SEASONAL AND SPATIAL FLUCTUATIONS OF THE PHYTOPLANKTON IN MONTEREY BAY A Thesis Presented to the Graduate Faculty of California State University, Hayward In Partial Fulfillment of the Requirements for the Degree Master of Arts in Biological Science by Russ Waidelich January, 1976 ABSTRACT The seasonal and spatial fluctuations of phyto­ plankton in Monterey Bay were described for an 18-month period. Low winter levels were mainly due to instabi­ lity of the water column, while the spring bloom was brought a·bout by the commencement of upwelling and the subsequent stabilization of the water column, with resi­ dence time of water regulating chlorophyll concentra­ tions. The summer minimum shortly followed the cessa­ tion of upwelling, when it appeared that nitrates were limiting, although zooplankton was a major factor in re­ ducing the algal standing stock at this time. Adequate illumination and relaxation of grazing pressure rather than specificity of water type appeared to be the major factors regulating the occurrence of the fall bloom, indicating that the seasonal pattern of Monterey Bay conforms generally to that of the mid­ latitude marine ecosystems. An examination of the spatial distribution o.f phytoplankton revealed lower values over the canyon during upwelling months due to advection of water to the shelf areas, and lower values in the same area during non-upwelling months due to subsidence or downwelling and tur·bul enc e . ii ACENOWLEDGlVJENTS Many people were responsible for helping to make this thesis possible. I would first like to thank my major advisors, Dr. Mary Silver and Dr. John Martin, for their valuable advice and support. In addition, the other memters of my committee, Dr. William Broenkow and Dr. James Nybakken, gave their time freely. I am indebted to the staff and students of Moss Landing Marine La-boratories for making this work possible. A special thanks goes to Jane Kinsley for her help and encouragement during the final stages of this work. iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS iv LIST OF FIGURES vii INTRODUCTION . 1 MONTEREY BAY AS AN ENVIRONIVIENT 8 PHYSIOGRAPHY 8 CLIMATE 12 CALIFORNIA CURRENT SYSTEM 17 SEASONAL OCEANOGRAPHIC CHANGES IN MONTEREY BAY . 18 CIRCULATION OF MONTEREY BAY 19 METHODS 21 STATIONS SAMPLED 21 BIOLOGICAL AND PHYSICAL DATA 23 STATISTICAL TREATMENT OF DATA 26 RESULTS 27 SEASONAL PHYTOPLANKTON CYCLES OF MONTEREY BAY . 39 STATISTICAL DIFFERENCES OF THE SEASONAL PHYTOPLANKTON CYCLES 52 SEASONAL NITRATE CYCLES FOR MONTEREY BAY 53 DISCUSSION . 58 SEASONAL VARIATIONS OF PHYTOPLANKTON STANDING STOCK . 58 v vi Page FALL BLOOM OF 1971 . ' • t • • • • ' • • • • .. 90 THE TIMING OF THE SPRING PHYTOPLANKTON MAXIMUM 98 FACTORS CONTROLLING THE OCCURRENCE AND COMPOSITION OF THE FALL BLOOM 101 PHYTOPLANKTON-ZOOPLANKTON RELATIONSHIPS 104 SPATIAL DISTRIBUTION OF PHYTOPLANKTON IN MONTEREY BAY . 111 FACTORS INFLUENCING LOCATION OF UPWELLING 113 SUMMARY 116 LITERATURE CITED . 120 LIST OF FIGURES Figure Page 1. Hydrografic sampling stations in Monterey Bay, California. 4 2. Numbers 1 through 6: Calcofi hydro­ grafic sampling stations, 1954-1960. Arrows represent surface movement in Broenkow's drogue study, 1972. 6 J. Monterey Bay, California. 9 4. Location of sewage outfal1s in Monterey Bay. 11 5. Seasonal light curve for Monterey Bay. · · · · · · · · · · 16 6. Vertical distribution of temperature ( °C) in Monterey Submarine Canyon (Stations 1115 and 1157). 29 7· Distribution of surface temperature (°C) of Monterey Bay, April 197J. JO 8. Distribution of surface temperature (°C) of Monterey Bay, June 1972. Jl 9. Distribution of surface temperature (°C) of Monterey Bay, July 1972. J2 10. Distribution of surface temperature (°C) of Monterey Bay, August 1972 .. JJ 11. Distribution of surface temperature (°C) of Monterey Bay, October 1972. J4 12. Distribution of surface temperature (°C) of Monterey Bay, November 1972. J5 1J. Distribution of surface temperature (°C) of Monterey Bay, January 197J. J6 vii viii Figure Page 14. Stability diagram for station 1115 in Monterey Bay for 1972. Individual figures combine a depth versus temperature profile and its mirrored image. .38 15. Monthly variation of average chlorophyll a (mg/m2) in upper 10 m water in Monterey Bay. 41 16. Division of Monterey Bay into regions for the purpose of comparing monthly variation of parameters. 42 17. Alternative division of Monterey Bay into regions for the purpose of comparing monthly variation of parameters. 18. Monthly varia~ion of average chloro­ phyll a (mg/m ) in upper 10 m water of inshore and offshore regions of Monterey Bay. 46 19. Monthly variation of nitrate concen­ tration (ug-at/liter) in surface water of inshore and offshore regions of Monterey Bay. 48 20. Monthly varia~ion of average chloro­ phyll a (mg/m ) in upper 10 m water for north, south, and central regions of Monterey Bay. 50 21. Monthly variation of nitrate concen­ tration (ug-at/liter) in surface water for north, south, and central regions of Monterey Bay. 57 22. Distribution of surface salinity of Monterey Bay, February 197.3. 60 2J. Distribution of nitrate concentration (ug-at/liter) in surface water of Monterey Bay, March 1972. ix Figure Page 24. Distribution of surface temperature (OC) of Monterey Bay, March 1972. 65 25. Distribution of average chlorophyll a (mg/m2) in upper 19 m water in - Monterey Bay, March 1972. ..... 66 26. Distribution of average chlorophyll a (mg/m2) in Monterey Bay, April 1972.-. 67 27. Distribution of surface temperature (oc) of Monterey Bay, April 1972. 28. Northwest wind stress for Monterey Bay, October 1971 to April l97J. 71 29. Distribution of average chlorophyll a (mg/m2) in upper 10 m water in - Monterey Bay, May 1972. ..... 7J JO. Distribution of surface temperature (°C) of Monterey Bay, May 1972. 74 Jl. Distribution of nitrate concentration (vg-at/liter) in surface water of Monterey Bay, May 1972. ..... 75 J2. Distribution of apparent bxygen utilization (vg-at/liter) in surface water of Monterey Bay, May 1972. 76 JJ. Distribution of average chlorophyll a (mg/m2) in Monterey Bay, June 1972. 78 J4. Distribution of surface salinity in Monterey Bay, June 1972. ..... 79 J5. Distribution of nitrate concentration (vg-at/liter) in surface water of Monterey Bay, June 1972. 80 J6. Distribution of nitrate concentration (ug-at/liter) in surface water of Monterey Bay, July 1972. ..... 82 X Figure Page .37· Monthly variation of average chlorophyll a (mg/m2) in upper 10 m water and zooplankton bio­ mass (ml/m3) in upper 15 m water of Monterey Bay. (Zooplankton volumes were not determined after August 1972.) ...... 85 J8. Distri·b~tion of average chlorophyll a (mg/m ) in upper 10 m water in Monterey Bay, September 1972. ... 87 .39· Distribution of surface temperature (°C) of Monterey Bay, September 1972. ............. 88 L!-0 • Distribution of nitrate concentration (ug-at/liter) in surface water of Monterey Bay, September 1972. ... 89 41. Distribution of average chlorophyll a (mgjm2) in upper 10 m water in Monterey Bay, October 1971. ... 92 42. Distribution of surface temperature (°C) of Monterey Bay, October 1971. 93 4J. Distribution of nitrate concentration (ug-at/liter) in surface water of· Monterey Bay, October 1971. .. 94 44. Distribution of apparent oxygen utilization (ug-at/liter) in surface water of Monterey Bay, October 1971. 95 45. Distribution of ammonia concentration (ug-at/liter) in surface water of Monterey Bay, October 1971. .... 96 INTRODUCTION The importance of phytoplankton as the founda­ tion of marine food chains has been long established (Haeckel 1890; Johnstone 1908; Lohmann 1911). Seasonal fluctuations of phytoplankton standing stock and the general relationship of these primary producers to other trophic levels, while sometimes complex, is also well established. Brandt (1902) was the first to propose that Liebig's law of the minimum, with respect to nutrients, be used to partially explain the seasonal differences in phytoplankton standing stocks. Nathansohn (1906) sted that vertical currents were involved in the circulation of phytoplankton nutrients. Since the turn of the century, a great number of investigations have been completed on seasonal phytoplankton cycles and the tors that regulate these systems. Most work has been done in the mid-latitudes, although extensive research s also been undertaken in both the tropical and polar ceions of the sea. Most early investigations of upwelling areas were primarily concerned with the physical and chemical pects of the systems. Moberg (1928) was one of the irst to relate increases in the diatom standing stock 1 2 to the chemical environment of upwelled water. In the last decade there has been a tremendous increase in the studies of the upwelling phenomena and its subsequent biological ramifications (Forsberg 1963; Curl and Small 1965; Smayda 1966; and others). This increased interest may be related to the quest for more food from the sea to support the ever-increasing hu'man population. Ryther (1969) has estimated that about 50% of the world's fish supply is produced from upwelling areas. Monterey Bay is a known region of upwelling. The bay was one of the major sardine fishing grounds on the west coast of the United States until this fish population declined in the early l950's (Wolf 1958), yet only a few major plankton-related studies have been completed in the bay. Bigalow and Leslie (1930) concluded that upwelling was the major source of nutrients for near surface waters here. Bolin and Abbott (1963) recorded bi-weekly changes ln phytoplankton abundance and composi­ tion from 1954 to 1960 and established an average annual cycle. This cycle revealed the yearly minimum during the months of November, December and January and the maximum in June. Following the spring maximum, the population constantly declined to the winter minimum, and no fall bloom was recorded. The investigation was incomplete ln that no nutrient data were collected. The conclusion that 3 nitrate was a limiting factor was inferred rather than proven, although it was probably correct.