AN ABSTRACT OF THE THESIS OF Mark A. Brzezinski for the degree of Doctor of Philosophy in Oceanography presented on January 8, 1987. Title: Physiological and Environmental Factors Affecting Diatom Species Competition in a Gulf Stream Warm-Core Ring Redacted for privacy Abstract Approved: - David M. Nelson The physiology of two diatom species, Thalassiosira rotula Meunier (clone 411) and Chaetoceros sp. cf. vixvisibilis Schiller (clone 847), isolated from Gulf Stream warm-core ring 82-B, was examined relative to their abilities to compete for limiting nutrients within the ring after spring stratification and depletion of nutrients from the surface layer. Specifically, the effects of pulsed nutrient supplies and differential cell sinking on competition for macronutrients were investigated. In addition, the silicon cycle within ring 82-B after seasonal stratification was examined to define the availability of silicic acid to the phytopl ankton. Silica production was substrate-limited and limitation appeared to increase during quiescent periods. Silica dissolution at times exceeded silica production in the surface waters, whereas net silica production was always measured within and below the nutricline, a pattern analogous to that of carbon production in two-layered photic systems. On average, over 80 % of the silica production occurring in the upper 80 m of the ring could be supported by in situ silica dissolution, i.e. "regenerated production". In contrast, 62 % of the silica production occurring in the upper 110 m prior to strat- ification was supported by "new" silicic acid. Chaetoceros sp. cf. vixvisibilis was the superior competitor with pulsed or continuous supplies of either nitrate or silicic acid in laboratory culture. In contrast, coexistence occurred with continuous or pulsed ammonium supplies, but only with a photocycle. Coexistence seemed to involve interactions between the photocycle and the timing or kinetics of nutrient uptake. Chaetoceros sp. cf. vixvisibilis had negligible sinking rates when growth-limited by silicic acid, nitrate or ammonium, while T. rotula had measurable sinking rates with all three nutrient limitations. Highest sinking rates (up to 0.66 m d-l) were observed with silicic acid limitation. The results of competition for either nitrate or silicic acid in cultures where fast sinking cells were removed preferentially revealed that differential cell sinking is not necessarily the major cause of species displacements in selective-loss cultures. The population dynamics of C. sp. cf. vixvisibilis, T. rotula and Leptocylindrus danicus within the ring were consistent with those predicted from their physiological attributes measured in culture. Physiological and Environmental Factors Affecting Diatom Species Competition in a Gulf Stream Warm-Core Ring by Mark A. Brzezinski A THESIS Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed January 8, 1987 Commencement June 1987 APPROVED: Redacted for privacy Professor of Oceanography in charge of major Redacted for privacy Dean of College 9/ Oceanography Redacted for privacy Dean of Graduate Date dissertation is presented January 8, 1987 Typed by M. A. Brzezinski for himself. Acknowledgements This thesis would never have been completed without the generous support, encouragement and advice of my major professor Dr. David Nelson. Dave always gave me enough rope to go off and make my own discoveries, but was always there when I was about to hang myself. his help and example greatly enriched my education and made me a better oceanographer. I would also like to thank the other members of my committee for their advice over the years and especially for their efforts in editing the various drafts of this dissertation. Tim Cowles and Bob Guillard generously provided equipment and logistical help during the several cruises I made from WHOl during my graduate research. Back at Oregon State, Julie Ahern spent untold hours preparing and analyzing samples for me. Sandy Moore, Steve Kokkinakis and Margaret O'Brien also helped with several experiments and various analyses. My thanks to them all. In addition, I'd like to thank Rick Gould, Greta Fryxell and Ted Smayda for allowing me to use some of their unpublished data. Thanks also to all my fellow graduate students for helping me persevere through the Insanity of graduate school. I'll never forget you folks. The National Science Foundation awarded Dave Nelson a grant, OCE-8017269, which foot the bill for much of my research and stipend. I'd like to acknowledge their support which allowed me to get on with the business of becoming a scientist rather than working at the local pizza joint to pay the rent. Table of Contents CHAPTER I General Introduction............................. 1 Nutrient and Phytoplankton Dynamics in the Sea ................................ 3 Criticaldepth ..... 3 New vs regenerated production ..... 5 Phytoplankton growth rates in the sea ............................... 8 Phytoplankton Nutrient Physiology: An Overview ............................ 9 Nutrient uptake ................... 9 Growth .......................... 11 Luxury uptake ..................... 14 Phytoplankton Competition .............. 17 Equilibrium approaches to phytoplankton competition ......... 17 Competition in a variable habitat 21 Differential Cell Sinking ............. 24 Choiceof Study Site ................... 25 Gulf Stream warm-core rings ....... 25 A brief history of ring 82-B ...... 26 Choice of Experimental Clones ........ 29 Summary of Objectives.......... 30 CHAPTER II Production and Dissolution of Biogenic Silica in the Surface Waters of a Gulf Stream Warm-Core Ring ............................................. 44 Abstract .................... .............. Introduction...................... ...... ... 46 Methods ..................................... 49 Results....... ............. ........... 58 Dissolved and particulate silica distributions ..................... 58 Concentration dependence of silica production ...... ....... 59 Silica production rates .......... 60 Silica dissolution rates .......... 60 Net production and net dissolution of particulate silica ............. 61 Discussion .................................. 62 Substrate limitation of biogenic silica production ............... .. 62 Silicon cycling within the upper 80 m .............................. 67 Silicon cycling within and below the nutrient-depleted surface layer 68 Character of the dissolving silica 69 Warm-core ring 82-B as a two-layer photicsystem .................... 71 Table of Contents - continued Comparison with silicon cycles in other systems..................73 Chapter III Interactions Between Periodic Nutrient Supplies and Photocycles Affect Phytoplankton Competition for Limiting Nutrients in Long-Term Culture.......102 Abstract.....................................102 Introduction.................................103 Methods......................................105 Results......................................111 Continuous light..................111 Ammonium competition experiments..................111 Ammonium uptake..............112 Light:dark cycle..................113 Ammonium competition experiments..................113 Ainmonium uptake...............114 internal ainxnonium pools......115 Competition for nitrate and silicic acid......................116 Discussion....................................117 Competitive displacement with ammoniuin limitation and continuous illumination......................118 Coexistence with ainmoniuni limitation and a photocycle.......119 Competition for nitrate and silicic acid......................125 Summary and Conclusions......................126 Chapter IV Differential Cell Sinking as a Factor Influencing Diatom Species Competition for Limiting Nutrients in Selective-Loss Culture.........................153 Abstract.....................................153 Introduction.................................154 Methods......................................156 Competition experiments......156 Sinking rate determinations.. 160 Displacement rates...........162 Daily growth rates...........162 Nutrient uptake rates........164 Results........................................165 Nitrate limitation................165 Silicic acid limitation 167 Direct sinking rate measurements 169 Growth rates......................170 Table of Contents continued Elemental composition ..............171 Yield of particulate silica and particulate nitrogen ...............173 Nutrient uptake ....................174 Nitrate .......................174 Silicic Acid ..................175 Observed vs predicted displacement rates .................175 Discussion ....................................176 Direct sinking rate measurements...176 Sinking rates calculated from cell budgets .......................178 Growth rates and competitive displacements ......................179 Apparent negative growth rates .....183 Summary ......................................186 Chapter V Diatom Species Succession in Gulf Stream Warm-Core Ring 82-B: Predictions Based on Experimental Results Versus Observed Species Dynamics ........... 213 Introduction ................................. 213 Methods ...................................... 214 Intercional variability ....... 215 Growth rate vs irradiance ..... 216 Growth rate vs silicic acid concentration ................. 216 Results and Discussion ........................ 217 Diatom species and habitat dynamics in warm-core