Algal Dynamics and Tropohic Interactions in the Recent History of Frains Lake, Michigan

Abstract

Analysis of a 10—m sediment core taken from the center of Frains Lake, Michigan, reveals distinct changes in diatom and chrysophycean cyst assemblages following European settlement °1830 AD. The presettlement planktonic diatom flora was dominated by Cyclotella species. The postsettlement flora was dominated first by eurytopic taxa, including Melosira granulata, Fragilaria construens, and F. crotonesis, and then by a complex of small Stephanodiscus species, particularly S. hantzschii. Cluster analysis and principal component analysis indicate three major stages in the recent development of Frains Lake, the greatest shift in the diatom assemblage occurring with settlement. Diatom succession bears a striking resemblance to patterns in other North American and European lakes. Stockner's A/C (Araphidineae/Centrales) ratios does not adequately indicate recent changes in the trophic status of Frains Lake. The recent succession of diatoms does agree with predictions based on the Si:P ratio and resource—based theory. Kerfoot's hypothesis that an increase in planktivorous fish caused a shift in postsettlement zooplankton composition is evaluated on the basis of algal microfossil data. I propose that shifts in the algal assemblage and other resources have influenced zooplankton community structure.