Benthic community structure and environmental drivers on Monowai Seamount, Kermadec volcanic arc Niharika Dutt Long A thesis submitted for the degree of Master of Science At University of Otago, Dunedin, New Zealand 26 June 2014 ABSTRACT Seamounts are spatially isolated, underwater topographical features that extend more than 1 km above the seafloor. They are products of geological processes, and exhibit diverse forms of venting as a result of volcanism due to plate tectonics. Environmental factors vary greatly on seamounts, due to which they support communities of specialist chemosynthetic invertebrates, suspension-feeding fauna, and large mobile megafauna including many commercially-important fish species. In addition to threats from benthic trawling, seamounts are now viewed as repositories for Seafloor Massive Sulphide (SMS) deposits, owing to their venting activity. The seamounts of the 2500 km-long Tonga-Kermadec volcanic arc are diverse in their hydrothermal activity and, therefore, are potentially of mining interest. Species diversity and abundances differ within and between seamounts of the Kermadec volcanic arc, according to prevailing environmental factors. Three abiotic variables (i.e. water depth, substrate type, proximity to vent sites) were chosen in order to examine their effect on taxa richness, abundances, and benthic community structure for the current study on Monowai Seamount, northern Kermadec volcanic arc. Monowai Caldera was explored as part of the 2005 New Zealand-American Pacific Ring of Fire, using the submersible Pisces V. 4500 still images and 16 hours of video footage for three dives were acquired for recording data on substrate type, water depth, proximity to vent sites, taxa abundance, and composition. 166 workable samples were chosen for further analysis after excluding images that lacked clarity. Still images were matched with frame grabs from video footages for acquiring information on water depth, geographical coordinates, and small-scale distances to a vent opening within samples. OFOP (Ocean Floor Observation Protocol) was used for recording seafloor observations and mapping of habitat and associated taxa on to a calibrated map of the caldera. Habitat maps and faunal distribution maps visually represented the spatial distribution of habitats, vent, and non-vent assemblages, along with identification of an area of the caldera that was hydrothermally active in 2005. Multivariate analyses, using PRIMER v.6 with PERMANOVA, distinguished key variables responsible for the variation in i the faunal community structure. Substrate heterogeneity, composition, and associated vent- and non-vent taxa were also identified. Faunal zonation with distance to the nearest vent sample was evident, with the first 300 m from a vent site defined as the vent zone. Univariate statistics, using R and JMP, tested for significant effect of environmental variables on taxa richness and abundance. The predictor variables showed a weak relationship with taxa richness. However, substrate differences and distance to the nearest vent site had a significant effect on taxa abundance. Small-scale examination of distances from a vent opening within samples did not show strong relationships to taxa richness and abundances. Despite a low sample size, an inverse relationship of vent fluid temperatures on taxa abundance was obvious. Further biological explorations are needed to record the spatial and temporal changes on Monowai Caldera. Other baseline studies, similar to the current study, need to be widely undertaken when considering management and conservation strategies for the protection of such vulnerable ecosystems against seafloor mining. ii ACKNOWLEDGEMENTS My interest in seamount ecology was initiated when I met Dr Malcolm Clark (NIWA Wellington) while in my final year as an undergraduate student at Victoria University of Wellington in late 2006. Subsequently, I got in touch with Dr Keith Probert in mid-2007, expressing my interest to pursue a Masters at Otago University. After a hiatus of 4 years, I got in touch with Dr Malcolm Clark again in 2010, who subsequently introduced me to Dr Ashley Rowden (NIWA Wellington). Malcolm and Ashley’s ideas helped me in narrowing down the choice of seamount, available data that were un-analysed at NIWA, and the kind of questions that could be answered with the given data for this project. I would like to thank Keith for being a great supervisor. He has been a great help in my write-up and with returning drafts promptly. Ever the patient listener, he has always been there if I have felt the need to ‘vent’. His guidance, ideas, suggestions, and feedbacks sprinkled with a sense of humour have been very helpful. Ashley has been crucial in steering this project, guiding me with advice on statistical routines and the content of the write-up. He has motivated me whenever I have been at NIWA sitting through hours of often painstaking image analysis. Malcolm has been helpful with providing me with papers, relevant to my subject of study. Thank you to Dr Steve Dawson, Dr Abby Smith, Dr Candida Savage, Dr Steve Wing for providing me with helpful feedback during my MARI495 pilot study which all helped in improving the Masters project, and to Dr Mark Hassall (University of East Anglia) for providing helpful pointers. Thank you to Steve Cutler at the New Zealand Marine Studies Centre for employing me to be a mentor during the year. It was helpful in taking my mind off my research for small periods of time by being involved in school programmes. The methods used in this project would not have been possible without the help and guidance from NIWA image-analysis technicians. Despite their busy work schedules, they have always taken the time to teach me image analysis techniques and how to best work with data. Help was always an email away or a knock away from their office door (when I was working through my samples at NIWA). iii Special thanks to Caroline Chin for teaching me how to render DVDs containing video-footages of the dives on Monowai into usable format, OFOP, and mapping. A big thank you goes to Mark Fenwick and Rob Stewart who helped me with ImageJ, species identifications, and to the NIWA ArcGIS department for providing a bathymetric map of Monowai Caldera. Thank you to Dr Bruce Marshall (Te Papa) and Dr Steve O’ Shea who helped with mollusc and cephalopod identifications respectively. Peter McMillan (NIWA) and Andrew Stewart (Te Papa) helped with fish identifications. Guidance on identifying anemones was provided by Dr Daphne Fautin (University of Kansas). A big thank you to Kendall Gadomski (PhD student) whose assistance in creating the location map of Monowai using ArcGIS was invaluable, Suse Schüller (PhD student) for advice on statistical routines and motivational Yoda quotes, and Álvaro Sepulveda (MSc graduate, Science Communication) for his ideas and feedback on my project. Thanks to my fellow friends in the Department of Marine Science: Ellen Miller, Gaya Gnanalingam, Matt Desmond, Peri Subritzky, and Shaun Cunningham, who have helped with answering small queries from time to time and helped me de-stress when times got tough, through humour and laughter. Thank you to my grandfather, Keshab Dutt for the moral and financial support over the last two years. Lastly, this project would not have been possible without three key people in my life: my husband Daniel, my mother Krishna, and my mother-in-law, Jen. Their constant love, support, encouragement, constructive criticisms, and unbelievable patience kept me motivated through the highs and lows. I would like to thank my late grandmother Rekha Dutt, who sadly passed away on New Year’s Eve 2012 from cancer. She was always thrilled with marine biology, loved the idea of research, and instilled a streak of perseverance and stubbornness in me since I was a little girl. She would have been happy with the outcome of this project, even though, for some reason, she always assumed I was working on fish guts! Christopher Paolini (Eragon): “The sea is emotion incarnate. It loves, hates, and weeps. It defies all attempts to capture it with words and rejects all shackles. No matter what you say about it, there is always that which you can't.” iv TABLE OF CONTENTS Abstract .................................................................................................................................... i Acknowledgements ................................................................................................................ iii Table of contents ..................................................................................................................... v List of tables ......................................................................................................................... viii List of Figures......................................................................................................................... ix 1. INTRODUCTION ............................................................................................................. 1 1.1 Seamounts as a benthic habitat ..................................................................................... 1 1.2 Environmental factors influencing benthic communities on seamounts ...................... 3 1.2.1 Water depth .................................................................................................... 4 1.2.2 Substrate heterogeneity ................................................................................... 7 1.2.3 Hydrothermal