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Thesis Abstract – Burr (1991)


Fluctuations in the Zooplankton Community of pHake Lake Over a Three Month Period

Author and college:

Susan Burr, Pomona College


May 3, 1991


Bachelor of Arts in Biology


Larry Oglesby, Pomona College


This study examines seasonal fluctuations of the zooplankton community in pHake Lake, a small, artificial lake in Claremont, California. Physical parameters such as temperature, oxygen, and light intensity were measured in the fall of 1990 from September to November and in 1991 from February to April. Zooplankters were sampled bimonthly from February to April in vertical net hauls and surface tows. Total numbers of organisms in 5 mL subsamples and percent of total of young Daphnia, Daphnia pulex, D. rosea, D. laevis, Bosmina longirostris, and Orthocyclops modestus were determined and compared between surface and bottom tows and between sampling dates. The physical parameters of the lake did not vary greatly over the sampling period, though a thermocline was present in the euphotic zone varied throughout the year. Definite correlations were not found between the zooplankton community and physical characteristics of the lake, but community was seen to change in composition and size throughout the three month study. Density was greater in the bottom to surface than in the surface tows throughout the year, though relative abundance of different species was similar between the two tows. A shift in competitive advantage was seen in March when D. pulex became more abundant and D. rosea decreased in abundance. B. longirostris and D. laevis were present in significant numbers on only one sampling date each. Biological factors, as opposed to changes in the physical parameters, are most likely responsible for these changes in populations, though they were untestable in this experimental design.

For more information:

Contact Gail Sundberg – gail.sundberg@pomona.edu

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