Investigating the effects and potential impacts of lionfish (Pterois spp.) in low salinity habitats. Submitted by Rebekah Trehern to the University of Exeter for the degree of Masters by Research in Biological Sciences in April 2019. Supervisors: Dr Lucy Hawkes and Dr Travis Van Leeuwen This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all material in this thesis which is not my own work has been identified and that no material has previously been submitted and approved for the award of a degree by this or any other University. 1 Abstract In this thesis, I use physiological and behavioural experiments in a laboratory environment to assess the impacts and potential effects of the invasive lionfish (Pterois spp. (Wilcox et al. 2018)) in a mangrove ecosystem. Chapter 1 of the thesis is a general introduction to the main theme of the thesis “lionfish in mangroves”. In this chapter, I present an introduction to invasive species, a general background about the introduction of lionfish in the Western Atlantic and wider Caribbean, the importance of mangrove ecosystems, and then end with the recent discovery of lionfish in mangrove ecosystems. Chapters 2 and 3 are the data chapters of the thesis. In Chapter 2, lionfish were reared in aquaria in the Bahamas under differing salinity treatments (37 ppt (typical reef ecosystem salinity), 20 ppt (typical mangrove ecosystem salinity) and 10 ppt (typical mangrove ecosystem salinity during low tide)) for 84 days. This experiment investigated the effect of acute hyposalinity on growth rate, metabolic rate (standard metabolic rate (SMR), maximal metabolic rate (MMR) and aerobic scope (AS)), maximum food consumption, feeding rates and specific dynamic action (SDAMax, SDAScope, SDATotal, SDADuration). Most lionfish survived in hyposaline conditions for 84 days until the conclusion of the experiment, however, various aspects of their physiology were effected. Lionfish feeding and aerobic capacity (MMR and AS) were reduced, whereas digestive duration (SDADuration) increased at the lowest salinity. Therefore, I suggest: 1) given the ability of lionfish to tolerate low salinity, updated range expansion models should incorporate salinity data to improve accuracy of predicted range expansion for lionfish, and 2) the invasion of lionfish in mangrove habitats with low salinity, although a serious concern, will unlikely lead to the same level of population increase, habitat destruction and decline in native fish populations as observed for some 2 Caribbean coral reef habitats. In Chapter 3, I explore the potential impact of lionfish on a native fish species, which typically occupies a similar trophic niche as lionfish in an invaded mangrove ecosystem, the Schoolmaster snapper (Lutjanus apodus). Using a habitat competition experiment in the laboratory at two salinity treatments (10 ppt (typical mangrove ecosystem salinity during low tide) and 37 ppt (typical reef ecosystem salinity)), I investigated the behavioural interactions between invasive lionfish and native Schoolmaster snapper in a simulated mangrove ecosystem. Schoolmaster snapper showed, on average, a 53% reduction in shelter use when in the presence of lionfish. Results suggest that lionfish have the ability to displace snapper from shelter and are therefore likely to increase the vulnerability of native mangrove fish species to predation by other mangrove meso-predators. Using a behavioural ethogram, I further identified key behaviours displayed by both fish species during a period in which lionfish and snapper both had access to shelter. However, salinity had no effect on the occurrence and outcome of these behaviours, despite my findings in Chapter 2. Chapter 4 is the general discussion of the thesis where I draw on previous research, as well as research from this study to place in context the novel threat of the lionfish invasion in mangroves. Overall, this thesis investigates the invasiveness of lionfish in a mangrove ecosystem by demonstrating their ability to tolerate and function in low salinity water for extended periods. 3 Table of Contents Table of Contents ........................................................................................... 4 List of Tables .................................................................................................. 6 List of Figures ................................................................................................ 7 Author’s Declaration .................................................................................... 10 Acknowledgements ..................................................................................... 11 Chapter 1: General Introduction ................................................................. 13 An introduction to invasive species .......................................................... 13 Lionfish and their invasion ......................................................................... 14 The importance of mangrove habitats ....................................................... 16 Lionfish in mangroves ................................................................................. 17 Thesis research ........................................................................................... 17 Chapter 2: Tolerances of a marine invader: bioenergetic responses of lionfish (Pterois spp.) to an environment of lowered salinity. ................. 22 Introduction .................................................................................................. 22 Methods ........................................................................................................ 27 Animal capture and transport ..................................................................... 27 Lionfish husbandry and feeding ................................................................. 28 Salinity treatments ...................................................................................... 30 Measuring metabolic rates ......................................................................... 30 Measuring maximal metabolic rate (MMR) ................................................ 32 Standard metabolic rate (SMR) and determination of aerobic scope (AS) 33 Specific dynamic action (SDA) ................................................................... 33 Calculations and statistical analyses .......................................................... 34 Ethics.......................................................................................................... 35 Results .......................................................................................................... 35 Growth, average prey consumption time and maximum food consumption ................................................................................................................... 35 Standard metabolic rate, maximal metabolic rate and aerobic scope ........ 36 Specific dynamic action .............................................................................. 36 Mortalities ................................................................................................... 36 Discussion .................................................................................................... 37 Figures and Tables ...................................................................................... 43 Chapter 3: The lion, the fish, and the mangrove: interactions between Schoolmaster snapper and invasive lionfish in a simulated mangrove ecosystem .................................................................................................... 48 Introduction .................................................................................................. 48 Methods ........................................................................................................ 53 4 Animal capture and transport ..................................................................... 53 Animal rearing, husbandry and feeding ..................................................... 53 Salinity treatments ...................................................................................... 54 Behavioural interactions ............................................................................. 54 Video analysis ............................................................................................ 55 Behavioural ethogram ................................................................................ 56 Calculations and statistical analyses .......................................................... 56 Ethics.......................................................................................................... 56 Results .......................................................................................................... 57 Discussion .................................................................................................... 58 Figures and Tables ...................................................................................... 64 Chapter 4: General Discussion .................................................................. 71 Bibliography ................................................................................................. 74 5 List of Tables Table 1.1 A comprehensive list of publications identifying lionfish in mangroves and other low salinity habitats including: location, methodology and main conclusions……………………………..…………………..………………………..19