Otago Submarine Canyons: Mapping and Macrobenthos Bryce A. Peebles A thesis submitted in partial fulfilment for the degree of Master of Science at the University of Otago December 2013 ii Abstract Submarine canyons are steep-sided “V’ or “U” shaped valleys that incise continental slopes worldwide. The geophysical and oceanographic features of submarine canyons can produce environmental conditions that cause benthic assemblages to be distinctive and productive compared to those of the adjacent slope; however the assemblages are potentially vulnerable to anthropogenic impacts, including bottom fishing. In order to help inform policy and management, submarine canyons need to be objectively defined topographically and their benthic assemblages characterised. A canyon network occurs off the Otago Peninsula, south-eastern New Zealand, but lack of detailed bathymetric data and adequate benthic sampling has limited study of the canyons. This thesis outlines a method of defining submarine canyon areas and examines epifaunal and infaunal assemblages of the Otago canyons and adjacent slope. Objective definition of the Otago canyon network in the GIS software GRASS along with the steps to use this methodology worldwide are described. Archival count data from 1966-74 on the epifauna are analysed using the PRIMER suite of programs to characterise epifaunal assemblages. Anomurans, polychaetes, asteroids and ascidians make up 70% of the epifaunal canyon assemblage. The epifaunal assemblage is clearly defined by water depth and recognisable from 380 m. Quantitative sampling of infauna in Saunders canyon, Papanui canyon and adjacent slope was carried out to examine infaunal community structure of the canyons and adjacent slope. Infaunal canyon assemblages are dominated by polychaetes, amphipods, ophiuroids, decapods and isopods in canyons, accounting for 75% of collected individuals. Polycheates, malacostraceans, ophiuroids and foraminifera comprise the bulk of collected infauna from the slope environment. A checklist of recorded species found in the Otago canyon network is appended. iii Acknowledgements I would like to thank my supervisor, Associate Professor Keith Probert, for his guidance, funding, and undying support and patience he has shown throughout the process of writing this thesis. I also would like to thank Dr. Ashley Rowden for hosting me at NIWA, allowing me to use their bathymetry data, and introducing me to Léo Chaumillon. I am grateful to Léo, Ashley, and Peter Batson for providing the foundation for, and donating their time to discussing aspects of, the GIS work for this thesis. I would like to thank Dave Wilson for constructing the anchor-box dredge used to collect the infauna samples in this study and give thanks to Dave, Keith, Reuben Pooley, Bill Dickson, Phil Heseltine and Bev Dickson for their kindness and help running the operation test of anchor-box dredge. Keith, Bill, and Phil deserve further thanks for their help and support aboard the Polaris II cruise where samples were collected from the Otago canyon network and adjacent slope. I would like to thank Bev, Albert Zhou, and Bob Dagg for their support while working at the Portobello Marine Laboratory. I would like to further thank Bob for his instruction of conducting a grain size analysis. Finally, I would like to thank Geoffrey Smith, Shobhit Eusebius, Robin Andrews, and Dr. Andrew Filmer for emotional support and for keeping me sane through the process of writing the thesis. iv Table of Contents Title Page................................................................................................................................ i Abstract ................................................................................................................................ ii Acknowledgments .............................................................................................................. iii Table of Contents ................................................................................................................ iv Chapter 1 - Introduction ..................................................................................................... 1 The Deep-Sea Environment ............................................................................................... 1 The Environment of the Continental Slope ........................................................................ 3 Geological Aspects of Submarine Canyons ....................................................................... 4 Oceanographical Aspects of Submarine Canyons .............................................................. 7 Benthos of the Slope vs Canyon Environments ................................................................. 8 Submarine Canyons of New Zealand ............................................................................... 11 Benthos of the Otago Canyon Network ............................................................................ 12 Purpose and Intent of Thesis ............................................................................................ 14 Chapter 2 – Defining Submarine Canyons in GIS Software ......................................... 17 Introduction ...................................................................................................................... 17 Methods and Results ......................................................................................................... 20 Generating Elevation, Slope and Features Maps .......................................................... 20 Generating Streams, Basins, and Buffered Maps ......................................................... 25 Combining Slope, Features and Buffered Stream Outputs ........................................... 29 Discussion ......................................................................................................................... 34 Known Deficiencies...................................................................................................... 34 Areas of Further Expansion .......................................................................................... 35 Chapter 3 – Epifaunal Assemblages of the Otago Canyons and Adjacent Slope ........ 37 Introduction ...................................................................................................................... 37 Importance of Benthic Biodiversity.............................................................................. 37 Major Continental Margin Habitats of New Zealand ................................................... 38 Purpose of Analysing Archival Data ............................................................................ 40 Methods ............................................................................................................................ 42 Filtering of Archival Data ............................................................................................. 42 Multivariate Analysis in PRIMER................................................................................ 45 Data ................................................................................................................................... 47 v Results .............................................................................................................................. 47 Discussion ......................................................................................................................... 58 Chapter 4 – Infaunal Macrobenthos of Saunders and Papanui Canyons .................... 66 Introduction ...................................................................................................................... 66 Methods ............................................................................................................................ 69 Sampling Design Testing .............................................................................................. 69 Shipboard Processing of Samples ................................................................................. 71 Sample Sorting.............................................................................................................. 72 Grain-size Analysis ....................................................................................................... 73 Statistical Tests ............................................................................................................. 74 Results .............................................................................................................................. 74 Discussion ......................................................................................................................... 84 Chapter 5 – Conclusion ..................................................................................................... 87 Summary ........................................................................................................................... 87 Objective Definition of Canyons in GIS software ........................................................... 87 Epifaunal Assemblage of the Otago Canyon Network ..................................................... 88 Infaunal Assemblages of the Saunders Canyon, Papanui Canyon, and the Adjacent Slope ..................................................................................................... 89 Areas of Further Study ..................................................................................................... 90 GIS