Chlorophyll budgets: repsonse to food web manipulation

Budgets for chlorophyll a and selected degradation products were constructed during summer stratification in 1984 and 1985 in two lakes. In Paul Lake, the reference ecosystem, pigment sedimentation showed no significant interannua] differences. In Tuesday Lake. fish manipulations in May 1985 changed the zooplankton from an assemblage of Bosmina and small cyclopoids to one of large c!adoceran grazers. Sedimentation of pigments, especially the grazing indicator pheophorbide a, increased significantly as the grazer assemb­lage changed. Mean grazer size was positively related to pheophorbide deposition rate in both lakes. Results of this whole-lake experiment indicate that major changes in lake food webs alter pigment deposition rates.