Effects of Macroalgae on Coral-Microbial Associates on Caribbean Coral Reefs by Kathleen Michelle Morrow A dissertation submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Auburn, Alabama December 12, 2011 Keywords: Coral reef, microbiology, macroalgae, competition, allelopathy, community ecology Copyright 2011 by Kathleen Michelle Morrow Approved by Nanette E. Chadwick, Chair, Associate Professor of Biological Sciences Mark R. Liles, Associate Professor of Biological Sciences Anthony G. Moss, Associate Professor of Biological Sciences Valerie J. Paul, Director of the Smithsonian Marine Station at Fort Pierce, FL Alan Wilson, Assistant Professor of Fisheries and Allied Aquacultures Abstract Scleractinian corals harbor eukaryotic and prokaryotic organisms that form dynamic mutualistic, parasitic and commensal associations with the coral host and exhibit substantial genetic and ecological diversity. The microorganisms that inhabit the surface mucosal layer, tissues, and calcium carbonate skeleton of corals may provide the first line of defense against microbial infection, and evidence suggests that they play an intrinsic role in host fitness and disease susceptibility. Protection may be provided through the production of potent antibiotics or by filling an otherwise available niche open to infection by opportunistic pathogens. As corals are increasingly affected by catastrophic epizootics and bleaching events, it becomes increasingly important to understand the composition of coral-microbial assemblages and what causes the shift from a healthy to a diseased state. Often we correlate disease stressors such as high water temperature, sedimentation, nutrient loading, and overfishing, all of which may inhibit a corals innate ability to mediate an optimal microbial assemblage. However, as corals succumb to an early death there is an increase in colonizable substratum, which has provided an ideal environment for the proliferation of macroalgae, sponges, and other competitive dominants under present-day conditions. Coral-associated microbiota may be severely affected by the physical encroachment and allelochemicals exuded by encroaching organisms. This dissertation examines what is generally known about coral-microbial associations, briefly touching on coral disease and coral-algal interactions, followed by a laboratory assay that examines the allelochemical activity of common macroalgal extracts on coral reef microorganisms (Chapter 2). Additionally, I describe the species-specificity and geographic continuity of microbial assemblages associated with two common Caribbean coral species, Montastraea faveolata and Porites astreoides, in Belize, Florida, and St. Thomas (Chapter 3). Finally, I specifically examine the effect of encroaching macroalage and their allelochemicals on coral microbiota (Chapters 4 & 5). Better understanding of healthy coral-microbial associations and the ability of competing benthic organisms to physically or chemically shift these assemblages is critical to predicting reef resilience and the future of coral reef health. ii Acknowledgments We thank the Florida Keys National Marine Sanctuary for granting collection and research permits (FKNMS- 2008-019) and the Belize Fisheries Department for permits to collect coral mucus samples. The Harbor Branch Oceanographic Institute at Florida Atlantic University Center for Marine Biomedical and Bio- technology Research, Mote Marine Laboratory, University of the Virgin Islands MacLean Marine Science Center, and the Smithsonian Marine Station at Fort Pierce and the Smithsonian’s Carrie Bow Cay Field Station all provided invaluable logistical support. Dr. N. Fogarty, L. Huebner, N. Kirk, M. Newman, R. Ritson- Williams, J. Szczebak, and D. Weese provided field and laboratory assistance. My loving parents, Alan and Teresa Morrow, and boyfriend, Russell Carpenter, provided invaluable moral support. These studies are dedicated to my Poppop and Mommom, James and Theresa Malloy, for their constant love, encouragement, and support. This work was supported by a National Oceanic and Atmospheric Administration National Marine Sanctuary Program Nancy Foster Scholarship (KMM), NOAA’s ECOHAB program project NA05NOS4781194 (VJP), a Mote Marine Laboratory Protect our Reefs grant award POR 2007-30 (VJP), the Smithsonian Marine Science Network, and a Puerto Rico Sea Grant R-101-1-08 (NEC). iii Table of Contents Abstract ......................................................................................................................................... ii Acknowledgments ........................................................................................................................ iii List of Tables ................................................................................................................................ v List of Figures .............................................................................................................................. vi List of Abbreviations .................................................................................................................. vii Chapter 1: Review: Coral-Microbial Symbioses and Macroalgal Mediators ............................. 1 Introduction ..................................................................................................................... 1 Microbial Mutualisms ................................................................................................... 4 Macroalgal-Microbial Interactions ............................................................................... 12 Conclusion .................................................................................................................. 18 Chapter 2: Allelochemicals produced by Caribbean macroalgae and cyanobacteria have species-specific effects on reef coral microorganisms .................................................... 24 Introduction ................................................................................................................... 24 Methods .......................................................................................................................... 27 Results ........................................................................................................................... 31 Discussion ..................................................................................................................... 32 Chapter 3: Bacterial associates of two Caribbean coral species reveal species-specific distribution and geographic variability ......................................................................... 45 iv Introduction ................................................................................................................... 45 Methods .......................................................................................................................... 47 Results ........................................................................................................................... 53 Discussion ..................................................................................................................... 56 Conclusions ................................................................................................................... 63 Chapter 4: Coral-algal competition can mediate coral-associated microorganisms in situ ...... 74 Introduction ................................................................................................................... 74 Methods .......................................................................................................................... 77 Results ........................................................................................................................... 83 Discussion ..................................................................................................................... 86 Chapter 5: Allelochemicals produced by Caribbean macroalgae can alter coral-microbial assemblages in situ .......................................................................................................... 99 Introduction ................................................................................................................... 99 Methods ........................................................................................................................ 101 Results ......................................................................................................................... 107 Discussion ................................................................................................................... 110 References ............................................................................................................................... 124 v List of Tables Table 1.1: Coral Diseases ........................................................................................................... 19 Table 2.1: Bacterial bioassays ..................................................................................................... 38 Table 2.2: Bacterial taxa ............................................................................................................. 39 Table 2.3: 4-way ANOVA .......................................................................................................... 40 Table 2.4: Tukey post-hoc ........................................................................................................