|Title||Changes in the benthic algal community and nutrient limitatin in Saginaw Bay, Lake Huron, during the invasion of the zebra mussel (Dreissena polymorpha)|
|Publication Type||Journal Article|
|Year of Publication||2002|
|Authors||Pillsbury RW, Lowe RL, Pan Y, Greenwood JL|
|Journal||Journal of the North American Benthological Society|
We conducted a series of nutrient manipulation experiments over the first 5 y of Dreissena colonization in Saginaw Bay, Lake Huron, to evaluate benthic algal nutrient limitation and community composition. We placed nutrient-diffusing substrata in the littoral zone of the Bay during 1991 (early Dreissena colonization) and from 1992 to 1995 (post-Dreissena colonization). The treatments consisted of P, N, and P+N additions, and a control. Chlorophyll a decreased through time from 1992 to 1995. Phosphorus limited biovolume only in 1994. Treatments with P additions had significantly more chlorophyll a than the controls each year after 1992. This result was consistent with an observed decrease in dissolved P throughout the study. Nitrogen additions had no significant effect throughout the 5 -y period. Major shifts in species composition did not result from nutrient additions but rather seemed to be consistent with changes in light penetration and Dreissena herbivory. Our data demonstrated that the pre-Dreissena benthic algal community was dominated by tychoplanktonic diatoms (i.e., Aulacoseira granulata and Tabellaria fenestrata), which would be susceptible to filter-feeding Dreissena. Early post-invasion conditions were marked by an increase in light penetration, and benthic algae were dominated by filamentous green algae (mostly Spirogyra sp.). Late post-invasion conditions were marked by a reduction of light caused by planktonic blooms of Microcystis sp., which were resistant to zebra mussel herbivory. The benthic algal dominance shifted to periphytic diatoms (i.e., Gomphonema clevei), which were also resistant to zebra mussel filter-feeding. A new equilibrium may be developing where Dreissena herbivory limits tychoplanktonic diatoms, which promotes Microcystis bloom, which in turn limits Dreissena filtering rates.