Aaron Dufault FINAL REVISIONS
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CALIFORNIA STATE UNIVERSITY, NORTHRIDGE THE EFFECTS OF OCEAN ACIDIFICATION ON THE PHYSIOLOGY OF CORAL RECRUITS A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Biology By Aaron Matthew Dufault December 2012 The thesis of Aaron Matthew Dufault is approved: Dr. Peter Edmunds, Chair Date Dr. Robert Carpenter Date Dr. Steve Dudgeon Date California State University, Northridge ii Acknowledgments I’d like to thank my advisor Dr. Pete Edmunds for his dedicated guidance throughout my MS research. I appreciate Dr. Edmunds’ commitment to fostering independent and critically minded students, which has helped me grow as a scientist while under his mentoring. I would also like to thank my committee members, Dr. Robert Carpenter and Dr. Steve Dudgeon for their constructive criticism, statistical advice and for bringing their own expertise to my project ideas. I am grateful to Dr. Vivian Cumbo for her advice, patience, and all around uplifting attitude while in the field. Your encouragement has helped me focus on the novelty of my findings, which I greatly appreciate. I would like to thank the other polyp lab members including Lianne, Jacobson, Sylvia Zamudio, Chris Wall and Darren Brown for their constructive input, field/lab assistance and their vital role in fostering my progress as a scientist during my time at CSUN. I would also like to thank fellow CSUN marine biology graduate students Anya Brown, Jenny Gowan, Jesse Tootell and Brenton Spies for their constructive input. I’d like to also acknowledge the crucial role of the lab of Dr. Tony Fan at the National Museum of Marine Biology and Aquarium (NMMBA) in Taiwan. Your assistance in the lab and the field were incredibly helpful in ensuring our experiments ran smoothly. Specifically I’d like to thank Yao-Hung Chen, Okay Chan, Neo Zong-yu Wu, John Chen Wei-ta, and Tony Yang. I am also very grateful for the assistance Hollie Putnam, Anderson Mayfield and Steve Doo provided while in the field. I would like to thank my fiancé and future wife Molly Kleinman for her support throughout this time. I appreciate your support and encouragement through my extended field trips and putting up with me working long hours even while home. This work would not have been performed if not for the financial support from the National Science Foundation (OCE 08-44785). Partial funding was also provided by CSUN Graduate Research and Internation programs, Associated Students, and University Corporation. iii TABLE OF CONTENTS Signature Page ii Acknowledgements iii Abstract v Chapter 1 General Introduction 1 Chapter 2 The effects of diurnally oscillating pCO2 on the calcification and survival of coral recruits Introduction 9 Methods 11 Results 18 Discussion 20 Tables 26 Figures 27 Chapter 3 The importance of light in mediating the effects of ocean acidification on coral recruits Introduction 31 Methods 35 Results 42 Discussion 44 Tables 51 Figures 53 Chapter 4 The response of carbonic anhydrase activity to ocean acidification: implications for coral calcification Introduction 57 Methods 59 Results 65 Discussion 66 Tables 69 Figures 71 Chapter 5 Conclusion 72 References 76 iv Abstract The Effects of Ocean Acidification on the Physiology of Coral Recruits By Aaron M. Dufault Master of Science in Biology Ocean acidification (OA), caused by the dissolution of anthropogenic CO2 into the surface waters of the ocean, threatens the fate of calcifying marine organisms. The effects of OA on adult coral calcification have been well-studied over the past decade and generally results in decreased calcification rates with increasing pCO2, although the effects of OA on early life history stages are less well-studied. This thesis addresses the effects of OA on coral recruit physiology with an emphasis on filling key gaps in the ecological relevance of previous manipulative OA coral studies. Chapter I: In March and June 2010, two experiments were conducted exposing newly settled Seriatopora caliendrum recruits to low (440, 456 µatm), high (663, 837 µatm; March,June respectively) and diurnally oscillating pCO2 which mimicked the conditions at Hobihu reef, Taiwan where adult corals were collected. Calcification and survival of coral recruits was elevated in diurnally oscillating pCO2 relative to static ambient and high pCO2, hypothesized to be the result of increased DIC stored in coral tissues at night. Chapter II: In March 2011, newly settled Pocillopora damicornis recruits were exposed to low (493 µatm) and high pCO2 (878µatm) in varying light intensities (226, 122, 70, 41, 31 µmol photons m-2 s-1) to test the effects of light and OA on coral recruit physiology. Coral recruit calcification and survival in both pCO2 treatments was light-dependent, with v large differences in calcification at intermediate light intensities (41, 70 µmol photons m-2 s-1) though calcification at high and low light intensities did not differ (226, 31 µmol photons m-2 s-1). Survivorship was not correlated with size and was highest in both -2 -1 ambient and high pCO2 at 122 µmol photons m s . Chapter III: Finally, the activity of carbonic anhydrase in S. caliendrum juveniles (< 3 cm ) exposed to ambient, high and diurnally oscillating pCO2 was measured to elucidate the mechanistic basis for increased calcification in diurnally oscillating pCO2. CA activity was decreased in both high and diurnally oscillating pCO2 during the day, which is consistent with the DIC buildup hypothesis proposed in Chapter I. Together these findings provide novel insight into the physiology of corals exposed to OA under ecologically relevant seawater chemistry and light conditions. Coral recruits are biologically quite different than their adult counterparts therefore further work is needed to determine the extent to which these results apply to adult corals. vi Chapter 1 Introduction Ocean acidification and Corals Current atmospheric CO2 concentrations are unprecedented over the last 800,000 y (Tripati et al. 2009), and present levels of ~ 391 ppm are predicted to rise to > 800 ppm by 2100 due to the continued burning of hydrocarbon-based fuels (A2 scenario, IPCC 2007). Rising atmospheric CO2 has two primary implications for marine organisms: 1) increased atmospheric CO2 causes an enhanced greenhouse effect leading to warmer ocean temperatures, and 2) atmospheric CO2 dissolves into the surface waters of the ocean, leading to a process called ocean acidification. The enhanced greenhouse effect is predicted to raise global mean temperatures by ~ 4°C by the year 2100 (Sokolov et al. 2009) which stands to effect marine organisms around the earth (Doney et al. 2009). Ocean acidification is the coined term describing the following series of reactions that take place as anthropogenic CO2 dissolves into the surface waters of the ocean: Equation 1: CO2 g ↔CO!(aq), CO2 aq +H2O l ↔H2CO3 aq , + - H2CO3 aq ↔H aq +HCO3(aq), + 2- HCO3 aq ↔H aq +CO3 (aq) The results of anthropogenic CO2 dissolving into ocean waters are the net 2- - decrease in pH and CO3 and increased pCO2, HCO3 , and total dissolved inorganic carbon (DIC). By the year 2100, ocean pH is predicted to decrease by as much as 0.5 units from current levels (Caldeira and Wickett 2003). For many calcifying marine organisms, OA decreases the rate of biogenic CaCO3 deposition used to create their 1 skeletons (Doney et al. 2009). The cause of this decline in calcification often is attributed - 2+ to a decrease in the availability of CO3 that can combine with Ca to form CaCO3. - However the source of inorganic carbon used in the calcification process, whether HCO3 2- - or CO3 is a debated topic (Jury et al. 2010). Biological evidence points towards HCO3 being the primary external source of carbon for calcification due to the identification of - HCO3 transporters in a wide range of invertebrate and vertebrate taxa including corals 2- (Furla et al. 2000). No CO3 transporter has been identified in corals, although a strong 2- positive correlation between [CO3 ] and coral calcification rates remains for most corals (Schneider and Erez 2006, Erez et al. 2011, Allemand et al. 2011, Pandolfi et al. 2011). Recent evidence reveals calcification of a few corals remaining unaffected or stimulated 2- by increased pCO2 under certain conditions (i.e., decreased CO3 , Anthony et al. 2008, Jury et al. 2010, De Putron et al. 2011). Despite the few examples of negligible or increased calcification by corals in OA conditions, these studies highlight the complexities of the biogenic calcification process and suggest responses by corals to OA may be more diverse than previously thought (Jury et al. 2010). Decreased calcification instead may be the result of multiple interactions between increased pCO2, decreased pH, and the change in the concentrations of DIC species resulting from OA, although it has not been tested thoroughly (except Schneider and Erez 2006, Jury et al. 2010). OA and early coral life history stages In a recent review on the effects of OA on corals, ~25 scleractinian coral species throughout the past decade have been empirically tested in OA conditions (Erez et al. 2011), a mere 3% of the total 794 species scleractinian order (Veron 2000). The majority 2 of these studies have tested the response of adult corals to OA, and only recently have early life history stages (larvae/recruits/juveniles) been explored (Albright et al. 2008, Cohen et al. 2009, Albright 2011). There is reason to believe early life history stages are biologically quite different from their adult counterparts (Hamdoun and Epel 2007), as this life history stage marks a crucial transition from a solitary pelagic larva to a colonial benthic sedentary existence. For coral recruits, their size often determines their ability to withstand environmental perturbations, and it influences their competitive ability with other corals, invertebrates and macroalgae, which all are competing for similar benthic substrata (Babcock 1991, Dunston et al.