DOES EPIBIOSIS FACILITATE THE INVASION SUCCESS OF MARINE BENTHIC INVERTEBRATES? By Kaeden Leonard (BAppSc Marine Environment (Honours) Submitted in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY In the field of Invasion Ecology Committee in charge: Professor Chad L Hewitt (University of Waikato), Chair Professor Marnie Campbell (University of Waikato) Dr Carmen Primo (University of Tasmania) UNIVERSITY OF TASMANIA January 2015 Declaration of Originality "This thesis contains no material which has been accepted for a degree or diploma by the University or any other institution, except by way of background information and duly acknowledged in the thesis, and to the best of my knowledge and belief no material previously published or written by another person except where due acknowledgement is made in the text of the thesis, nor does the thesis contain any material that infringes copyright.” Authority of Access This thesis may be made available for loan and limited copying and communication in accordance with the Copyright Act 1968. ACKNOWLEDGEMENTS This dissertation represents the culmination of a lengthy journey that could not have been possible without the help, support and patients of many people. I would like to acknowledge the significant role my advisors have played in my professional and personal development during my whole academic endeavour; I am deeply honoured to have had their unparalleled encouragement, guidance, and support. I would like to thank Professor Chad Hewitt for not only encouraging me, but also challenging me to think about my research in different ways; Professor Marnie Campbell for her valuable feedback, insight, unwavering support and guidance throughout this project; and Dr Carmen Primo who has been a friend and a mentor, her invaluable advice and support has made all the difference, I was fortunate to have her as part of the project. I would like to acknowledge my parent’s encouragement and understanding, for this I am grateful and humbled. Ultimately their support and guidance has attributed to my overall happiness and ability to peruse the serious task of completing this thesis. Both my brother Wade and my sister Sheridan have been instrumental in keeping me motivated, sane and keeping me laughing, thank you. This research could not have been done without the help of volunteers. I am sincerely grateful for your help on many cold and murky dives and damp winter days by the water, Deborah Harrison, Liam Gregory, Chris Mabin, Daniel Pountney, Digory Hulse, Luke Neuman, Mark Blumhardt and Alex Inwood. My Fiancé Deborah Harrison’s support cannot be summed up in a brief sentence, or even another dissertation. My love and respect for her has grown with each passing day, Deborah’s i love for science and conservation has motivated me to push to achieve more than I thought possible. The years of this candidature have been a struggle, but it was a struggle we shared. ii ABSTRACT The theoretical understanding of invasion success is linked to a variety of drivers including enemy release, facilitation, and competitive ability. Within the marine environment, any bare solid substrate is quickly colonised making “free” space for settlement a limited resource. Consequently, the living surfaces of many species are subjected to the constant threat from overgrowth and/or epibiosis. Epibiosis presents a mechanism that eliminates the need to find bare space while increasing overgrowth success by settling on competitors. The ability of non-indigenous species (NIS) to see and use more types of space as “free” space may confer a competitive advantage to these species and requires greater investigation. As such the basis of this thesis is to explore epibiosis in NIS and native marine community assemblages. Theoretically, native species have co-evolved defence mechanisms against epibiosis, whereas they are naïve against epibiosis by NIS (and vice versa). Epibiosis is common, however a systematic review revealed a lack of information comparing native and NIS interactions, especially where the outcome of epibiosis was mortality. The pattern of epibiosis was examined within naturally assembled communities to understand native:NIS epibiotic interactions. Recruitment phenology was contrasted with settlement preferences and epibiotic pressures of both native and introduced species in communities of varying ages in northern Tasmania. Native species were found to have more interactions than expected with natives than with NIS. In contrast, NIS demonstrated no significant preferences between NIS, native and bare substrates: Thus, they see all space as available, compared to native species that show a preference for type of space to settle upon. Building on this, ex situ manipulative experiments were used to examine pairwise interactions controlling for propagule pressure, propagule arrival time and environmental iii factors hypothesised in the literature to influence recruitment and subsequent settlement success. The experimental outcomes demonstrate that native species experience greater epibiotic settlement by both native and NIS, whereas NIS were relatively free of epibiotic load. The multiple lines of evidence used in this dissertation have illustrated fundamental differences between marine native species and marine NIS, reinforcing the view that NIS are opportunistic settlers using a greater suite of substrates as available space than native species. Moreover, given that epibiosis generally comes at a cost to basibionts, a reduced epibiotic load on NIS compared to native competitors, infers a competitive advantage to NIS. iv Table of Contents ACKNOWLEDGEMENTS ........................................................................................................ i ABSTRACT ............................................................................................................................. iii LIST OF TABLES ................................................................................................................... vii LIST OF FIGURES ................................................................................................................... x LIST OF EQUATIONS .......................................................................................................... xiv GLOSSARY ............................................................................................................................ xv CHAPTER 1. INTRODUCTION ........................................................................................ 1 1.1 Background and significance ........................................................................................... 1 1.1.1 Invasion success ........................................................................................................ 3 1.1.2 Enemy release hypothesis ......................................................................................... 5 1.1.3 Competition............................................................................................................... 6 1.1.4 Epibiosis .................................................................................................................... 8 1.2 Conclusion and aims ...................................................................................................... 11 CHAPTER 2. A SYSTEMATIC REVIEW ....................................................................... 14 2.1 Introduction .................................................................................................................... 14 2.2 Methods.......................................................................................................................... 19 2.2.1 Data collection and criteria for inclusion ................................................................ 19 2.2.2 Data analysis ........................................................................................................... 20 2.3 Results ............................................................................................................................ 21 2.3.1 Benthic basibionts ................................................................................................... 22 2.3.2 Sessile and sedentary invertebrate basibionts ......................................................... 24 2.3.3 Bryozoan basibionts ................................................................................................ 25 2.3.4 NIS epibiont:NIS basibiont associations ................................................................ 26 2.4 Discussion ...................................................................................................................... 27 CHAPTER 3. RECRUITMENT PHENOLOGY .............................................................. 33 3.1 Introduction .................................................................................................................... 33 3.2 Methods.......................................................................................................................... 37 3.2.1 Location .................................................................................................................. 37 3.2.2 Artificial settlement collectors and deployment ..................................................... 38 3.2.3 Monthly recruitment ............................................................................................... 39 3.2.4 Recruitment and space occupancy .......................................................................... 41