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Thermal Tolerance and the Potential Effects Of THERMAL TOLERANCE AND THE POTENTIAL EFFECTS OF CLIMATE CHANGE ON COASTAL INTERTIDAL AND ESTUARINE ORGANISMS IN THE KARIEGA ESTUARY AND ADJACENT INTERTIDAL COASTLINE, EASTERN CAPE, SOUTH AFRICA A thesis submitted in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY of RHODES UNIVERSITY By KERRY-ANN VAN DER WALT December 2019 ABSTRACT Temperature changes due to the effects of climate change are evident on all continents and oceans. As a result, there is a growing concern over how marine ectotherms will respond to extreme or fluctuating environmental temperatures. Temperature changes have strong direct and indirect effects on individual, population, and ecosystem functioning traits. A multi-scale approach determining the thermal tolerance and performance of several marine ectotherms belonging to different coastal habitats is rarely considered in thermal physiology studies but is effective for an integrated ecosystem assessment. As such, for this thesis, I aimed to quantify and compare the thermal tolerance and performance of a range of coastal marine ectotherms (fish and macro-invertebrates) with different biogeographical distributions from estuarine, subtidal and rocky intertidal habitats to available and projected in situ temperature data. This was also undertaken to gauge the local vulnerability of each species across summer and winter in a warm-temperate region of South Africa. This was done using a multi-method physiological approach, which included the dynamic method (CTmax and CTmin), static respirometry and maximum heart rate f Hmax). Results of the dynamic method on several fish and macro-invertebrate species indicated that there are differences in thermal tolerance according to taxonomy, biogeography and habitat for both summer and winter. Macro-invertebrate species generally had higher CTmax endpoints, lower CTmin endpoints, higher upper and lower breadths in tolerance, higher upper and lower thermal safety margins and higher thermal scopes than the fish species. This could be a result of the macro-invertebrate species studied being less mobile compared with fish species (which are able to move to more favourable conditions) as well as having broader geographical distributions. In addition, macro-invertebrates from the intertidal rock pool habitat (Palaemon peringueyi; Pernaperna) were more tolerant of high and low temperatures compared with the macro-invertebrates from the estuarine habitat (Clibanarius virescens; Parasesarma catenatum; Upogebia africana). Overall, macro-invertebrates, with the exception of Parechinus angulosus, investigated in this study indicated that current temperatures and projected climate change scenarios across seasons would not have a significant impact on them and that they are highly adaptable to changing temperature regimes. This sign of high tolerance was further supported by the heart rates of P. perna and P. catenatum under an acute increase ii in temperature (1.0 °C.h-1) which showed individuals of each species physiologically depressing their metabolism until a final Arrhenius breakpoint temperature was reached (TAB). Among the fish species investigated in this study, tropical species (Chaetodon marleyi; Kuhlia mugil) had the highest CTmax and CTmin endpoints when compared with the temperate (Diplodus capensis; Sarpa salpa), warm-water endemic (Chelon dumerili; Rhabdosargus holubi) and cool-water endemic (Chelon richardsonii) fishes. This suggests that due to their lower breadths in tolerance and thermal safety margins being small, tropical species may be less tolerant of cold temperatures and thermal variability, especially in the form of summer upwelling events which are expected to increase in intensity and frequency in this region as a result of anthropogenic climate change effects. On the other hand, however, if a temperature increase of 2.0 - 4.0 °C takes place at the end of the century as predicted by the Intergovernmental Panel on Climate Change (IPCC), it is likely that tropical species such as C. marleyi will become more common. Temperate species such as D. capensis and S. salpa were able to tolerate a wide range of temperatures (wide thermal scope) compared with the other fish species. These findings may suggest that D. capensis and S. salpa are thermally resilient and may be the least vulnerable to climate change effects and temperature variability. When evaluating the different life stages of D. capensis, however, using the dynamic method (juveniles and adults), static respirometry (juveniles) and maximum heart rate (adults), results suggested that juveniles of this temperate species will be more resilient to increases in ocean temperatures compared with the adults because they have a higher thermal tolerance (CTmax/TCRIT) and a greater metabolic scope (TOPT) at higher temperatures. For both juveniles and adults, temperatures beyond 28.0 °C (upper Tp e j; Ta r r ) will have a significant impact on their physiology. Using a multi-scale and multi-method approach thus helped to identify which species or community may be vulnerable to the effects of climate change within shallow coastal environments in this warm-temperate climate change hotspot. Adopting this type of approach will assist policy makers in developing comprehensive climate change management frameworks for coastal ecosystems globally and around South Africa. iii DECLARATION I, Kerry-Ann van der Walt, hereby declare that the work described in this thesis was carried out in the Department of Ichthyology and Fisheries Science, Rhodes University and the South African Institute for Aquatic Biodiversity, under the supervision of Dr NC James, Professor WM Potts and Dr F Porri. The components of this thesis comprise original work by the author and have not been submitted to any other university. Kerry-Ann van der Walt 12/12/2019 Date iv DEDICATION This thesis and work is dedicated to my mother, Penny, and my sister, Amy-Leigh. To the two strongest women I know, thank you for all your unconditional love and support! v ACKNOWLEDGEMENTS I would like, foremost, to thank my supervisors, Dr Nikki James, Dr Warren Potts and Dr Francesca Porri for their support, guidance and patience during this thesis. Nikki, thank you for allowing me the opportunity to do this project and all the funding that you provided. Warren, thank you for all your advice. Francesca, thank you for your constant motivation and reassurance throughout this journey, those quick pop ins’ to your office to ask a small question which then turned into a long constructive brainstorming conversation (with some added humour or tissues) meant so much to me and I am truly appreciative. I acknowledge, and am extremely thankful for, financial support for this research from the National Research Foundation who awarded me with an NRF Innovation Doctoral Scholarship, a NRF Extension Scholarship and a research development y-rated grant through my supervisor, Dr Nikki James. A special acknowledgement goes to the South African Institute for Aquatic Biodiversity (SAIAB) who provided funding post my extension funding for me to complete this thesis. I would also like to thank SAIAB for the incredible working environment that was made available to me, the use of its vehicles and boats to conduct my research, and the use of the workshop where all my newly founded electrical, engineering and technical skills came into play to build my experimental system. Thank you Francois Lamont for helping and showing me how to put these newly founded skills to work and thank you Matt Parkinson for always having Aestuaria ready to go for field work. Ferdinand Jacobs, thank you for always making sure I had a vehicle, even at the last moment. Overall, SAIAB thank you for being the foundation in this journey, arriving to a friendly environment where everyone is so helpful and caring is so motivating and definitely lifted my spirits, especially during the hard parts of this journey. Enkosi kakhulu SAIAB family! Another special thanks goes to the staff and students at the Department of Ichthyology and Fisheries Science (DIFs) and the Zoology Department, Rhodes University. Dave Drennan, thank you for helping with my experimental system in the Ecophysiology Lab. Whenever there were technical difficulties and silly problems that always seemed to crop up, you were there and were willing to come help, even after hours while I was running my experiments. Matt van Zyl, thank you for going to collect seawater for me and for helping me collect blacktail during vi the RASSPL competitions, getting stuck on the beach was definitely an adventure (we did have permits to drive on the beach, thank you Paul Cowley). Thanks also goes to all the students from both SAIAB and DIFs that helped with field work and a special thanks goes to Dr Amber Childs, Dr Alex Winkler, Dr Murray Duncan, Mike Skeeles and Brett Pringle for helping with the blacktail heart rate experiments and surgery. Dr Cristian Monaco and Dr Morgana Tagliarolo, thank you for the assistance provided during the heart rate analysis, and Prof. Christopher McQuaid, thank you for allowing me the use of your lab to conduct the heart rate experiments. To Seshnee Reddy, my dearest friend, I can’t thank you enough for being there for every field trip, every experiment and every emotional breakdown. Words enough cannot express my gratitude for everything you have done for me during this journey. Thank you for staying with me to all hours during the experiments, having you there always made it easier, even when we hit crazy hour because we were so tired, and especially when we nearly got trapped in shed 7, your strength physically and emotionally got me through tough times, thank you. To my partner, my skipper, my diver, my expert butterflyfish collector, my ultimate number one supporter, Dr Terence Bellingan, thank you for all your love, support, understanding and patience. You took the time out of your PhD to always help me with mine, and never gave up on collecting every single fish I needed when I was ready to. You truly were my pillar of strength through all of this, and your constant motivation and words of encouragement definitely helped me get through this.
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