California State University, Northridge Effects of Age
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CALIFORNIA STATE UNIVERSITY, NORTHRIDGE EFFECTS OF AGE AND SIZE ON THE GROWTH AND PHYSIOLOGY OF SCLERACTINIAN CORALS A thesis submitted in partial fulfillment of the requirements For the degree of Master of Science in Biology By Robin Elahi December 2005 The thesis of Robin Elahi is approved: ___________________________________ ________________ Robert C. Carpenter, Ph.D. Date ___________________________________ ________________ Steven R. Dudgeon, Ph.D. Date ___________________________________ ________________ Brian S. T. Helmuth, Ph.D. Date ___________________________________ ________________ Peter J. Edmunds, Ph.D., Chair Date California State University, Northridge ii Acknowledgements The completion of this thesis would have been impossible without the support of many people, and to all I am grateful, including numerous individuals not specifically acknowledged. First, I would like to thank my primary advisor, Dr. Pete Edmunds, for the opportunity to join the Polyp Lab. I am a better scientist, and person, as a direct result of the countless enjoyable hours we shared in the classroom, field and laboratory. The development and execution of this project benefited greatly from the many discussions I had with my committee members, Drs. Bob Carpenter, Steve Dudgeon, and Brian Helmuth. Thoughtful insight was provided by Drs. Ruth Gates, Dave Gray, Fritz Hertel, and Paul Wilson on several occasions. Many people assisted with fieldwork, especially Christina Buck and Mike Murray, as well as Laurie Allen-Requa, Danny Green, Joshua Idjadi, Sarah Lee, Mairead Maheigan, and students of the Threes Seas XX and XXI program. The staff at the Discovery Bay Marine Laboratory and the Richard Gump Station was very hospitable and helpful. The Northeastern University Three Seas Program spearheaded my graduate career, supported my research efforts extensively in Jamaica and Moorea, and I thank Dr. Sal Genovese for his help over the past three years. This research was additionally funded by P.A.D.I Project Aware, CSUN University Corporation (#620200), CSUN Associated Students, CSUN Graduate Studies, Research & International Programs, Sea Grant Program of the University of Puerto Rico (#R-101-2-02), NSF-LTREB (DEB 03443570), and NSF-LTER (NSF-OCE 041412). Vickie Everhart, Linda Gharakhanian, and Cherie Hawthorne in the CSUN Biology Department made my life easier by resolving many bureaucratic issues. My CSUN peers reminded me there was more to life than research; in particular I thank Kylla Benes, Peter Holmquist, Becca Kordas, Pavel Lieb, Mairead Maheigan, Kathy Morrow, and Mike Murray for their friendship. Finally, I am grateful to my parents for unconditionally supporting my endeavors. I thank my mother for instilling in me a sense of adventure, and my father for pushing me academically. Without their strong influence my life would be far less interesting. iii TABLE OF CONTENTS Signature page ii Acknowledgements iii Abstract v Chapter 1 - General introduction 1 Chapter 2 - The effects of age and size on the physiology of the branching coral, Madracis mirabilis I. Introduction 7 II. Methods 10 III. Results 15 IV. Discussion 17 V. Tables and figures 23 Chapter 3 - The consequences of fission in the massive coral Siderastrea siderea: growth rates of small colonies and clonal input to population structure I. Introduction 28 II. Methods 31 III. Results 35 IV. Discussion 37 V. Tables and figures 40 Chapter 4 - Energetic constraints on indeterminate growth in the solitary coral, Fungia concinna I. Introduction 44 II. Methods 49 III. Results 60 IV. Discussion 65 V. Tables and figures 70 Chapter 5 - Concluding remarks 79 Literature Cited 83 iv ABSTRACT EFFECTS OF AGE AND SIZE ON THE GROWTH AND PHYSIOLOGY OF SCLERACTINIAN CORALS By Robin Elahi Master of Science in Biology The growth of modular organisms is achieved by the asexual iteration of conserved units, and the biological implications of this type of growth are vast. One direct consequence of modularity is the potential for exponential growth through asexual reproduction and dispersal, thereby removing the genotype from the physiological constraints of senescence and permitting it to become virtually immortal. However, senescence at the level of individual modules may still exist. Scleractinian corals are an excellent model system to test for effects of age and size because colonies often experience fission, fusion, and fragmentation, thereby decoupling the relationship between age and size. Understanding how fission and fragmentation affect coral growth is timely because the likelihood of partial mortality and fission will increase due to global degradation of coral reefs, resulting in large numbers of small, yet old, colonies. In order to test the effects of age and size on growth in corals, two approaches were taken. First, age and size were manipulated experimentally by breaking branches of the coral, Madracis mirabilis, into young and old fragments, and growth subsequently was quantified as calcification rate. Growth scaled isometrically in both age groups, and although scaling exponents were statistically indistinguishable among ages, young fragments calcified faster than old fragments. In other words, the effect of age was absolute and independent of size. The second approach involved a mensurative analysis of the massive coral, Siderastrea siderea. This species often undergoes fission to produce small daughter colonies that are old. The growth of similarly sized sexual recruits (young) and daughter colonies (old) was monitored for a year, and these two colony types exhibited significant differences in lateral extension. Furthermore, age affected the scaling of calcification so that young corals grew disproportionately faster than old corals over the smallest size range. Together, the experiments with M. mirabilis and S. siderea demonstrate that age significantly affects coral growth, and suggest that the rapid growth of juvenile corals can be attributed to their young age, rather than their small size. Although most scleractinian corals are modular, certain species are not, and thus the relationship between age and size typically is predictable. In contrast to colonial corals that grow indeterminately and are typically only limited by space, solitary species are likely to exhibit an upper maximum size that may result from energetic constraints. An energetic model originally developed for anemones was modified in order to test the hypothesis that energetic constraints limit the maximum size of the solitary coral Fungia concinna. The model assumed that photosynthesis was the primary source of energetic intake and metabolic cost was quantified as aerobic respiration. The scaling exponent on v mass was higher for energetic intake than metabolic cost, allowing large individuals to maintain an energetic surplus over the size range studied, even when the energy required for daily host tissue and symbiont growth was incorporated into the model. Therefore, it appears that growth in F. concinna is not limited energetically. Instead, mechanical constraints on locomotion may set the maximum size of this solitary coral. The results of these three studies demonstrate clearly that age and size separately affect the physiology of solitary and modular corals, but also highlight the potential for interactive effects of these two demographic parameters that likely are under strong selective pressure. vi CHAPTER 1 General introduction Organisms that grow by the repeated iteration of multicellular parts, or modules, are defined as modular (Harper 1977). In contrast, solitary organisms grow by increasing the size of a single unit, which typically begins as a zygote that first undergoes development. A variety of organisms display modularity (i.e., clonality), including algae, higher plants, fungi, cnidarians, bryozoans and ascidians. The biological implications of modularity are vast, and have been reviewed by Jackson et al. (1985) and by many authors in an issue of the Philosophical Transactions of the Royal Society of London B devoted solely to the growth and form of modular organisms (Harper et al. 1986). Some of the recent work on modular invertebrates has focused on the morphological integration of complex colonial forms (Gateño & Rinkevich 2003, Nakaya et al. 2003, Sánchez 2003, Kaandorp et al. 2005), allorecognition responses of self and non-self clones (Chadwick-Furman & Weissman 2003, Cadavid 2004), and the constraints on modular growth (Kim & Lasker 1998, Tanner 1999, 2002). One direct consequence of modularity is the potential for genetic individuals (hereafter referred to as genets) to grow exponentially through asexual reproduction, whereas solitary organisms are typically subject to allometric constraints on size (Gould 1966, Schmidt-Nielsen 1984). As a result, clonal organisms can become locally abundant in both terrestrial and marine habitats. Modular design also allows the genet to fragment into physically unattached, viable individuals of the same genotype (hereafter referred to as ramets). This can provide the genet with asexual dispersal opportunities, 1 and can spread the risk of mortality over a large area, as observed for clonal plants (Harper 1985) and many benthic invertebrates (Jackson 1985). As a result, the clonal propagation of ramets can theoretically confer “immortality” upon a genet (Jackson & Coates 1986). In other words, genets may not experience an increase in mortality rates with advancing age (Caswell 1985), which is the original definition of senescence (Medawar 1952).