FISH-INDUCED SEDIMENT RESUSPENSION - EFFECTS ON PHYTOPLANKTON BIOMASS AND COMMUNITY STRUCTURE IN A SHALLOW HYPEREUTROPHIC LAKE

An in situ mesocosm experiment was performed at Old Woman Creek Estuary, OH, to assess the importance of fish-induced sediment resuspension in regulating phytoplankton biomass and community structure. Six polyethylene tubes (1 m diameter x 2 m long) were placed into the lake, enclosing portions of the water column and sediments. Three duplicated treatments were established: (i) control, no fish; (ii) fish, stocked with small fish from the lake; and (iii) fish/net, stocked with fish, but into tubes with coarse nets suspended above the sediments to prevent resuspension. Total P concentrations and algal biomass in the fish tubes became markedly higher than the fish/net and control tubes. Centric diatoms and small cryptomonads were the initial dominants. In the lake and fish tubes, this community was replaced by nanochlorophytes. In the fish/net and control tubes, a very different succession occurred, where large cryptomonads became dominant. These results indicate that sediment nutrient resuspensions by fish activities can maintain a phytoplankton community in an immature state, with small r-selected dominants. When sediment nutrient resuspension was prevented (in the fish/net and control tubes), larger algal species increased in relative biovolume, regardless of whether fish were present.