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Population Dynamics and Cohort Persistence of Acartia Californiensis (Copepoda: Calanoida) in Yaquina Bay, Oreccn

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Population Dynamics and Cohort Persistence of Acartia Californiensis (Copepoda: Calanoida) in Yaquina Bay, Oreccn AN ABSTRACT OF THE THESIS OF JOHN KENNETH JOHNSON for the degree of DOCTOR OF PHILOSOPHY (Name) (Degree) in OCEANOGRAPHY presented on 23 MAY 1980 (Major) (Date) Title: POPULATION DYNAMICS AND COHORT PERSISTENCE OF ACARTIA CALIFORNIENSIS (COPEPODA: CALANOIDA) IN YAQUINA BAY, ORECCN bstract Approved: Redacted for privacy The population dynamics of Acartia californiensis in Yaquina Bay, Oregon was studied by an integrated field and laboratory approach in 1972, 1973 and 1974. The planktonic phase (June - November) was characterized by well defined, persistent cohorts through time. Cohort.s were recognizable as distinct pulses in abundance at each copepodite stage and the adult stage. Generaticr. lengths typically ranged between 14-20 days. Several hypotheses to account for the unexpected persistence of cohorts were tested. These hypotheses included: a) periodic food limitation; b) tidal flushing; c) interspecific competition with Acartia claus!; and d) intense, size-selective predation on adult stages by planktivorous fishes. Measurements of chlorophyll 1evis (i.e. phytopiankton standing stocks) and primary productivity rates provided indirect evidence that food levels are seldom limiting for either development and growth or fecundity of A. californiensis. Chlorophyll levels remained high and relatively stable (ca 5-6 mg with. little evidence of grazing pressure during the summer population explosion of A. californiensis. No clear correlation was demonstrated between low level fluctuations of chlorophyll and tidal periodicity. Food quality remained high based on the measure of production per unit chlorophyll (assimilation ratios 6). Comparison of predicted and observed field development rates of A. californiensis provided a second and more direct test of the adequacy of food supplies. Field development rates, estimated from midpoints of area under the curve for successive copepodite stages, were linear within a cohort (least squares regression,r2O.95), implying isochronal development between stages. Predicted development (Blehrâdek temperature function) was either slightly longer than or equal to observed development times, demonstrating that field develop- ment was essentially temperature dependent and likely not food limited. Tidal flushing removed a maximum of 3.4-8.7% of the population per day based on a numerical flow model which assumed passive behavior. However, utilization of the landward flowing countercurrent and residence in the null zone of the estuary (area of longest advection time) probably minimized tidal flushing losses. Competition with A. clausi was concluded to be insignificant because of differences in position in the estuary of population centers, physiology, and probably grazing behavior in an apparently non-limiting food environment. However, A. clausi probably captures a significant fraction of A. californiensis nauplii daily. Naupliar mortality substantially increased with time of season. This seasonal decline possibly resulted from increasing predation from A. clausi although no data are available. In contrast, copepodite mortality was highest in the early and late season, but very low during the mid-season. This pattern is attributed to low survival during marginal physical conditions for growth and low predation during favorable physical conditions. Abundance cycles of adults were primarily controlled by intense, size-selective predation by visual plariktivores. Predators included Engraulis mordax (northern anchovy), Atherinops affinis (top smelt), ypomesus pretiosus (surf smelt) , Alosa sapidissirna (American shad), and Ciupea ns (Pacific herring). Gut contents revealed a feeding electivity for adult females, neutral electivity for the smaller males, and selection against copepodites. Cohort persistence was concluded to result primarily from the short life expectancy of adult females (3-6 days), with minor reinforcement from spring tides. The winter and spring months are passed as resting eggs in the sediments. Experimental results indicated that dormancy in A. califor- niensis eggs is induced by temperatures below 15°C in two ways 1) cold-adapted females spawn true resting eggs, which exhibit major differences in hatching and survival rates from non-dormant eggs under similar conditions; 2) non-dormant eggs spawned above15°C may become dormant and have short-term viability at temperatures below15°C. Salinity does not induce dormancy. Hatching results of field-collected resting eggs at naturally occurring temperature-salinity combinations demonstrate that termina- tion of dormancy is also primarily temperature dependent. Salinity, however, regulates rate and success of hatching. In addition, heavy naupliar mortality occurs following hatching at low salinities. Substantial hatching may occur in the field over much of the year. Since subsequent survival and population growth depend on the presence of favorable temperature and salinity conditions, nauplii which hatch during the salinity winter and spring months in Yaquina Bay must be lost. This phenomenon is viwed as a "leaky' population diapause. Population Dynamics and Cohort Persistence of Acartia californiensis (Copepoda: Calanoida) in Yaquina Bay, Oregon by John Kenneth Johnson A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed Nay 23, 1980 Commencement June, 1981 APPROVED: Redacted for privacy Associate Professor of Oceanography in charge of major Redacted for privacy Dean of Oceanography Redacted for privacy Dean of Graduate School Date thesis is presented 23 May 1980 Typed by Kathleen Johnson for John Kenneth Johnson ACKNOWLEDGEMENTS I am deeply indebted to many individuals who have contributed much in numerous and varied ways to the successful completion of this doctoral dissertation. Foremost among the professionally trained is my academic advisor and friend, Dr. Charles B. Miller.Charlie has willingly and tirelessly provided invaluable support, guidance, and constructive suggestions at all phases of the research. In addition, Charlie has been an outstanding editor in reviewing my writing and logic. It has been a priviledge to have been his student. I am also very appreciative of the help and encouragement provided at sundry times by my committee members, DrS. Lawrence F. Small, Charles E. Warren, and Peter Dawson. This work has benefited from each of them. Special appreciation is also acknowledged for the positive inter- actions that I had over the years with fellow students. In particular, my off ice mates, William Peterson, Barbara Dexter, Julie Ambler, and Archie VanderHart, were of much help and taught me many things in daily work. Appreciation is also expressed for the help John Reed provided in developing a methodology to determine the volume of the Yaquina Bay estuary at various tide heights and by area. Dr. Michael Landry provided much help and information in my efforts to calculate mortality rates of adult and copepodite copepods. His methodology was largely adopted because of its effectiveness. P,braham Fleminger and Peter Sertic provided aid in resolving the taxonomic status of the Acartia populations from Los Penasquitos Lagoon, California, and upper Yaquina Bay.Joan Flynn helped in doing many of the salinity determinations. Steve Crane and Me Matson participated in many of the sampling trips and were always fun con- panions to have along. Many of the administrative staff members were also much help. Of special mention are Jeannie Rhodes and Miriam Ludwig, individuals who always seemed to have a smile and time to be personally interested in the success of others about them. Most of all, however, I wish to acknowledge my great debt to my special companion and wife, Kathy and my sonsJonathan, Aaron, David, Joel, and Joshua.Without their willing support at all times, and Kathy's help in typing all of the drafts, this work simply could not have been successfully finished to meet graduate school deadlines. Only they know the great personal sacrifices that the last six months of writing required of them and the quality of family life as I worked full-time for the Pacific Marine Fisheries Commission and worked on the dissertation at night and on weekends. Special appreciation is also acknowledged for my employer, Dr. John Harville, who supported my efforts to finish by allowing me to have flex working hours when necessary. This research was supported in part by the Oregon State t3niver- sity Sea Grant College Program under the Office of Sea Grant (NOAA), #04-6-158-44094. TABLE OF CONTENTS SECTIONI. INTRODUCTION 1 STATEMENT OF THE PROBLEM 3 SECTIONII. PHYSICAL CHARACTERISTICS OF YAQUINA BAY 7 A. LOCATION AND GENERAL DESCRIPTION 7 B. CLIMATIC CONDITIONS 7 C. TIDAL CONDITIONS 13 D. SALINITY STRUCTURE 15 E. WATER TEMPERATURES 15 F. COLLECTION OF PHYSICAL DATA 16 G. RESULTS AND DISCUSSION 16 SECTIONIII. PHYTOPLANKTON STANDING CROP AND PRODUCTIVITY 26 A. METHODS 26 1. CHLOROPHYLL PIGMENTS 26 2. PRIMARY PRODUCTION ESTIMATES 27 B. RESULTS 30 1. PHYTOPLANKTON COMMUNITY .30 2. CHLOROPHYLL a PATTERNS 30 3. INCIDENT SOLAR RADIATION 37 4. EUPHOTIC ZONE DEPTH 5. PRIMARY PRODUCTION STUDIES 39 SECTIONIV. ABUNDANCE AND DISTRIBUTION OF ACARTIA CALIFORNIENSIS 58 A. METHODS 58 B. RESULTS 61 1. FIELD DISTRIBUTION PATTERNS 61 2. FIELD POPULATION CYCLES: POPULATION CENTER MODEL 61 3. FIELD ABUNDANCE CYCLES: TOTAL ESTUARY MODEL 69 4. COHORTS AND TIME BOUNDARIES 73 5. COMPARISON OF ADULT ABUNDANCE CYCLES WITH CHLOROPHYLL, PHAEOPHYTIN AND TIDES 78 6. ADULT SEX RATIOS IN
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