PARENT SESSION
Oral Session #7: Aquatic Ecology: Stream ecosystems. Presiding: T. Ehlinger.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
Stream organism response to food web subsidies created by cyprinid spawning activity in a North temperate stream.
Willis, Theodore1, Magnuson, John1, 1
ABSTRACT- Like coastal streams and rivers, Midwestern streams of North America also experience seasonal migrations of spawning fishes. Cyprinids move from lakes where they over-winter into connected streams in late spring. Many prepare spawning nests and deposit eggs between late May and late July, creating a spatially and temporally heterogeneous arrangement of food and nutrients in the stream. In 2000 and early 2001 I investigated stream biota response to these seasonal food web subsidies in Allequash Creek, a second order stream located in Vilas County, WI. Piscivorous fishes showed a dramatic response to increases in cyprinid density. A number of largemouth bass (Micropterus salmoides) and northern pike (Esox lucius) from connected lakes became seasonal stream residents. Diet and movement analyses showed a preference for cyprinid prey and repeated use of the stream habitat compared to conspecifics in connected lakes. Species composition of large bodied macroinvertebrates collected from fish nests was different from that seen in similar non-nest substrates. Chlorophyll A tended to increase just downstream of areas with high nest density, and remained consistently high in these areas throughout the spawning season. Though less strong than responses seen in systems with anadromous marine fishes, Midwestern stream biota did respond to food web subsidies by spawning cyprinids.
KEY WORDS: subsidy, midwest stream, fish, food web