CALIFORNIA STATE UNIVERSITY, NORTHRIDGE ANTHROPOGENIC STRESSORS AND THE IMPACTS ON SCLERACTINIAN AND NON-SCLERACTINIAN TAXA A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Biology By Ashley Elizabeth Potter December 2018 This thesis of Ashley E. Potter is approved by: Robert C. Carpenter, PhD. Date Hollie Putnam, PhD. Date Peter J. Edmunds, PhD., Chair Date California State University, Northridge ii ACKNOWLEDGEMENTS First and foremost, I would like to thank my super awesome advisor, Dr. Pete Edmunds who has always encouraged me to a better scientist and a better person, through his own actions. Pete’s mentorship has given me the tools I need to prepare for challenges and opportunities. He has also invested a tremendous amount of time and energy in order to allow me to have opportunities that further my career as a scientist. He is remarkably dedicated to all his students and their futures and even though he is a rock star, he always makes time for us. I feel very proud to have done a master’s with Pete and will use the skills I have learned for the rest of my life. Thank you so much Pete. I would like to thank my committee members, Dr. Robert Carpenter and Dr. Hollie Putnam putting up with me and providing me with their time and counsel. Their guidance was invaluable to my thesis work at CSUN and aided in making me a better scientist. Thank you to Hollie who helped support me as an undergraduate and really influenced my decision to join Pete’s lab. I am so eternally grateful to have such amazing, inspiring fellow graduate students and faculty in the Biology department at CSUN who went out of their way to help me with my thesis work. First, I am so grateful to ALL the members of the polyp lab (past and present) that I interacted with during my time at CSUN. Specifically, I would like thank Steve Doo for being my zen rock out in the field, Jesse Bergman who I just find really cool, and Hannah Nelson for going out of her way to help me with statistics. I also want to acknowledge my new lab mates (Megan Williams and Jack Girard) who have been a huge support system while writing my thesis. Furthermore, I am thankful to Nyssa Silbiger, Casey terHorst, and Georgios Tsounis for working with me on my statistics and bearing with all of my questions. All of you have been tremendously supportive and encouraging and I am so lucky to have been chosen for this lab. Finally, I would like to thank my family for their never-ending love and support through my masters. My sister (Shelby) whom I look up to and who inspires me to live my best life. My mom (Cookie) who always believed in me. My dad (Ray) who kept me grounded with my head on straight. My brother (Matt) who was always my super support system. And a very special and warm thank you to my partner in crime, Paco, who has endless understanding, support, and patience for me and my scientific pursuits. This work was made possible by financial support from the National Science Foundation to the Mo’orea Coral Reef, Long-Term Ecological Research site (OCE 16-37396). The work was also partially funded by the CSUN Research and Graduate Studies Office, and CSUN Associated Student. iii TABLE OF CONTENTS Signature Page……………………………………………………………………….ii Acknowledgements…………………………………………………………….…....iii Abstract……………………………………………………………………………....v Chapter 1: General Introduction…………………………………………………1 Chapter 2: Effects of natural disturbances non-scleractinian benthic invertebrates Introduction……………………………………………….….13 Methods…………………………………………………...….17 Results………………………………………………………..20 Discussion……………………………………………………22 Figures/Tables ………………………………………………..28 Chapter 3: Characterizing the Metabolic Gradient of Two Reef Corals: Understanding More than Just Highs and Lows Introduction………………………………………………… 35 Methods……………………………………………...……...38 Results ………………………………………………………47 Discussion…………………………………………………..49 Figures/Tables………………………………………………59 Chapter 4: Concluding Remarks………………………………………………..68 Literature Cited……………………………………………………….……………..72 iv ABSTRACT Anthropogenic stressors and the impacts on scleractinian and non-scleractinian taxa By Ashley E. Potter Master of Science in Biology Coral reefs are one of the most diverse ecosystems in the world and this diversity is largely due to the abundance and range of invertebrate taxa that live within the reef. Stony corals and sponges are two benthic taxa that provide numerous benefits to coral reef communities that can be affected by anthropogenic disturbances. This thesis is comprised of two studies that address the ecological or physiological implications of anthropogenic disturbances on shallow coral reef communities. The first study took an ecological approach by addressing two morphologically distinct sponge species (Ircinia campana and Niphates digitalis) and their associated fauna, in St. John, US Virgin Islands, following two category five hurricanes. N. digitalis was 52% more abundant (individual m-2) on the reefs of St John then I. campana. Hurricanes effects did not significantly decrease density of either sponge, but they did decrease sponge size for both species. N. digitalis housed more invertebrate fauna (Ophiothrix suensoni, and Pelia mutica) per unit length, then I. campana but this epifauna-host relationship did not appear to be obligate and changed over time. The second study took a physiological approach by measuring, for the first time, the metabolic scope of two corals, Pocillopora verrucosa and Acropora pulchra, that are important components of the resilient reefs of Mo’orea, French Polynesia. Using a v metabolic uncoupler to elicit the maximum metabolic rate (MMR), and starvation to elicit the basal metabolic rate (BMR), I described the gradient of metabolism and placed the metabolic rates associated with polyp expansion and digestion along this gradient. The metabolic scope ([MMR-BMR]/BMR) was ~136% for P. verrucosa and ~251% for A. pulchra, with metabolism increasing with expansion ~48-94%, and ~18-43% with digestion. I also explored size dependent metabolism and assessed if scaling differs based on organismic activity. The metabolic scaling exponents differed significantly among several treatments (b = 0.2 to 1) and differed from the exponents (b = 0.67 to 1) proposed by the metabolic level boundary (MLB) hypothesis. Variation in the scaling exponent was potentially caused by behavioral differences among the polyps. Together the results from Mo’orea, French Polynesia, and St. John US Virgin Islands, demonstrate the importance of studies that address the extent to which scleractinian and non-scleractinian taxa are being impacted by natural disturbances. They also highlight the need for ecological and physiological studies on coral reefs to determine how these stressors effect coral reef community structure and function. vi CHAPTER 1 General Introduction Anthropogenic Stressors on Coral Reefs Coral reefs are one of the most diverse ecosystems in the world, and are often compared to their terrestrial equivalent, the tropical rain forest (Connell 1997). This high diversity is due largely to the abundance and types of invertebrates that live within coral reefs (Glynn and Enochs 2011; Romero et al. 2015). Scleractinians, or hard corals, are critical invertebrates on coral reefs because they are essential ecosystem engineers (Jones et al. 1994). This means that they provide resources to other species, such as complex three-dimensional habitats that make up the reef structure (Jones et al. 1994). Their framework provides coastal protection, tourism, fisheries, raw materials for biomedical research, habitat, feeding, spawning, and nurseries (Moberg and Folke 1999). Because of their ecological importance, scleractinians have garnered much research attention over the last few decades. Coral reef ecosystems are constantly being challenged by a suite of natural and anthropogenic stressors that include, but are not limited to, ocean acidification (Hoegh-Guldberg et al. 2007), eutrophication (Fabricius 2005), disease (Birkeland 1997), rising sea surface temperature (Hoegh-Guldberg et al. 2007), and hurricanes (Harmelin-Vivien 1994), all of which can restructure coral reef communities. As some of these disturbances continue to increase in intensity due to climate change (Solomon et al. 2007; Knutson et al. 2010), it is critical to understand to what extent corals are being impacted by these events, both ecologically and physiologically, and to determine how this effects coral reef community structure and function. 1 Coral Reef Communities in Transition The increase in intensity of stressors in coastal tropical seas may cause major or minor shifts in coral reef community structure depending on the severity, duration, and return time of the perturbations (Woodley et al. 1981; Gardner et al. 2005). In recent decades, there have been ecologically significant losses in coral cover on the Great Barrier reef (De’ath et al 2012; Hughes et al. 2018), Florida Keys (Porter et al. 2001;), and large portions of the Caribbean (Gardner et al. 2003; Jackson et al. 2014). These effects range from 20 to > 90% decline in coral cover (Porter et al. 2001; Gardner et al. 2003; De’ath et al 2012; Edmunds 2013; Jackson et al. 2014; Hughes et al. 2018). Major drivers of the decline in coral cover throughout the Caribbean can be attributed to local disturbances including the regional-scale mortality of Diadema antillarum in 1983 (Levitan 1988; Edmunds and Carpenter 2001), tropical storms (Woodley et al. 1981; Rogers et al. 1991), and