Document: JEF-3-74-4

Long-term effects of a short-term lake food web manipulation: Tuesday Lake 12 years later.

HOUSER, J.N.* ¹, C.E.H.SCHEELE ¹, T.E.ESSINGTON ², S.R.CARPENTER ¹ and J.F.KITCHELL ¹

University of Wisconsin, Madison, WI 53706 USA ¹
National Marine Fisheries Service, Honolulu, HI USA ²

Abstract:
A temporary, whole-lake food web manipulation that was within the scale of natural events (e.g. a fish winterkill) had effects lasting at least 12 years. In 1985, Tuesday Lake was subject to a strong food web manipulation: 90% of the planktivorous minnow population was removed, and piscivorous adult largemouth were added to the lake. The lower levels of the food web rapidly responded to the this switch from planktivore to piscivore dominance. Zooplankton mean size increased from 0.47 to 0.68 mm, Chaoborus biomass increased from 2.5 to 4.5 g/m², and chlorophyll a decreased from 11.6 to 5.4 ug/L. Significantly, the abundance of the dominant dinoflagellate, Peridinium limbatum, was greatly reduced during the manipulation, and it eventually disappeared from the lake. By the spring of 1987, the food web was restored to its premanipulation configuration. All largemouth bass were removed and the lake was restocked with minnows. Since the restoration of planktivore dominance in the lake in 1987, minnow biomass has risen to 49 kg/ha, substantially higher than the premanipulation minnow biomass of 24 kg/ha. The high biomass of minnows maintains a zooplankton biomass lower than premanipulation levels. However, chlorophyll a still remains low (4.1 ug/L), and Peridinium limbatum has not returned. Thus, 12 years after the restoration of a manipulated component of an ecosystem, the system remains in a state that is different from both premanipulation conditions and conditions during the manipulation suggesting that the recovery of ecosystems, even from brief manipulations, is a complex process.

Keywords: Food webs, fish, zooplankton, primary production

This abstract is being presented at: 10:30 AM in session:
Oral Session #54: Lake Ecology.