UNIVERSITY OF HAWAII LIBRARY SPACIAL VARIABILITY IN PLANKTON SIZE STRUCTURE AND COMMUNITY COMPOSITION ALONG BIOGEOCHEMICAL GRADIENTS IN THE PACIFIC OCEAN A TIIESIS SUBMIITED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI'! IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN OCEANOGRAPHY AUGUST 2007 By Tara M. Clemente Thesis Committee: David M. Karl, Chairperson Matthew J. Church Karin M. Bjorkman We certify that we have read this thesis and that, in our opinion, it is satisfactory in scope and quality as a thesis for the degree of Master of Science in Oceanography. ACKNOWLEDGEMENTS I would like to thank my committee members for their time, encouragement, support and advice. My primary advisor, Dave Karl, who has challenged me to think critically and guided me throughout this study; Matt Church, for always leaving his door open and for giving me insight throughout this project; and Karin BjOrkman, who has been instrumental throughout this entire project especially in both the field and lab. I would like to thank the members of the HOT team for all their support and for their friendships. I'd like to thank the officers and crew of the RfV Kilo Moana for providing a safe and comfortable work place. Thanks to all the BEACH-BASH participants for their hard work and assistance with sample collection and data analysis, in particular Chief Scientist Karin BjOrkman, Eric Grabowski and Dan Sadler. For help in analysis I wish to acknowledge Bob Bidigare and Stephanie Christensen for HPLC, Karin BjOrkman, Susan Curless and Claire Mahaffey for dissolved nutrients and Karen Selph for flow cytometry. I'd like to thank my friends who stood by me throughout these last couple of years and gave me countless hours of advice, support and ice cream. I'd especially like to thank my family, my mom and dad for always supporting my goals no matter how strange they may have been at times; and for my sisters Jamie and Tracey, who were always available for those late night phone calls. I wish to give a special thanks to David Nichols whose support, friendship, and ability to make me laugh throughout these many years has been incredible. Lastly, I acknowledge the National Science Foundation, the Gordon and Betty Moore Foundation, and the Hawaii Ocean Time-series for providing financial support. iii ABSTRACT The size structure of upper ocean plankton assemblages appears to play an important role in determining the efficiency of the biological carbon pump and the resulting magnitude of biologically-mediated carbon export to the deep sea. To evaluate spatial variability in the size structure and community composition of plankton assemblages in the upper ocean measurements of size-fractionated chlorophyll a (Chi a), phycoerythrin and adenosine 5' -triphosphate (A1P) concentrations along with picoplankton abundances and taxonomic pigment biomarkers were assessed during the BEACH-BASH transect cruise from American Samoa to Honolulu, Hawaii in March 2005. Sampling for this study spanned four different biogeochemical provinces including the oligotrophic South Pacific Subtropical Gyre (SPSG), the relatively nutrient-enriched equatorial upwelling provinces, the Pacific Equatorial Divergence (PEQD) and the North Pacific Equatorial Countercurrent (PNEC), and the oligotrophic North Pacific Tropical Gyre (NPTG). Overall, nutrient concentrations were highest in the PEQD province, coinciding with the strong westerly South Equatorial Current (SEC) and the region of equatorial upwelling, and lowest in the SPSG and NPTG. Chi a and phycoerythrin concentrations throughout the transect were overwhelmingly dominated by picoplankton (0.2-2 f.UD.), accounting for 45 - 60 % of the total Chi a and 80 - 95 % of the total phycoerythrin throughout the transect. Flow cytometry measurements indicate that the picoplankton community composition was dominated by cyanobacteria of two genera; Prochlorococcus spp. and Synechococcus spp. and these groups accounted for most of the Chi a biomass throughout the transect. Picoeukaryotes also contributed to picoplankton abundances; however iv despite the likelihood of many species being present they remain largely unidentified. Total microbial biomass estimates via particulate ATP (P-ATP) measurements showed high variability with the occasional occurrence of larger heterotrophic organisms (>20 J.Lffi and 2-10 J.Lffi) which are not accounted for in Chi a biomass estimates. However, their distribution is sure to play an important role in regulating size structure and food web dynamics. Measurements of taxonomic pigment markers by HPLC confirmed the overwhelming dominance of prochlorophytes and cyanobacteria throughout the transect, however a transition in community composition in the PEQD province was observed. This transition was attributed to the increase in taxonomic pigment markers of chromophyte microalgae (i.e. prymnesiophytes, pelagophytes and diatoms). v TABLE OF CONTENTS Section Acknowledgements ..................................................................................ii Abstract ...............................................................................................iv List of Tables .......................................................................................viii List of Figures ........................................................................................ix Chapter I. Introduction ............................................................................. 1 Chapter 2. Spatial variability in plankton size structure and community composition along biogeochemical gradients in the Pacific Ocean ...........•......................5 2.1 Introduction .............................................................................5 2.1.1 Plankton size structure and community composition ................... 5 2.1.2 Biogeochemical provinces .................................................8 2.1.3 Equatorial Pacific Ocean ................................................. 11 2.1.4 Size-fractionation ..........................................................16 2.1.5 Objectives of this study .................................................. .17 2.2 Methods ............................................................................... 18 2.2.1 BEACH-BASH data ...................................................... 18 2.2.2 Sample collection and analysis ...........................................18 2.2.2.1 Nutrient analysis ................................................18 2.2.2.2 Chlorophyll a ................................................... 21 2.2.2.3 Phycoerythrin ...........•....................................... 22 2.2.2.4 Adenosine 5'-triphosphate (ATP) ........................... 23 2.2.2.5 Flow cytometry ................................................ 24 vi 2.2.2.6 HPLC pigments ................................................ 25 2.3 Results ................................................................................. 28 2.3.1 Habitat characteristics ....................................................28 2.3.1.1 Biogeochemical provinces ....................................28 2.3.1.2 Latitudinal distribution of temperature, salinity and Chl a .........................................................31 2.3.2 Nutrient distributions .....................................................33 2.3.2.1 Latitudinal distribution of dissolved inorganic nutrients.. 33 2.3.2.2 Dissolved inorganic nutrient ratios .................•........35 2.3.3 Plankton size structure ••••••••••••••••••.•.•••••••••••••••••••••.•.•.••.• 37 2.3.3.1 Chlorophyll a ...................................................37 2.3.3.2 Phycoerythrin ...•............................................•..42 2.3.3.3 Adenosine 5'-triphosphate (ATP) ........................... 44 2.3.4 Picoplankton community structure and taxonomic distribution ......47 2.3.4.1 Flow cytometry .............................•................. .47 2.3.4.2 HPLC pigments ................................................ 51 2.4 Discussion .............................................................................59 2.4.1 Nutrient dynamics .........................................................59 2.4.2 Phytoplankton size structure .............................................62 2.4.3 Community structure and taxonomic composition ...................67 2.4.4 Implications for the biological pump .......................•...........75 Chapter 3. Conclusions ...........................................................................77 References ...........................................................................................79 vii LIST OF TABLES 1. Detection limits, precision estimates and observed ranges .•..............................20 2. Abbreviations and taxonomic affinities of photosynthetic pigments .........•..........26 viii LIST OF FIGURES Figures 1. Conceptual view of major controls on recycled vs. export production .................• 6 2. Classification of planktonic organisms based on size ......................................7 3. BEACH-BASH transect cruise track ..........................................................9 4. Biogeochemical provinces sampled during BEACH-BASH .............................10 5. ADCP data showing current velocities ..................................................... 12 6. Sea surface temperature, wind and anomalies from TAD arrays ........................ 15 7. Depth profiles of temperature, chlorophyll a and soluble reactive phosphorus in each of the biogeochemical provinces ..................................................