Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2005

Thesis Director

Charles Pederson

Thesis Committee Member

Robert Fischer

Thesis Committee Member

Scott Meiners

Abstract

Survival, and ultimately recruitment. of planktivorous juvenile fish is related to prey availability. Temperature regime and introduction of exotic species can change zooplankton community dynamics and alter trophic relationships between juvenile fish and their prey. Newton Lake, located in Jasper County, Illinois is used as a cooling reservoir for a coal burning power plant. Thermal effluent produced by the power plant is released into only one of two reservoir arms creating a temperature gradient. Newton Lake also contains Daphnia lumholtzi, an exotic zooplankter thought to create feeding difficulties for gape-limited predators like juvenile fish. It is within the context of temperature regime alteration and presence of an exotic species that I attempt to determine if zooplankton community dynamics in Newton Lake affect recruitment of juvenile largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus).

Limnetic zooplankton were sampled in Newton Lake from July 2003 - July 2004 to assess community structure as it relates to temperature regime. Bray-Curtis dissimilarity analysis and nonmetric multi-dimensional scaling indicate zooplankton community dynamics in Newton Lake were associated with temperature. Accordingly. zooplankton abundance and diversity was lowest during summer as a result of extremely high temperatures created by release of thermal effluent.

Littoral zooplankton communities and juvenile largemouth bass and bluegill were collected during 8 sample periods in the spring and summer of 2004 for determination of fish electivity in relation to prey availability. As with limnetic communities, littoral zooplankton structure was determined by temperature regime. Littoral communities also contained Daphnia lumholtzi, and based on gape length characteristics. bluegill may have difficulty ingesting this plankter resulting in an overall reduction in prey availability.

Juvenile fish exhibited specific zooplankton prey preferences related to gapelimitation and prey characteristics associated with motion and pigmentation. However. fish underwent dietary shifts as they matured with bass becoming more piscivorous while bluegill became more insectivorous. Both fish species displayed trophic adaptability in that they consumed the most profitable prey item (i.e. insects or other fish), but continued to supplement their diets with zooplankton. Therefore, this diet flexibility may allow juvenile fish in Newton Lake to avoid reduced survival and recruitment rates caused by low zooplankton prey availability and presence of Daphnia lumholtzi.

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