sediment transport 47 3.1.2 Entrainment of caddisfly and the role of the case 48 3.2 Methods 50 3.2.1 Selection of species 50 3.2.2 Flume setup 51 3.2.3 Flume procedure 53 3.3 Data Analysis 55 3.3.1 Hydraulic stages 55 3.3.2 Entrainment 57 3.3.3 Caddisfly case design 58 3.4 Results 61 3.4.1 Entrainment of cases versus constituent sediment 61 3.4.2 Differences in case entrainment between species 63 3.4.3 Differences in constituent sediment entrainment between species 63 3.4.4 The role of case shape for case entrainment 66 3.5 Discussion 67 3.5.1 Transport of caddisfly cases versus sediment (Question 1) 69 3.5.2 Entrainment of loose sediment 70 3.5.3 Movement of cases, role of mass and shape (Question 2) 70 3.5.4 Geomorphological implications of caddisfly case construction 71 3.6 Summary 72 Chapter 4. Vertical sand displacement by Glossosomatidae Agapetus fuscipes larvae 75 4.1 Introduction 75 4.1.1 Sand transport in armoured gravel-bed rivers 75 4.1.2 Context of this Chapter 78 4.2 Methods 79 4.2.1 Flume setup 79 4.2.2 Sediment tray setup 80 4.2.3 Experimental procedure 82 4.2.4 Caddisfly and case analysis 83 4.2.5 Data analysis 84 4.3 Results 85 4.4 Discussion 91 4.4.1 Vertical displacement of sand by Agapetus fuscipes larvae 91 4.4.2 Influence of grain protrusion on sand displacement 92 4.4.3 Influence of flow velocity on sand displacement 93 4.4.4 Combined influence of gravel protrusion and high flow velocity on larvae positioning 93 4.4.5 Zoogeomorphic effects of sand displacement 94 4.5 Summary 96 v Chapter 5. The relative contributions of hydraulics and case-building caddisfly to bedload transport in a gravel-bed stream 98 5.1 Introduction 98 5.2 Methods 100 5.2.1 Field site 100 5.2.2 Pit trap design and deployment 100 5.2.3