Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship 2013 Synechococcus distribution and abundance in the San Juan Archipelago, Salish Sea Katherine L. (Katherine Leigh) Brown Western Washington University Follow this and additional works at:https://cedar.wwu.edu/wwuet Part of theMarine Biology Commons Recommended Citation Brown, Katherine L. (Katherine Leigh), "Synechococcus distribution and abundance in the San Juan Archipelago, Salish Sea" (2013). WWU Graduate School Collection. 303. https://cedar.wwu.edu/wwuet/303 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. SYNECHOCOCCUS DISTRIBUTION AND ABUNDANCE IN THE SAN JUAN ARCHIPELAGO, SALISH SEA By Katherine Leigh Brown Accepted in Partial Completion Of the Requirements for the Degree Master of Science Kathleen L. Kitto, Dean of the Graduate School ADVISORY COMMITTEE Co-Chair, Dr. Suzanne Strom Co-Chair, Dr. Benjamin Miner Dr. Jude Apple MASTER’S THESIS In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the non- exclusive royalty-free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files. 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Katherine Leigh Brown October 9, 2013 SYNECHOCOCCUS DISTRIBUTION AND ABUNDANCE IN THE SAN JUAN ARCHIPELAGO, SALISH SEA A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment Of the Requirements for the Degree Master of Science By Katherine Leigh Brown August 2013 ABSTRACT Synechococcus, a unicellular cyanobacterium of about one micron in size, is one of the most prolific and abundant primary producers worldwide and, hence, has an important role in the phytoplankton community. This study sought to determine 1) the distribution and abundance of Synechococcus in the eastern San Juan Archipelago; 2) the environmental variables related most closely to abundance; and 3) the key grazers of Synechococcus in this ecosystem. Two stations were chosen, East Sound near Orcas Island, WA and Rosario Strait near Lopez Pass, for their differing hydrographic conditions. Sampling was conducted from June to September 2012. Water samples were taken at three depths at both stations twice a month June through August, and then approximately every three days for three weeks in September. A CTD (Conductivity, Temperature, and Depth) was lowered at each station to obtain environmental data from the water column. Water samples were used for nutrient analysis, size-fractionated chlorophyll a analysis, and for the enumeration of Synechococcus and the protist grazer community. Synechococcus abundance rose as high as 1.5 x 104 cells ml-1 at both East Sound and Rosario Strait in August. Synechococcus abundance and depth distribution were nearly the same at both stations despite the well-mixed environment at Rosario and the more frequently stratified environment at East Sound. Both stations were abundant in nitrate+nitrite and phosphate throughout the sampling period. However, chlorophyll a concentrations were unusually low July through August, a season that usually exhibits variable and episodically high concentrations. Of all the environmental variables analyzed, only salinity was correlated with Synechococcus abundance at both stations, and that correlation was negative. The importance of salinity as a predictor of abundance may be due to a physiological effect of fresher water that allows for increased biomass production, or simply to the dominant effect of salinity on water column stratification, which may provide a preferable growth environment for Synechococcus. Ciliates, heterotrophic nanoflagellates, and dinoflagellates were observed with ingested Synechococcus. Surprisingly, nanoflagellates were rarely observed with ingested cells. Dinoflagellates seemed to be the key grazers of Synechococcus in the eastern San Juan Archipelago, but there was no clear temporal pattern to the level of Synechococcus ingestion by any of the aforementioned grazers. iv ACKNOWLEDGEMENTS First and foremost, my warmest thanks go to my thesis advisor, Dr. Suzanne Strom, for her patience and support as well as the time she spent working with me to make this thesis the best it could be. Thanks to my co-advisor, Dr. Benjamin Miner, for his excellent ideas and open door. Another big thanks goes to my committee member, Dr. Jude Apple, for his constant encouragement and guidance through the maze of multivariate statistics. This work could not have been accomplished without the help of many people at Shannon Point Marine Center including the Strom lab: Kelley Bright and Kerri Fredrickson for teaching me all I know about epifluorescent microscopy, and Amelia Kolb for her assistance and companionship in the field, and for teaching me the lab techniques needed for this project. Thanks to Dr. Steve Sulkin and Gene McKeen for logistical and financial support for field work. Thank you to the captains of the R/V Zoea, Nate Schwarck and Jay Dimond, who gave their time and effort to providing a safe and successful field season. Thank you to Horng-Yuh Lee for her help conducting the nutrient analysis. This thesis was also supported financially by a grant from the National Science Foundation (1021189). v TABLE OF CONTENTS Abstract……………………………………………………………………………………...iv Acknowledgements…………………………………………………………………………..v List of Figures………………………………………………………………………………vii List of Tables……………………………………………………………………………….viii Introduction…………………………………………………………………………………..1 Materials and Methods…………………………………………………………………….....6 Results……………………………………………………………………………………….13 Discussion…………………………………………………………………………………...48 Salinity Correlation: A Physiological Effect of Salinity………………………….…49 Mixing at East Sound and Rosario…………………………………………………..53 The Nutrient Environment…………………………………………………………..55 Chlorophyll a and the Anomalous Decline of Light in 2012……………………….57 Synechococcus and a Diverse Microzooplankton Community……………………..60 Principal Components Analysis…………………………………………………….66 Conclusion…………………………………………………………………………..67 Literature…………………………………………………………………………………....69 Appendix A………………………………………………………………………………....74 Appendix B………………………………………………………………………………....75 Appendix C………………………………………………………………………………....76 Appendix D…………………………………………………………………………………77 vi LIST OF FIGURES Figure 1. Map of sampled stations in the San Juan Archipelago……………..........................7 Figure 2. Synechococcus abundance in East Sound and Rosario……………………………14 Figure 3. Average temperature at each station………………………………………………16 Figure 4. Average salinity at each station………………………………………....................18 Figure 5. Average density as sigma-t at each station………………………………………...20 Figure 6. Examples of chlorophyll a fluorescence depth profiles…………………………...22 Figure 7. Total daily PAR…………………………………………………………………....23 Figure 8. PAR anomaly data from 2002-2012……………………………………………….26 Figure 9. PAR anomaly data for years of past studies…………………………………….....27 Figure 10. Nitrate+nitrite concentrations at each station………………………………….....29 Figure 11. Phosphate concentrations at each station…………………………………….......30 Figure 12. Total chlorophyll a concentrations at each station…………………………….....32 Figure 13. Percentage of total chlorophyll a based on size-fractionated chlorophyll data.....34 Figure 14. Tidal range at each station………………………………………………………..36 Figure 15. Upwelling index……………………………………………………………….....37 Figure 16. Average Fraser River discharge………………………………………………….38 Figure 17. Average Fraser River discharge rate for years of past studies ……………….….40 Figure 18. Examples of grazers with ingested Synechococcus cells ………………………..43 Figure 19. Examples of grazer taxa………………………………………………………....44 Figure 20. Principal components analysis graphs for each station………………….............46 vii LIST OF TABLES Table 1. Correlation table for Synechococcus abundance and environmental variables…….17 Table 2. Percentage of surface light with depth at each station……………………………...24 Table 3. Abundance of protist grazer taxa at each station…………………………………...41 Table 4. Percentage of observed grazers feeding on Synechococcus at each station………..42 Table 5. Eigenvectors from Principal Components Analysis……………………………......47 Table 6. Summary of data from past studies in East Sound………………………………....59 viii INTRODUCTION The base of the ocean’s food web is composed of photosynthetic microorganisms called phytoplankton, which are essential to ocean ecosystems because they are the major primary producers (Pomeroy 1974). Life for a population of phytoplankton in the euphotic zone involves both gains and losses. In order for a phytoplankton bloom to occur, rates of gain must exceed rates of loss. Gain processes include cell division as well as water movement, or advection from an area rich in phytoplankton (Banse 1992). Because phytoplankton are microalgae, continued cell division can occur only when both light and nutrients are available for photosynthesis and biomass production. However, even if there was an uninhibited supply of light and nutrients, population growth could also be diminished by losses. These loss processes include sinking out of the euphotic zone, dilution by moving into an area of poor phytoplankton concentration, grazing by predators, and death by age, parasites, or viruses (Banse 1992). These processes must be taken into consideration when thinking about how a bloom occurs, and which variables might be affecting its successful initiation and eventual termination. The focus of this study is on growth related to light, nutrients, and movement of water masses, along with loss from grazing by protists. There is a food web of microbial producers and consumers called the microbial loop amid the ocean food web (Pomeroy 1992). In the microbial loop, dissolved organic matter (DOM) and inorganic nutrients released from phytoplankton by excretion, exudation, and diffusion is returned to the food chain through bacteria and grazing of bacteria by flagellates (3 to 10 µm) and microzooplankton (10 to 80 µm), including protist grazers such as ciliates (Azam et al. 1983). Production from the microbial community is either lost to trophic transfers or released as dissolved material such as ammonium, phosphate, and DOM within