PARENT SESSION
Oral Session #39: Invasions: Effects of invaders -- Aquatic, marsh, riparian. Presiding: C. Kolar.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Madison Ballroom C.
Mussels and Microcystis: Do zebra mussels promote blue-green algal blooms in oligotrophic lakes?
Wilson, Alan1, Raikow, David2, Sarnelle, Orlando1, Hamilton, Stephen2, 1 2
ABSTRACT- Anecdotal evidence suggests that the invasive bivalve, Dreissena polymorpha, may promote blue-green algal blooms in recently invaded North American lakes. For example, massive blooms of Microcystis aeruginosa were observed in Lake Erie and Saginaw Bay, Lake Huron, after zebra mussel establishment. However, direct experimental evidence of the effects of zebra mussels on blue-green biomass in nature is largely lacking. To examine the influence of zebra mussel density on phytoplankton abundance and species composition, we conducted a large-scale limnocorral experiment in an oligotrophic lake that has experienced Microcystis blooms since Dreissena establishment. Twelve large polyethylene enclosures (2.5m wide x 10m deep; volume = 40,000L) were stocked with zebra mussels at biomass densities ranging from 0 - 10 g dry tissue mass/m2 (11 treatments) and followed for four weeks. These densities bracketed our estimates of the average Dreissena density in the lake. For treatments at or below the lake-wide Dreissena average, zebra musssels had a negative effect on the biomass of both blue-greens and total phytoplankton. For treatments above the lake-wide average, the Dreissena effect was reversed, with both blue-green and total phytoplankton biomass increasing with Dreissena density. We attribute the latter effect to enhanced nutrient availability stemming from high mussel mortality in treatments above the lake-wide average. Thus, our results suggest that, for densities of zebra mussels that are at or below carrying capacity, Dreissena grazing does not promote blue-green blooms, in contrast to what has been suggested for the Great Lakes.
KEY WORDS: Dreissena polymorpha, Microcystis aeruginosa