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Effects of emergent structure on the abundance and size distribution of Trichoptera in Bay of Plenty hill-country streams A thesis submitted in partial fulfilment of the requirements for the degree of Masters of Science (Research) in Biological Sciences at The University of Waikato by James Cooper 2018 Abstract Restoration of streams is not limited to recreating structural habitat complexity, but also requires recolonisation of biota that had been excluded prior to restoration. Aquatic insects are a key component of a streams ecosystem, but often do not recolonise restored sites at expected rates. It is hypothesised that this is due to a lack of suitable habitat for the oviposition of certain groups, particularly the Trichopteran family Hydrobiosidae which is known to use emergent stones to access the stream bed for oviposition. I investigated associations between Trichoptera groups with different oviposition strategies and emergent structure in the form of boulders in six Bay of Plenty stream sites. I compared abundances and size class distribution of Hydrobiosidae, Conoesucidae and Hydropsychidae at sites with and without emergent boulders. Results from that study suggest that the presence of oviposition structure was not linked to either the abundance or size distribution of Hydrobiosidae within the sites we examined where other factors such as degree of shade, water velocity and substrate size were key determinant of larval abundance. This first suggested that Hydrobiosidae may arrive in sites lacking emergent structure via alternative means. Two potential pathways for the colonisation of Hydrobiosidae in reaches without emergent structure were subsequently identified and investigated: (i) access via the banks or emergent vegetation for oviposition; and/or (ii) Hydrobiosidae drift from upstream areas with suitable oviposition habitat. Page | i A study on longitudinal patterns of Hydrobiosidae drift showed inconclusive results, with no significant changes in drift densities or larval size with distance downstream of emergent structure. A study on the lateral distribution of Hydrobiosidae in a reach lacking emergent structure provided evidence that adults were utilising stream banks to access submerged oviposition habitat with higher numbers of smaller Hydrobiosidae found near the stream edges compared to within the channel. Findings from my study suggest that there should not be any constraints on the recolonisation of Hydrobiosidae within a restored reach as long as: (i) there is suitable oviposition habitat <2km upstream of a restored site; (ii) there is a source population of adults capable of reaching oviposition habitat within the targeted stream; (iii) the water quality is suitable for colonisation; and (iv) instream conditions such as shade, substrate size and water velocities are within the preferred ranges. Page | ii Acknowledgements First and foremost I have to give a huge thank you to my supervisors, Kevin Collier, Richard Storey and Brian Smith for putting up me all this time and supporting me throughout this journey. A special thank you to my parents, Kevin & Claire Cooper, for supporting me both morally and financially these past years and especially to my partner, Celsa Davas, both for the support and also for acting as my field assistant. I love you. A big thank you to my other Field assistant, Ashleigh Pos. Thank you for coming out to one of the hardest field sampling days and giving it your all. This thesis would not have been possible without the support and permission of the land owners; in particular the owners of the farm at the Waimapu stream who allowed me free access whenever it was needed. This thesis was conducted as part of a National Institute of Water and Atmospheric Research (NIWA) study into the habitat bottlenecks which can form barriers to the successful recolonisation of stream insects into restored waterways. Funding was provided in part by the Ministry of Business, Innovation and Employment (MBIE) under the “Habitat bottlenecks for freshwater fauna” project. Contract: C01X1615 Page | iii Contents Chapter 1: General Introduction ............................................................................................... 1 1.1 Thesis aims ........................................................................................................................... 6 1.2 Thesis structure .................................................................................................................... 7 Chapter 2: Study Area ............................................................................................................... 9 2.1 Sampling dates ................................................................................................................... 11 2.2 Geology .............................................................................................................................. 11 2.3 Climate ............................................................................................................................... 12 2.4 Hydrology ........................................................................................................................... 14 2.5 Physiochemical attributes .................................................................................................. 16 2.6 Land use ............................................................................................................................. 17 2.7 Ecology ............................................................................................................................... 18 Chapter 3: Effect of emergent structure on the distribution, abundance and size range of Trichoptera ................................................................................................................ 20 3.1 Introduction ....................................................................................................................... 20 3.2 Site description................................................................................................................... 24 3.3 Methods ............................................................................................................................. 25 3.3.1 Field sampling ........................................................................................... 25 3.3.2 Benthic invertebrate collection and processing ....................................... 26 3.3.3 Statistical analysis ..................................................................................... 27 3.4 Results ................................................................................................................................ 29 3.4.1 Habitat characteristics .............................................................................. 29 3.4.2 Trichoptera Fauna .................................................................................... 31 3.4.3 Taxa densities ........................................................................................... 41 3.4.4 Larval sizes ................................................................................................ 46 3.5 Discussion ........................................................................................................................... 48 3.5.1 Comparison of study areas / study limitations ........................................ 49 3.5.2 Community structure and taxa densities ................................................. 51 3.5.3 Size distribution responses to emergent structure .................................. 57 3.6 Conclusion .......................................................................................................................... 60 Page | iv Chapter 4: Lateral distribution and longitudinal drift of larval Hydrobiosidae in Waimapu Stream. .................................................................................................................... 62 4.1 Introduction ....................................................................................................................... 62 4.2 Methods ............................................................................................................................. 66 4.2.1 Site description ......................................................................................... 66 4.2.2 Lateral distribution sampling .................................................................... 66 4.2.3 Longitudinal drift distribution study ........................................................ 69 4.3 Results ................................................................................................................................ 74 4.3.1 Lateral distribution study ........................................................................