EFFECTS OF ACIDIFIED SEAWATER ON ASEXUAL REPRODUCTION AND STATOLITH SIZE IN THE SCYPHOZOAN CHRYSAORA COLORATA A Thesis Presented to the Faculty of Moss Landing Marine Laboratories And California State University Monterey Bay In Partial Fulfillment of the Requirements for the Degree Master of Science in Marine Science by Thomas S. Knowles December 2012 iii Copyright © 2012 by Thomas S. Knowles All Rights Reserved iv DEDICATION I dedicate this work to my family and friends, whom I am very fortunate to have in my life. v It is advisable to look from the tide pool to the stars and then back to the tide pool again. – John Steinbeck, The Log from the Sea of Cortez vi ABSTRACT Effects of Acidified Seawater on Asexual Reproduction and Statolith Size in the Scyphozoan Chrysaora colorata by Thomas S. Knowles Master of Science in Marine Science California State University Monterey Bay, 2012 Absorption of anthropogenic atmospheric CO2 into the ocean surface is causing ocean acidification and chemistry changes that reduce calcification in organisms that form calcium carbonate skeletons and shells. Increased acidity also affects aspects of life history other than calcification, such as sexual reproduction and recruitment. Studies of scyphozoan jellyfish abundance have not reached a consensus on the effects of ocean acidification on jellyfish populations, and few laboratory studies have looked at the effects of acidified seawater on jellyfish biology. This study examined the effect of acidity on the benthic and early pelagic stages of the scyphozoan Chrysaora colorata and the formation of a calcium sulfate sensory structure, the statolith. Researchers who model future ocean surface pH levels predict a drop of 0.3-0.5 units from pre-industrial levels by 2100 if fossil fuel consumption continues at its current rate. To understand how these conditions will affect C. colorata, treatments of acidified seawater (pH = 7.85, 7.75, 7.65, and 7.55) and a control (pH = 7.97) were used to test the effects of ocean acidification on asexual reproduction (number of podocysts formed, number of new polyps formed, number of days to begin strobilation, duration of strobilation, number of healthy ephyrae released, and percentage of ephyrae that were healthy) and statolith size. There was no effect of acidity on asexual reproduction in C. colorata, but there was a significant negative effect of acidity on statolith size—this supports previous research on the scyphozoan Aurelia labiata. This study suggests that C. colorata will be able to survive and asexually reproduce from the polyp stage through the ephyra stage in near-future ocean conditions. Previous studies have shown that a lack of statoliths results in swimming abnormalities, but the effect of smaller statoliths is unknown. To fully understand how C. colorata will be affected by ocean acidification, further research needs to be conducted on other stages of the lifecycle. C. colorata and other scyphozoans play important roles in their ecosystems, and if their abundance is negatively affected then their predators, prey, and competitors will be affected as well. However, it is possible that the effects of ocean acidification on C. colorata and other scyphozoans will be subtle and that they could benefit from declines in the abundance of predators and competitors that are more sensitive to the chemistry changes of ocean acidification. vii TABLE OF CONTENTS PAGE ABSTRACT.........................................................................................................................vi LIST OF FIGURES........................................................................................................... viii ACKNOWLEDGEMENTS..................................................................................................ix INTRODUCTION.................................................................................................................1 Chrysaora colorata ..............................................................................................2 Statoliths..............................................................................................................4 METHODS ...........................................................................................................................7 Polyp Culture.......................................................................................................7 Experimental Manipulation of pH ........................................................................7 Statolith Measurement..........................................................................................9 Statistical Analysis...............................................................................................9 Treatment Validation ...........................................................................................9 RESULTS...........................................................................................................................11 Effects of Acidity on Asexual Reproduction.......................................................11 Swimming Observations ....................................................................................11 Effects of Acidity on Statolith Size.....................................................................11 DISCUSSION .....................................................................................................................14 Asexual Reproduction........................................................................................14 Statolith Size......................................................................................................14 Implications for Scyphozoans.............................................................................16 Further Research ................................................................................................17 LITERATURE CITED........................................................................................................18 viii LIST OF FIGURES PAGE Figure 1. An adult Chrysaora colorata in the pelagic environment (Photo: D. Wrobel). ....................................................................................................................2 Figure 2. (A) Podocysts of Chrysaora colorata photographed using a scanning electron microscope. (B) C. colorata polyp with an emerging stolon and podocysts that were formed by that polyp. .................................................................3 Figure 3. Statoliths of Chrysaora colorata in the statocyst.....................................................5 Figure 4. (A) One replicate—a 12 L “critter keeper” tank that was divided into 5 sections with 500 µm mesh. (B) Five dishes per replicate, one in each section, each starting with 1 polyp. (C) Styrofoam boxes serving as temperature baths, with filtered Monterey Bay seawater continuously flowing into the boxes, around the critter keepers, and then exiting the boxes. ........................................................................................................................8 Figure 5. (A) Mean pH (± 99% confidence intervals) in each replicate throughout the experiment. (B) Mean temperature (± 99% confidence intervals) in each replicate throughout the experiment. ................................................................10 Figure 6. Mean values ±SE of (A) the number of podocysts formed and (B) the number of new polyps formed. Each dot represents a replicate of 5 polyps......................................................................................................................12 Figure 6 cont. Mean values ±SE of (C) the number of days to begin strobilation, (D) the duration of strobilation, (E) the number of healthy ephyrae that were released, (F) the percentage of total ephyrae that were healthy, and (G) statolith size. Each dot represents a replicate of 5 polyps...................................13 Figure 7. The surface pH at Wharf 2 in Monterey, CA, from June to November 2012 (Moss Landing Marine Laboratories Public Data Portal). ................................16 ix ACKNOWLEDGEMENTS Funding for this project was obtained from the Monterey Bay Aquarium and from the The James Nybakken Scholarship and Friends of Moss Landing Marine Laboratories. I would like to thank my thesis committee: Jonathan Geller and Kenneth Coale of Moss Landing Marine Laboratories and Jim Barry of the Monterey Bay Aquarium Research Institute. This project benefited greatly from their world-class expertise, excellent guidance, and moral support. They spent many hours of their time making sure the science was sound and helping me to hone the thesis defense and final manuscript. Thank you especially to Jonathan Geller for being a great and supportive graduate school advisor during my time here at MLML, and thank you for being patient with my unorthodox schedule throughout the years. Ivano Aiello provided critical help with the measurement of the statoliths. He spent many hours helping me figure out how best to isolate and measure the tiny crystals, and he allowed me use of microscopes, cameras, and lab space in the MLML Geological Oceanography Lab. He also facilitated the use of the scanning electron microscope at MLML for photographing the podocysts. Mike Graham and Jim Harvey provided help with the statistical analysis. Both provided elegant solutions to difficult problems that I encountered during analysis of the data. Thank you to the MLML Invertebrate Zoology and Molecular Ecology Lab and the Monterey Bay